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<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">notebook_preamble</span> <span class="k">import</span> <span class="n">D</span><span class="p">,</span> <span class="n">DefinitionWrapper</span><span class="p">,</span> <span class="n">J</span><span class="p">,</span> <span class="n">V</span><span class="p">,</span> <span class="n">define</span>
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</pre></div>
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</div>
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<div class="section" id="recursive-combinators">
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<h1>Recursive Combinators<a class="headerlink" href="#recursive-combinators" title="Permalink to this headline">¶</a></h1>
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<p>This article describes the <code class="docutils literal notranslate"><span class="pre">genrec</span></code> combinator, how to use it, and
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several generic specializations.</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span> <span class="p">[</span><span class="k">if</span><span class="p">]</span> <span class="p">[</span><span class="n">then</span><span class="p">]</span> <span class="p">[</span><span class="n">rec1</span><span class="p">]</span> <span class="p">[</span><span class="n">rec2</span><span class="p">]</span> <span class="n">genrec</span>
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<span class="o">---------------------------------------------------------------------</span>
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||||
<span class="p">[</span><span class="k">if</span><span class="p">]</span> <span class="p">[</span><span class="n">then</span><span class="p">]</span> <span class="p">[</span><span class="n">rec1</span> <span class="p">[[</span><span class="k">if</span><span class="p">]</span> <span class="p">[</span><span class="n">then</span><span class="p">]</span> <span class="p">[</span><span class="n">rec1</span><span class="p">]</span> <span class="p">[</span><span class="n">rec2</span><span class="p">]</span> <span class="n">genrec</span><span class="p">]</span> <span class="n">rec2</span><span class="p">]</span> <span class="n">ifte</span>
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</pre></div>
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</div>
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<p>From “Recursion Theory and Joy” (j05cmp.html) by Manfred von Thun:</p>
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<blockquote>
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<div>“The genrec combinator takes four program parameters in addition to
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whatever data parameters it needs. Fourth from the top is an
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if-part, followed by a then-part. If the if-part yields true, then
|
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the then-part is executed and the combinator terminates. The other
|
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two parameters are the rec1-part and the rec2-part. If the if-part
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yields false, the rec1-part is executed. Following that the four
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program parameters and the combinator are again pushed onto the
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stack bundled up in a quoted form. Then the rec2-part is executed,
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where it will find the bundled form. Typically it will then execute
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the bundled form, either with i or with app2, or some other
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combinator.”</div></blockquote>
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<div class="section" id="designing-recursive-functions">
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<h2>Designing Recursive Functions<a class="headerlink" href="#designing-recursive-functions" title="Permalink to this headline">¶</a></h2>
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||||
<p>The way to design one of these is to fix your base case and test and
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||||
then treat <code class="docutils literal notranslate"><span class="pre">R1</span></code> and <code class="docutils literal notranslate"><span class="pre">R2</span></code> as an else-part “sandwiching” a quotation
|
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of the whole function.</p>
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||||
<p>For example, given a (general recursive) function <code class="docutils literal notranslate"><span class="pre">F</span></code>:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">F</span> <span class="o">==</span> <span class="p">[</span><span class="n">I</span><span class="p">]</span> <span class="p">[</span><span class="n">T</span><span class="p">]</span> <span class="p">[</span><span class="n">R1</span><span class="p">]</span> <span class="p">[</span><span class="n">R2</span><span class="p">]</span> <span class="n">genrec</span>
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||||
<span class="o">==</span> <span class="p">[</span><span class="n">I</span><span class="p">]</span> <span class="p">[</span><span class="n">T</span><span class="p">]</span> <span class="p">[</span><span class="n">R1</span> <span class="p">[</span><span class="n">F</span><span class="p">]</span> <span class="n">R2</span><span class="p">]</span> <span class="n">ifte</span>
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</pre></div>
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</div>
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<p>If the <code class="docutils literal notranslate"><span class="pre">[I]</span></code> predicate is false you must derive <code class="docutils literal notranslate"><span class="pre">R1</span></code> and <code class="docutils literal notranslate"><span class="pre">R2</span></code>
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from:</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="o">...</span> <span class="n">R1</span> <span class="p">[</span><span class="n">F</span><span class="p">]</span> <span class="n">R2</span>
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</pre></div>
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</div>
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<p>Set the stack arguments in front and figure out what <code class="docutils literal notranslate"><span class="pre">R1</span></code> and <code class="docutils literal notranslate"><span class="pre">R2</span></code>
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have to do to apply the quoted <code class="docutils literal notranslate"><span class="pre">[F]</span></code> in the proper way.</p>
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</div>
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<div class="section" id="primitive-recursive-functions">
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<h2>Primitive Recursive Functions<a class="headerlink" href="#primitive-recursive-functions" title="Permalink to this headline">¶</a></h2>
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<p>Primitive recursive functions are those where <code class="docutils literal notranslate"><span class="pre">R2</span> <span class="pre">==</span> <span class="pre">i</span></code>.</p>
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||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">P</span> <span class="o">==</span> <span class="p">[</span><span class="n">I</span><span class="p">]</span> <span class="p">[</span><span class="n">T</span><span class="p">]</span> <span class="p">[</span><span class="n">R</span><span class="p">]</span> <span class="n">primrec</span>
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||||
<span class="o">==</span> <span class="p">[</span><span class="n">I</span><span class="p">]</span> <span class="p">[</span><span class="n">T</span><span class="p">]</span> <span class="p">[</span><span class="n">R</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="n">i</span><span class="p">]</span> <span class="n">ifte</span>
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||||
<span class="o">==</span> <span class="p">[</span><span class="n">I</span><span class="p">]</span> <span class="p">[</span><span class="n">T</span><span class="p">]</span> <span class="p">[</span><span class="n">R</span> <span class="n">P</span><span class="p">]</span> <span class="n">ifte</span>
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</pre></div>
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</div>
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</div>
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<div class="section" id="hylomorphism">
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<h2><a class="reference external" href="https://en.wikipedia.org/wiki/Hylomorphism_%28computer_science%29">Hylomorphism</a><a class="headerlink" href="#hylomorphism" title="Permalink to this headline">¶</a></h2>
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<p>A
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<a class="reference external" href="https://en.wikipedia.org/wiki/Hylomorphism_%28computer_science%29">hylomorphism</a>
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is a recursive function <code class="docutils literal notranslate"><span class="pre">H</span> <span class="pre">::</span> <span class="pre">A</span> <span class="pre">-></span> <span class="pre">C</span></code> that converts a value of type
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<code class="docutils literal notranslate"><span class="pre">A</span></code> into a value of type <code class="docutils literal notranslate"><span class="pre">C</span></code> by means of:</p>
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||||
<ul class="simple">
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||||
<li>A generator <code class="docutils literal notranslate"><span class="pre">G</span> <span class="pre">::</span> <span class="pre">A</span> <span class="pre">-></span> <span class="pre">(B,</span> <span class="pre">A)</span></code></li>
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<li>A combiner <code class="docutils literal notranslate"><span class="pre">F</span> <span class="pre">::</span> <span class="pre">(B,</span> <span class="pre">C)</span> <span class="pre">-></span> <span class="pre">C</span></code></li>
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<li>A predicate <code class="docutils literal notranslate"><span class="pre">P</span> <span class="pre">::</span> <span class="pre">A</span> <span class="pre">-></span> <span class="pre">Bool</span></code> to detect the base case</li>
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<li>A base case value <code class="docutils literal notranslate"><span class="pre">c</span> <span class="pre">::</span> <span class="pre">C</span></code></li>
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<li>Recursive calls (zero or more); it has a “call stack in the form of a
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cons list”.</li>
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</ul>
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<p>It may be helpful to see this function implemented in imperative Python
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code.</p>
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<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">hylomorphism</span><span class="p">(</span><span class="n">c</span><span class="p">,</span> <span class="n">F</span><span class="p">,</span> <span class="n">P</span><span class="p">,</span> <span class="n">G</span><span class="p">):</span>
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<span class="sd">'''Return a hylomorphism function H.'''</span>
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<span class="k">def</span> <span class="nf">H</span><span class="p">(</span><span class="n">a</span><span class="p">):</span>
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<span class="k">if</span> <span class="n">P</span><span class="p">(</span><span class="n">a</span><span class="p">):</span>
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<span class="n">result</span> <span class="o">=</span> <span class="n">c</span>
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<span class="k">else</span><span class="p">:</span>
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<span class="n">b</span><span class="p">,</span> <span class="n">aa</span> <span class="o">=</span> <span class="n">G</span><span class="p">(</span><span class="n">a</span><span class="p">)</span>
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||||
<span class="n">result</span> <span class="o">=</span> <span class="n">F</span><span class="p">(</span><span class="n">b</span><span class="p">,</span> <span class="n">H</span><span class="p">(</span><span class="n">aa</span><span class="p">))</span> <span class="c1"># b is stored in the stack frame during recursive call to H().</span>
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<span class="k">return</span> <span class="n">result</span>
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||||
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<span class="k">return</span> <span class="n">H</span>
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</pre></div>
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</div>
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<p>Cf. <a class="reference external" href="http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.41.125">“Bananas, Lenses, & Barbed
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Wire”</a></p>
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<p>Note that during evaluation of <code class="docutils literal notranslate"><span class="pre">H()</span></code> the intermediate <code class="docutils literal notranslate"><span class="pre">b</span></code> values are
|
||||
stored in the Python call stack. This is what is meant by “call stack in
|
||||
the form of a cons list”.</p>
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</div>
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<div class="section" id="hylomorphism-in-joy">
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<h2>Hylomorphism in Joy<a class="headerlink" href="#hylomorphism-in-joy" title="Permalink to this headline">¶</a></h2>
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||||
<p>We can define a combinator <code class="docutils literal notranslate"><span class="pre">hylomorphism</span></code> that will make a
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hylomorphism combinator <code class="docutils literal notranslate"><span class="pre">H</span></code> from constituent parts.</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">H</span> <span class="o">==</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="n">c</span> <span class="p">[</span><span class="n">G</span><span class="p">]</span> <span class="p">[</span><span class="n">F</span><span class="p">]</span> <span class="n">hylomorphism</span>
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</pre></div>
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</div>
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<p>The function <code class="docutils literal notranslate"><span class="pre">H</span></code> is recursive, so we start with <code class="docutils literal notranslate"><span class="pre">ifte</span></code> and set the
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||||
else-part to some function <code class="docutils literal notranslate"><span class="pre">J</span></code> that will contain a quoted copy of
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||||
<code class="docutils literal notranslate"><span class="pre">H</span></code>. (The then-part just discards the leftover <code class="docutils literal notranslate"><span class="pre">a</span></code> and replaces it
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with the base case value <code class="docutils literal notranslate"><span class="pre">c</span></code>.)</p>
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||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">H</span> <span class="o">==</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="n">c</span><span class="p">]</span> <span class="p">[</span><span class="n">J</span><span class="p">]</span> <span class="n">ifte</span>
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||||
</pre></div>
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</div>
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<p>The else-part <code class="docutils literal notranslate"><span class="pre">J</span></code> gets just the argument <code class="docutils literal notranslate"><span class="pre">a</span></code> on the stack.</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">a</span> <span class="n">J</span>
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<span class="n">a</span> <span class="n">G</span> <span class="n">The</span> <span class="n">first</span> <span class="n">thing</span> <span class="n">to</span> <span class="n">do</span> <span class="ow">is</span> <span class="n">use</span> <span class="n">the</span> <span class="n">generator</span> <span class="n">G</span>
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<span class="n">aa</span> <span class="n">b</span> <span class="n">which</span> <span class="n">produces</span> <span class="n">b</span> <span class="ow">and</span> <span class="n">a</span> <span class="n">new</span> <span class="n">aa</span>
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||||
<span class="n">aa</span> <span class="n">b</span> <span class="p">[</span><span class="n">H</span><span class="p">]</span> <span class="n">dip</span> <span class="n">we</span> <span class="n">recur</span> <span class="k">with</span> <span class="n">H</span> <span class="n">on</span> <span class="n">the</span> <span class="n">new</span> <span class="n">aa</span>
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<span class="n">aa</span> <span class="n">H</span> <span class="n">b</span> <span class="n">F</span> <span class="ow">and</span> <span class="n">run</span> <span class="n">F</span> <span class="n">on</span> <span class="n">the</span> <span class="n">result</span><span class="o">.</span>
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</pre></div>
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</div>
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<p>This gives us a definition for <code class="docutils literal notranslate"><span class="pre">J</span></code>.</p>
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<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span> <span class="o">==</span> <span class="n">G</span> <span class="p">[</span><span class="n">H</span><span class="p">]</span> <span class="n">dip</span> <span class="n">F</span>
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||||
</pre></div>
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</div>
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<p>Plug it in and convert to genrec.</p>
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||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">H</span> <span class="o">==</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="n">c</span><span class="p">]</span> <span class="p">[</span><span class="n">G</span> <span class="p">[</span><span class="n">H</span><span class="p">]</span> <span class="n">dip</span> <span class="n">F</span><span class="p">]</span> <span class="n">ifte</span>
|
||||
<span class="n">H</span> <span class="o">==</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="n">c</span><span class="p">]</span> <span class="p">[</span><span class="n">G</span><span class="p">]</span> <span class="p">[</span><span class="n">dip</span> <span class="n">F</span><span class="p">]</span> <span class="n">genrec</span>
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||||
</pre></div>
|
||||
</div>
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||||
<p>This is the form of a hylomorphism in Joy, which nicely illustrates that
|
||||
it is a simple specialization of the general recursion combinator.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">H</span> <span class="o">==</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="n">c</span> <span class="p">[</span><span class="n">G</span><span class="p">]</span> <span class="p">[</span><span class="n">F</span><span class="p">]</span> <span class="n">hylomorphism</span> <span class="o">==</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="n">c</span><span class="p">]</span> <span class="p">[</span><span class="n">G</span><span class="p">]</span> <span class="p">[</span><span class="n">dip</span> <span class="n">F</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="derivation-of-hylomorphism-combinator">
|
||||
<h2>Derivation of <code class="docutils literal notranslate"><span class="pre">hylomorphism</span></code> combinator<a class="headerlink" href="#derivation-of-hylomorphism-combinator" title="Permalink to this headline">¶</a></h2>
|
||||
<p>Now we just need to derive a definition that builds the <code class="docutils literal notranslate"><span class="pre">genrec</span></code>
|
||||
arguments out of the pieces given to the <code class="docutils literal notranslate"><span class="pre">hylomorphism</span></code> combinator.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="n">c</span> <span class="p">[</span><span class="n">G</span><span class="p">]</span> <span class="p">[</span><span class="n">F</span><span class="p">]</span> <span class="n">hylomorphism</span>
|
||||
<span class="o">------------------------------------------</span>
|
||||
<span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="n">c</span><span class="p">]</span> <span class="p">[</span><span class="n">G</span><span class="p">]</span> <span class="p">[</span><span class="n">dip</span> <span class="n">F</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Working in reverse:</p>
|
||||
<ul class="simple">
|
||||
<li>Use <code class="docutils literal notranslate"><span class="pre">swoncat</span></code> twice to decouple <code class="docutils literal notranslate"><span class="pre">[c]</span></code> and <code class="docutils literal notranslate"><span class="pre">[F]</span></code>.</li>
|
||||
<li>Use <code class="docutils literal notranslate"><span class="pre">unit</span></code> to dequote <code class="docutils literal notranslate"><span class="pre">c</span></code>.</li>
|
||||
<li>Use <code class="docutils literal notranslate"><span class="pre">dipd</span></code> to untangle <code class="docutils literal notranslate"><span class="pre">[unit</span> <span class="pre">[pop]</span> <span class="pre">swoncat]</span></code> from the givens.</li>
|
||||
</ul>
|
||||
<p>So:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">H</span> <span class="o">==</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="n">c</span><span class="p">]</span> <span class="p">[</span><span class="n">G</span><span class="p">]</span> <span class="p">[</span><span class="n">dip</span> <span class="n">F</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">c</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span><span class="p">]</span> <span class="n">swoncat</span> <span class="p">[</span><span class="n">G</span><span class="p">]</span> <span class="p">[</span><span class="n">F</span><span class="p">]</span> <span class="p">[</span><span class="n">dip</span><span class="p">]</span> <span class="n">swoncat</span> <span class="n">genrec</span>
|
||||
<span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="n">c</span> <span class="n">unit</span> <span class="p">[</span><span class="n">pop</span><span class="p">]</span> <span class="n">swoncat</span> <span class="p">[</span><span class="n">G</span><span class="p">]</span> <span class="p">[</span><span class="n">F</span><span class="p">]</span> <span class="p">[</span><span class="n">dip</span><span class="p">]</span> <span class="n">swoncat</span> <span class="n">genrec</span>
|
||||
<span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="n">c</span> <span class="p">[</span><span class="n">G</span><span class="p">]</span> <span class="p">[</span><span class="n">F</span><span class="p">]</span> <span class="p">[</span><span class="n">unit</span> <span class="p">[</span><span class="n">pop</span><span class="p">]</span> <span class="n">swoncat</span><span class="p">]</span> <span class="n">dipd</span> <span class="p">[</span><span class="n">dip</span><span class="p">]</span> <span class="n">swoncat</span> <span class="n">genrec</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>At this point all of the arguments (givens) to the hylomorphism are to
|
||||
the left so we have a definition for <code class="docutils literal notranslate"><span class="pre">hylomorphism</span></code>:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">hylomorphism</span> <span class="o">==</span> <span class="p">[</span><span class="n">unit</span> <span class="p">[</span><span class="n">pop</span><span class="p">]</span> <span class="n">swoncat</span><span class="p">]</span> <span class="n">dipd</span> <span class="p">[</span><span class="n">dip</span><span class="p">]</span> <span class="n">swoncat</span> <span class="n">genrec</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">define</span><span class="p">(</span><span class="s1">'hylomorphism == [unit [pop] swoncat] dipd [dip] swoncat genrec'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="section" id="example-finding-triangular-numbers">
|
||||
<h3>Example: Finding <a class="reference external" href="https://en.wikipedia.org/wiki/Triangular_number">Triangular Numbers</a><a class="headerlink" href="#example-finding-triangular-numbers" title="Permalink to this headline">¶</a></h3>
|
||||
<p>Let’s write a function that, given a positive integer, returns the sum
|
||||
of all positive integers less than that one. (In this case the types
|
||||
<code class="docutils literal notranslate"><span class="pre">A</span></code>, <code class="docutils literal notranslate"><span class="pre">B</span></code> and <code class="docutils literal notranslate"><span class="pre">C</span></code> are all <code class="docutils literal notranslate"><span class="pre">int</span></code>.)</p>
|
||||
<p>To sum a range of integers from 0 to <em>n</em> - 1:</p>
|
||||
<ul class="simple">
|
||||
<li><code class="docutils literal notranslate"><span class="pre">[P]</span></code> is <code class="docutils literal notranslate"><span class="pre">[1</span> <span class="pre"><=]</span></code></li>
|
||||
<li><code class="docutils literal notranslate"><span class="pre">c</span></code> is <code class="docutils literal notranslate"><span class="pre">0</span></code></li>
|
||||
<li><code class="docutils literal notranslate"><span class="pre">[G]</span></code> is <code class="docutils literal notranslate"><span class="pre">[--</span> <span class="pre">dup]</span></code></li>
|
||||
<li><code class="docutils literal notranslate"><span class="pre">[F]</span></code> is <code class="docutils literal notranslate"><span class="pre">[+]</span></code></li>
|
||||
</ul>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">define</span><span class="p">(</span><span class="s1">'triangular_number == [1 <=] 0 [-- dup] [+] hylomorphism'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Let’s try it:</p>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'5 triangular_number'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">10</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[0 1 2 3 4 5 6] [triangular_number] map'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="mi">0</span> <span class="mi">0</span> <span class="mi">1</span> <span class="mi">3</span> <span class="mi">6</span> <span class="mi">10</span> <span class="mi">15</span><span class="p">]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="four-specializations">
|
||||
<h2>Four Specializations<a class="headerlink" href="#four-specializations" title="Permalink to this headline">¶</a></h2>
|
||||
<p>There are at least four kinds of recursive combinator, depending on two
|
||||
choices. The first choice is whether the combiner function <code class="docutils literal notranslate"><span class="pre">F</span></code> should
|
||||
be evaluated during the recursion or pushed into the pending expression
|
||||
to be “collapsed” at the end. The second choice is whether the combiner
|
||||
needs to operate on the current value of the datastructure or the
|
||||
generator’s output, in other words, whether <code class="docutils literal notranslate"><span class="pre">F</span></code> or <code class="docutils literal notranslate"><span class="pre">G</span></code> should run
|
||||
first in the recursive branch.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">H1</span> <span class="o">==</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="n">c</span><span class="p">]</span> <span class="p">[</span><span class="n">G</span> <span class="p">]</span> <span class="p">[</span><span class="n">dip</span> <span class="n">F</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="n">H2</span> <span class="o">==</span> <span class="n">c</span> <span class="n">swap</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span><span class="p">]</span> <span class="p">[</span><span class="n">G</span> <span class="p">[</span><span class="n">F</span><span class="p">]</span> <span class="n">dip</span> <span class="p">]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="n">H3</span> <span class="o">==</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="n">c</span><span class="p">]</span> <span class="p">[</span> <span class="p">[</span><span class="n">G</span><span class="p">]</span> <span class="n">dupdip</span> <span class="p">]</span> <span class="p">[</span><span class="n">dip</span> <span class="n">F</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="n">H4</span> <span class="o">==</span> <span class="n">c</span> <span class="n">swap</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span><span class="p">]</span> <span class="p">[</span> <span class="p">[</span><span class="n">F</span><span class="p">]</span> <span class="n">dupdip</span> <span class="n">G</span><span class="p">]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>The working of the generator function <code class="docutils literal notranslate"><span class="pre">G</span></code> differs slightly for each.
|
||||
Consider the recursive branches:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>... a G [H1] dip F w/ a G == a′ b
|
||||
|
||||
... c a G [F] dip H2 a G == b a′
|
||||
|
||||
... a [G] dupdip [H3] dip F a G == a′
|
||||
|
||||
... c a [F] dupdip G H4 a G == a′
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>The following four sections illustrate how these work, omitting the
|
||||
predicate evaluation.</p>
|
||||
<div class="section" id="h1">
|
||||
<h3><code class="docutils literal notranslate"><span class="pre">H1</span></code><a class="headerlink" href="#h1" title="Permalink to this headline">¶</a></h3>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">H1</span> <span class="o">==</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="n">c</span><span class="p">]</span> <span class="p">[</span><span class="n">G</span><span class="p">]</span> <span class="p">[</span><span class="n">dip</span> <span class="n">F</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Iterate n times.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>... a G [H1] dip F
|
||||
... a′ b [H1] dip F
|
||||
... a′ H1 b F
|
||||
... a′ G [H1] dip F b F
|
||||
... a″ b′ [H1] dip F b F
|
||||
... a″ H1 b′ F b F
|
||||
... a″ G [H1] dip F b′ F b F
|
||||
... a‴ b″ [H1] dip F b′ F b F
|
||||
... a‴ H1 b″ F b′ F b F
|
||||
... a‴ pop c b″ F b′ F b F
|
||||
... c b″ F b′ F b F
|
||||
... d b′ F b F
|
||||
... d′ b F
|
||||
... d″
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>This form builds up a pending expression (continuation) that contains
|
||||
the intermediate results along with the pending combiner functions. When
|
||||
the base case is reached the last term is replaced by the identity value
|
||||
<code class="docutils literal notranslate"><span class="pre">c</span></code> and the continuation “collapses” into the final result using the
|
||||
combiner <code class="docutils literal notranslate"><span class="pre">F</span></code>.</p>
|
||||
</div>
|
||||
<div class="section" id="h2">
|
||||
<h3><code class="docutils literal notranslate"><span class="pre">H2</span></code><a class="headerlink" href="#h2" title="Permalink to this headline">¶</a></h3>
|
||||
<p>When you can start with the identity value <code class="docutils literal notranslate"><span class="pre">c</span></code> on the stack and the
|
||||
combiner <code class="docutils literal notranslate"><span class="pre">F</span></code> can operate as you go using the intermediate results
|
||||
immediately rather than queuing them up, use this form. An important
|
||||
difference is that the generator function must return its results in the
|
||||
reverse order.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>H2 == c swap [P] [pop] [G [F] dip] primrec
|
||||
|
||||
... c a G [F] dip H2
|
||||
... c b a′ [F] dip H2
|
||||
... c b F a′ H2
|
||||
... d a′ H2
|
||||
... d a′ G [F] dip H2
|
||||
... d b′ a″ [F] dip H2
|
||||
... d b′ F a″ H2
|
||||
... d′ a″ H2
|
||||
... d′ a″ G [F] dip H2
|
||||
... d′ b″ a‴ [F] dip H2
|
||||
... d′ b″ F a‴ H2
|
||||
... d″ a‴ H2
|
||||
... d″ a‴ pop
|
||||
... d″
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="h3">
|
||||
<h3><code class="docutils literal notranslate"><span class="pre">H3</span></code><a class="headerlink" href="#h3" title="Permalink to this headline">¶</a></h3>
|
||||
<p>If you examine the traces above you’ll see that the combiner <code class="docutils literal notranslate"><span class="pre">F</span></code> only
|
||||
gets to operate on the results of <code class="docutils literal notranslate"><span class="pre">G</span></code>, it never “sees” the first value
|
||||
<code class="docutils literal notranslate"><span class="pre">a</span></code>. If the combiner and the generator both need to work on the
|
||||
current value then <code class="docutils literal notranslate"><span class="pre">dup</span></code> must be used, and the generator must produce
|
||||
one item instead of two (the b is instead the duplicate of a.)</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>H3 == [P] [pop c] [[G] dupdip] [dip F] genrec
|
||||
|
||||
... a [G] dupdip [H3] dip F
|
||||
... a G a [H3] dip F
|
||||
... a′ a [H3] dip F
|
||||
... a′ H3 a F
|
||||
... a′ [G] dupdip [H3] dip F a F
|
||||
... a′ G a′ [H3] dip F a F
|
||||
... a″ a′ [H3] dip F a F
|
||||
... a″ H3 a′ F a F
|
||||
... a″ [G] dupdip [H3] dip F a′ F a F
|
||||
... a″ G a″ [H3] dip F a′ F a F
|
||||
... a‴ a″ [H3] dip F a′ F a F
|
||||
... a‴ H3 a″ F a′ F a F
|
||||
... a‴ pop c a″ F a′ F a F
|
||||
... c a″ F a′ F a F
|
||||
... d a′ F a F
|
||||
... d′ a F
|
||||
... d″
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="h4">
|
||||
<h3><code class="docutils literal notranslate"><span class="pre">H4</span></code><a class="headerlink" href="#h4" title="Permalink to this headline">¶</a></h3>
|
||||
<p>And, last but not least, if you can combine as you go, starting with
|
||||
<code class="docutils literal notranslate"><span class="pre">c</span></code>, and the combiner <code class="docutils literal notranslate"><span class="pre">F</span></code> needs to work on the current item, this is
|
||||
the form:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>H4 == c swap [P] [pop] [[F] dupdip G] primrec
|
||||
|
||||
... c a [F] dupdip G H4
|
||||
... c a F a G H4
|
||||
... d a G H4
|
||||
... d a′ H4
|
||||
... d a′ [F] dupdip G H4
|
||||
... d a′ F a′ G H4
|
||||
... d′ a′ G H4
|
||||
... d′ a″ H4
|
||||
... d′ a″ [F] dupdip G H4
|
||||
... d′ a″ F a″ G H4
|
||||
... d″ a″ G H4
|
||||
... d″ a‴ H4
|
||||
... d″ a‴ pop
|
||||
... d″
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="anamorphism">
|
||||
<h2>Anamorphism<a class="headerlink" href="#anamorphism" title="Permalink to this headline">¶</a></h2>
|
||||
<p>An anamorphism can be defined as a hylomorphism that uses <code class="docutils literal notranslate"><span class="pre">[]</span></code> for
|
||||
<code class="docutils literal notranslate"><span class="pre">c</span></code> and <code class="docutils literal notranslate"><span class="pre">swons</span></code> for <code class="docutils literal notranslate"><span class="pre">F</span></code>. An anamorphic function builds a list of
|
||||
values.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">A</span> <span class="o">==</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[]</span> <span class="p">[</span><span class="n">G</span><span class="p">]</span> <span class="p">[</span><span class="n">swons</span><span class="p">]</span> <span class="n">hylomorphism</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="section" id="range-et-al">
|
||||
<h3><code class="docutils literal notranslate"><span class="pre">range</span></code> et. al.<a class="headerlink" href="#range-et-al" title="Permalink to this headline">¶</a></h3>
|
||||
<p>An example of an anamorphism is the <code class="docutils literal notranslate"><span class="pre">range</span></code> function which generates
|
||||
the list of integers from 0 to <em>n</em> - 1 given <em>n</em>.</p>
|
||||
<p>Each of the above variations can be used to make four slightly different
|
||||
<code class="docutils literal notranslate"><span class="pre">range</span></code> functions.</p>
|
||||
<div class="section" id="range-with-h1">
|
||||
<h4><code class="docutils literal notranslate"><span class="pre">range</span></code> with <code class="docutils literal notranslate"><span class="pre">H1</span></code><a class="headerlink" href="#range-with-h1" title="Permalink to this headline">¶</a></h4>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">H1</span> <span class="o">==</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="n">c</span><span class="p">]</span> <span class="p">[</span><span class="n">G</span><span class="p">]</span> <span class="p">[</span><span class="n">dip</span> <span class="n">F</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="o">==</span> <span class="p">[</span><span class="mi">0</span> <span class="o"><=</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="p">[]]</span> <span class="p">[</span><span class="o">--</span> <span class="n">dup</span><span class="p">]</span> <span class="p">[</span><span class="n">dip</span> <span class="n">swons</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">define</span><span class="p">(</span><span class="s1">'range == [0 <=] [] [-- dup] [swons] hylomorphism'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'5 range'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="mi">4</span> <span class="mi">3</span> <span class="mi">2</span> <span class="mi">1</span> <span class="mi">0</span><span class="p">]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="range-with-h2">
|
||||
<h4><code class="docutils literal notranslate"><span class="pre">range</span></code> with <code class="docutils literal notranslate"><span class="pre">H2</span></code><a class="headerlink" href="#range-with-h2" title="Permalink to this headline">¶</a></h4>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">H2</span> <span class="o">==</span> <span class="n">c</span> <span class="n">swap</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span><span class="p">]</span> <span class="p">[</span><span class="n">G</span> <span class="p">[</span><span class="n">F</span><span class="p">]</span> <span class="n">dip</span><span class="p">]</span> <span class="n">primrec</span>
|
||||
<span class="o">==</span> <span class="p">[]</span> <span class="n">swap</span> <span class="p">[</span><span class="mi">0</span> <span class="o"><=</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span><span class="p">]</span> <span class="p">[</span><span class="o">--</span> <span class="n">dup</span> <span class="p">[</span><span class="n">swons</span><span class="p">]</span> <span class="n">dip</span><span class="p">]</span> <span class="n">primrec</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">define</span><span class="p">(</span><span class="s1">'range_reverse == [] swap [0 <=] [pop] [-- dup [swons] dip] primrec'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'5 range_reverse'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="mi">0</span> <span class="mi">1</span> <span class="mi">2</span> <span class="mi">3</span> <span class="mi">4</span><span class="p">]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="range-with-h3">
|
||||
<h4><code class="docutils literal notranslate"><span class="pre">range</span></code> with <code class="docutils literal notranslate"><span class="pre">H3</span></code><a class="headerlink" href="#range-with-h3" title="Permalink to this headline">¶</a></h4>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">H3</span> <span class="o">==</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="n">c</span><span class="p">]</span> <span class="p">[[</span><span class="n">G</span><span class="p">]</span> <span class="n">dupdip</span><span class="p">]</span> <span class="p">[</span><span class="n">dip</span> <span class="n">F</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="o">==</span> <span class="p">[</span><span class="mi">0</span> <span class="o"><=</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="p">[]]</span> <span class="p">[[</span><span class="o">--</span><span class="p">]</span> <span class="n">dupdip</span><span class="p">]</span> <span class="p">[</span><span class="n">dip</span> <span class="n">swons</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">define</span><span class="p">(</span><span class="s1">'ranger == [0 <=] [pop []] [[--] dupdip] [dip swons] genrec'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'5 ranger'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="mi">5</span> <span class="mi">4</span> <span class="mi">3</span> <span class="mi">2</span> <span class="mi">1</span><span class="p">]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="range-with-h4">
|
||||
<h4><code class="docutils literal notranslate"><span class="pre">range</span></code> with <code class="docutils literal notranslate"><span class="pre">H4</span></code><a class="headerlink" href="#range-with-h4" title="Permalink to this headline">¶</a></h4>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">H4</span> <span class="o">==</span> <span class="n">c</span> <span class="n">swap</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span><span class="p">]</span> <span class="p">[[</span><span class="n">F</span><span class="p">]</span> <span class="n">dupdip</span> <span class="n">G</span> <span class="p">]</span> <span class="n">primrec</span>
|
||||
<span class="o">==</span> <span class="p">[]</span> <span class="n">swap</span> <span class="p">[</span><span class="mi">0</span> <span class="o"><=</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span><span class="p">]</span> <span class="p">[[</span><span class="n">swons</span><span class="p">]</span> <span class="n">dupdip</span> <span class="o">--</span><span class="p">]</span> <span class="n">primrec</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">define</span><span class="p">(</span><span class="s1">'ranger_reverse == [] swap [0 <=] [pop] [[swons] dupdip --] primrec'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'5 ranger_reverse'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="mi">1</span> <span class="mi">2</span> <span class="mi">3</span> <span class="mi">4</span> <span class="mi">5</span><span class="p">]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Hopefully this illustrates the workings of the variations. For more
|
||||
insight you can run the cells using the <code class="docutils literal notranslate"><span class="pre">V()</span></code> function instead of the
|
||||
<code class="docutils literal notranslate"><span class="pre">J()</span></code> function to get a trace of the Joy evaluation.</p>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="catamorphism">
|
||||
<h2>Catamorphism<a class="headerlink" href="#catamorphism" title="Permalink to this headline">¶</a></h2>
|
||||
<p>A catamorphism can be defined as a hylomorphism that uses
|
||||
<code class="docutils literal notranslate"><span class="pre">[uncons</span> <span class="pre">swap]</span></code> for <code class="docutils literal notranslate"><span class="pre">[G]</span></code> and <code class="docutils literal notranslate"><span class="pre">[[]</span> <span class="pre">=]</span></code> (or just <code class="docutils literal notranslate"><span class="pre">[not]</span></code>) for the
|
||||
predicate <code class="docutils literal notranslate"><span class="pre">[P]</span></code>. A catamorphic function tears down a list term-by-term
|
||||
and makes some new value.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">C</span> <span class="o">==</span> <span class="p">[</span><span class="ow">not</span><span class="p">]</span> <span class="n">c</span> <span class="p">[</span><span class="n">uncons</span> <span class="n">swap</span><span class="p">]</span> <span class="p">[</span><span class="n">F</span><span class="p">]</span> <span class="n">hylomorphism</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">define</span><span class="p">(</span><span class="s1">'swuncons == uncons swap'</span><span class="p">)</span> <span class="c1"># Awkward name.</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>An example of a catamorphism is the sum function.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="nb">sum</span> <span class="o">==</span> <span class="p">[</span><span class="ow">not</span><span class="p">]</span> <span class="mi">0</span> <span class="p">[</span><span class="n">swuncons</span><span class="p">]</span> <span class="p">[</span><span class="o">+</span><span class="p">]</span> <span class="n">hylomorphism</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">define</span><span class="p">(</span><span class="s1">'sum == [not] 0 [swuncons] [+] hylomorphism'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[5 4 3 2 1] sum'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">15</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="section" id="the-step-combinator">
|
||||
<h3>The <code class="docutils literal notranslate"><span class="pre">step</span></code> combinator<a class="headerlink" href="#the-step-combinator" title="Permalink to this headline">¶</a></h3>
|
||||
<p>The <code class="docutils literal notranslate"><span class="pre">step</span></code> combinator will usually be better to use than
|
||||
<code class="docutils literal notranslate"><span class="pre">catamorphism</span></code>.</p>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[step] help'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">Run</span> <span class="n">a</span> <span class="n">quoted</span> <span class="n">program</span> <span class="n">on</span> <span class="n">each</span> <span class="n">item</span> <span class="ow">in</span> <span class="n">a</span> <span class="n">sequence</span><span class="o">.</span>
|
||||
<span class="p">::</span>
|
||||
|
||||
<span class="o">...</span> <span class="p">[]</span> <span class="p">[</span><span class="n">Q</span><span class="p">]</span> <span class="o">.</span> <span class="n">step</span>
|
||||
<span class="o">-----------------------</span>
|
||||
<span class="o">...</span> <span class="o">.</span>
|
||||
|
||||
|
||||
<span class="o">...</span> <span class="p">[</span><span class="n">a</span><span class="p">]</span> <span class="p">[</span><span class="n">Q</span><span class="p">]</span> <span class="o">.</span> <span class="n">step</span>
|
||||
<span class="o">------------------------</span>
|
||||
<span class="o">...</span> <span class="n">a</span> <span class="o">.</span> <span class="n">Q</span>
|
||||
|
||||
|
||||
<span class="o">...</span> <span class="p">[</span><span class="n">a</span> <span class="n">b</span> <span class="n">c</span><span class="p">]</span> <span class="p">[</span><span class="n">Q</span><span class="p">]</span> <span class="o">.</span> <span class="n">step</span>
|
||||
<span class="o">----------------------------------------</span>
|
||||
<span class="o">...</span> <span class="n">a</span> <span class="o">.</span> <span class="n">Q</span> <span class="p">[</span><span class="n">b</span> <span class="n">c</span><span class="p">]</span> <span class="p">[</span><span class="n">Q</span><span class="p">]</span> <span class="n">step</span>
|
||||
|
||||
<span class="n">The</span> <span class="n">step</span> <span class="n">combinator</span> <span class="n">executes</span> <span class="n">the</span> <span class="n">quotation</span> <span class="n">on</span> <span class="n">each</span> <span class="n">member</span> <span class="n">of</span> <span class="n">the</span> <span class="nb">list</span>
|
||||
<span class="n">on</span> <span class="n">top</span> <span class="n">of</span> <span class="n">the</span> <span class="n">stack</span><span class="o">.</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">define</span><span class="p">(</span><span class="s1">'sum == 0 swap [+] step'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[5 4 3 2 1] sum'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">15</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="example-factorial-function">
|
||||
<h2>Example: Factorial Function<a class="headerlink" href="#example-factorial-function" title="Permalink to this headline">¶</a></h2>
|
||||
<p>For the Factorial function:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">H4</span> <span class="o">==</span> <span class="n">c</span> <span class="n">swap</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span><span class="p">]</span> <span class="p">[[</span><span class="n">F</span><span class="p">]</span> <span class="n">dupdip</span> <span class="n">G</span><span class="p">]</span> <span class="n">primrec</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>With:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">c</span> <span class="o">==</span> <span class="mi">1</span>
|
||||
<span class="n">F</span> <span class="o">==</span> <span class="o">*</span>
|
||||
<span class="n">G</span> <span class="o">==</span> <span class="o">--</span>
|
||||
<span class="n">P</span> <span class="o">==</span> <span class="mi">1</span> <span class="o"><=</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">define</span><span class="p">(</span><span class="s1">'factorial == 1 swap [1 <=] [pop] [[*] dupdip --] primrec'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'5 factorial'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">120</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="example-tails">
|
||||
<h2>Example: <code class="docutils literal notranslate"><span class="pre">tails</span></code><a class="headerlink" href="#example-tails" title="Permalink to this headline">¶</a></h2>
|
||||
<p>An example of a paramorphism for lists given in the <a class="reference external" href="http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.41.125">“Bananas…”
|
||||
paper</a>
|
||||
is <code class="docutils literal notranslate"><span class="pre">tails</span></code> which returns the list of “tails” of a list.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span> <span class="p">[</span><span class="mi">1</span> <span class="mi">2</span> <span class="mi">3</span><span class="p">]</span> <span class="n">tails</span>
|
||||
<span class="o">--------------------</span>
|
||||
<span class="p">[[]</span> <span class="p">[</span><span class="mi">3</span><span class="p">]</span> <span class="p">[</span><span class="mi">2</span> <span class="mi">3</span><span class="p">]]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>We can build as we go, and we want <code class="docutils literal notranslate"><span class="pre">F</span></code> to run after <code class="docutils literal notranslate"><span class="pre">G</span></code>, so we use
|
||||
pattern <code class="docutils literal notranslate"><span class="pre">H2</span></code>:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">H2</span> <span class="o">==</span> <span class="n">c</span> <span class="n">swap</span> <span class="p">[</span><span class="n">P</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span><span class="p">]</span> <span class="p">[</span><span class="n">G</span> <span class="p">[</span><span class="n">F</span><span class="p">]</span> <span class="n">dip</span><span class="p">]</span> <span class="n">primrec</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>We would use:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">c</span> <span class="o">==</span> <span class="p">[]</span>
|
||||
<span class="n">F</span> <span class="o">==</span> <span class="n">swons</span>
|
||||
<span class="n">G</span> <span class="o">==</span> <span class="n">rest</span> <span class="n">dup</span>
|
||||
<span class="n">P</span> <span class="o">==</span> <span class="ow">not</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">define</span><span class="p">(</span><span class="s1">'tails == [] swap [not] [pop] [rest dup [swons] dip] primrec'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[1 2 3] tails'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[[]</span> <span class="p">[</span><span class="mi">3</span><span class="p">]</span> <span class="p">[</span><span class="mi">2</span> <span class="mi">3</span><span class="p">]]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="conclusion-patterns-of-recursion">
|
||||
<h2>Conclusion: Patterns of Recursion<a class="headerlink" href="#conclusion-patterns-of-recursion" title="Permalink to this headline">¶</a></h2>
|
||||
<p>Our story so far…</p>
|
||||
<div class="section" id="hylo-ana-cata">
|
||||
<h3>Hylo-, Ana-, Cata-<a class="headerlink" href="#hylo-ana-cata" title="Permalink to this headline">¶</a></h3>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">H</span> <span class="o">==</span> <span class="p">[</span><span class="n">P</span> <span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="n">c</span> <span class="p">]</span> <span class="p">[</span><span class="n">G</span> <span class="p">]</span> <span class="p">[</span><span class="n">dip</span> <span class="n">F</span> <span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="n">A</span> <span class="o">==</span> <span class="p">[</span><span class="n">P</span> <span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="p">[]]</span> <span class="p">[</span><span class="n">G</span> <span class="p">]</span> <span class="p">[</span><span class="n">dip</span> <span class="n">swap</span> <span class="n">cons</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="n">C</span> <span class="o">==</span> <span class="p">[</span><span class="ow">not</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="n">c</span> <span class="p">]</span> <span class="p">[</span><span class="n">uncons</span> <span class="n">swap</span><span class="p">]</span> <span class="p">[</span><span class="n">dip</span> <span class="n">F</span> <span class="p">]</span> <span class="n">genrec</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="para">
|
||||
<h3>Para-, ?-, ?-<a class="headerlink" href="#para" title="Permalink to this headline">¶</a></h3>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>P == c swap [P ] [pop] [[F ] dupdip G ] primrec
|
||||
? == [] swap [P ] [pop] [[swap cons] dupdip G ] primrec
|
||||
? == c swap [not] [pop] [[F ] dupdip uncons swap] primrec
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="appendix-fun-with-symbols">
|
||||
<h2>Appendix: Fun with Symbols<a class="headerlink" href="#appendix-fun-with-symbols" title="Permalink to this headline">¶</a></h2>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>|[ (c, F), (G, P) ]| == (|c, F|) • [(G, P)]
|
||||
</pre></div>
|
||||
</div>
|
||||
<p><a class="reference external" href="http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.41.125">“Bananas, Lenses, & Barbed
|
||||
Wire”</a></p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">(</span><span class="o">|...|</span><span class="p">)</span> <span class="p">[(</span><span class="o">...</span><span class="p">)]</span> <span class="p">[</span><span class="o"><...></span><span class="p">]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>I think they are having slightly too much fun with the symbols. However,
|
||||
“Too much is always better than not enough.”</p>
|
||||
</div>
|
||||
</div>
|
||||
|
||||
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="sphinxsidebar" role="navigation" aria-label="main navigation">
|
||||
<div class="sphinxsidebarwrapper">
|
||||
<h3><a href="../index.html">Table Of Contents</a></h3>
|
||||
<ul>
|
||||
<li><a class="reference internal" href="#">Recursive Combinators</a><ul>
|
||||
<li><a class="reference internal" href="#designing-recursive-functions">Designing Recursive Functions</a></li>
|
||||
<li><a class="reference internal" href="#primitive-recursive-functions">Primitive Recursive Functions</a></li>
|
||||
<li><a class="reference internal" href="#hylomorphism">Hylomorphism</a></li>
|
||||
<li><a class="reference internal" href="#hylomorphism-in-joy">Hylomorphism in Joy</a></li>
|
||||
<li><a class="reference internal" href="#derivation-of-hylomorphism-combinator">Derivation of <code class="docutils literal notranslate"><span class="pre">hylomorphism</span></code> combinator</a><ul>
|
||||
<li><a class="reference internal" href="#example-finding-triangular-numbers">Example: Finding Triangular Numbers</a></li>
|
||||
</ul>
|
||||
</li>
|
||||
<li><a class="reference internal" href="#four-specializations">Four Specializations</a><ul>
|
||||
<li><a class="reference internal" href="#h1"><code class="docutils literal notranslate"><span class="pre">H1</span></code></a></li>
|
||||
<li><a class="reference internal" href="#h2"><code class="docutils literal notranslate"><span class="pre">H2</span></code></a></li>
|
||||
<li><a class="reference internal" href="#h3"><code class="docutils literal notranslate"><span class="pre">H3</span></code></a></li>
|
||||
<li><a class="reference internal" href="#h4"><code class="docutils literal notranslate"><span class="pre">H4</span></code></a></li>
|
||||
</ul>
|
||||
</li>
|
||||
<li><a class="reference internal" href="#anamorphism">Anamorphism</a><ul>
|
||||
<li><a class="reference internal" href="#range-et-al"><code class="docutils literal notranslate"><span class="pre">range</span></code> et. al.</a><ul>
|
||||
<li><a class="reference internal" href="#range-with-h1"><code class="docutils literal notranslate"><span class="pre">range</span></code> with <code class="docutils literal notranslate"><span class="pre">H1</span></code></a></li>
|
||||
<li><a class="reference internal" href="#range-with-h2"><code class="docutils literal notranslate"><span class="pre">range</span></code> with <code class="docutils literal notranslate"><span class="pre">H2</span></code></a></li>
|
||||
<li><a class="reference internal" href="#range-with-h3"><code class="docutils literal notranslate"><span class="pre">range</span></code> with <code class="docutils literal notranslate"><span class="pre">H3</span></code></a></li>
|
||||
<li><a class="reference internal" href="#range-with-h4"><code class="docutils literal notranslate"><span class="pre">range</span></code> with <code class="docutils literal notranslate"><span class="pre">H4</span></code></a></li>
|
||||
</ul>
|
||||
</li>
|
||||
</ul>
|
||||
</li>
|
||||
<li><a class="reference internal" href="#catamorphism">Catamorphism</a><ul>
|
||||
<li><a class="reference internal" href="#the-step-combinator">The <code class="docutils literal notranslate"><span class="pre">step</span></code> combinator</a></li>
|
||||
</ul>
|
||||
</li>
|
||||
<li><a class="reference internal" href="#example-factorial-function">Example: Factorial Function</a></li>
|
||||
<li><a class="reference internal" href="#example-tails">Example: <code class="docutils literal notranslate"><span class="pre">tails</span></code></a></li>
|
||||
<li><a class="reference internal" href="#conclusion-patterns-of-recursion">Conclusion: Patterns of Recursion</a><ul>
|
||||
<li><a class="reference internal" href="#hylo-ana-cata">Hylo-, Ana-, Cata-</a></li>
|
||||
<li><a class="reference internal" href="#para">Para-, ?-, ?-</a></li>
|
||||
</ul>
|
||||
</li>
|
||||
<li><a class="reference internal" href="#appendix-fun-with-symbols">Appendix: Fun with Symbols</a></li>
|
||||
</ul>
|
||||
</li>
|
||||
</ul>
|
||||
<div class="relations">
|
||||
<h3>Related Topics</h3>
|
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|
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|
||||
<li><a href="index.html">Essays about Programming in Joy</a><ul>
|
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<li>Previous: <a href="Replacing.html" title="previous chapter">Replacing Functions in the Dictionary</a></li>
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<span xmlns:dct="http://purl.org/dc/terms/" property="dct:title">Thun Documentation</span> by <a xmlns:cc="http://creativecommons.org/ns#" href="https://joypy.osdn.io/" property="cc:attributionName" rel="cc:attributionURL">Simon Forman</a> is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License</a>.<br />Based on a work at <a xmlns:dct="http://purl.org/dc/terms/" href="https://osdn.net/projects/joypy/" rel="dct:source">https://osdn.net/projects/joypy/</a>.
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<div class="section" id="replacing-functions-in-the-dictionary">
|
||||
<h1>Replacing Functions in the Dictionary<a class="headerlink" href="#replacing-functions-in-the-dictionary" title="Permalink to this headline">¶</a></h1>
|
||||
<p>For now, there is no way to define new functions from within the Joy
|
||||
language. All functions (and the interpreter) all accept and return a
|
||||
dictionary parameter (in addition to the stack and expression) so that
|
||||
we can implement e.g. a function that adds new functions to the
|
||||
dictionary. However, there’s no function that does that. Adding a new
|
||||
function to the dictionary is a meta-interpreter action, you have to do
|
||||
it in Python, not Joy.</p>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">notebook_preamble</span> <span class="k">import</span> <span class="n">D</span><span class="p">,</span> <span class="n">J</span><span class="p">,</span> <span class="n">V</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="section" id="a-long-trace">
|
||||
<h2>A long trace<a class="headerlink" href="#a-long-trace" title="Permalink to this headline">¶</a></h2>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">V</span><span class="p">(</span><span class="s1">'[23 18] average'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span> <span class="o">.</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="n">average</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="o">.</span> <span class="n">average</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="o">.</span> <span class="p">[</span><span class="nb">sum</span> <span class="mf">1.0</span> <span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">size</span><span class="p">]</span> <span class="n">cleave</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="nb">sum</span> <span class="mf">1.0</span> <span class="o">*</span><span class="p">]</span> <span class="o">.</span> <span class="p">[</span><span class="n">size</span><span class="p">]</span> <span class="n">cleave</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="nb">sum</span> <span class="mf">1.0</span> <span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">size</span><span class="p">]</span> <span class="o">.</span> <span class="n">cleave</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="nb">sum</span> <span class="mf">1.0</span> <span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">size</span><span class="p">]</span> <span class="o">.</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">app2</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="nb">sum</span> <span class="mf">1.0</span> <span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">.</span> <span class="n">app2</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[[</span><span class="nb">sum</span> <span class="mf">1.0</span> <span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">.</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="nb">sum</span> <span class="mf">1.0</span> <span class="o">*</span><span class="p">]</span> <span class="o">.</span> <span class="n">i</span> <span class="p">[[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="o">.</span> <span class="nb">sum</span> <span class="mf">1.0</span> <span class="o">*</span> <span class="p">[[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">41</span> <span class="o">.</span> <span class="mf">1.0</span> <span class="o">*</span> <span class="p">[[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">41</span> <span class="mf">1.0</span> <span class="o">.</span> <span class="o">*</span> <span class="p">[[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mf">41.0</span> <span class="o">.</span> <span class="p">[[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mf">41.0</span> <span class="p">[[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="o">.</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="mf">41.0</span><span class="p">]</span> <span class="o">.</span> <span class="n">first</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="mf">41.0</span> <span class="o">.</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="mf">41.0</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="o">.</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="mf">41.0</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">.</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="n">size</span><span class="p">]</span> <span class="o">.</span> <span class="n">i</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="o">.</span> <span class="n">size</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="o">.</span> <span class="mi">0</span> <span class="n">swap</span> <span class="p">[</span><span class="n">pop</span> <span class="o">++</span><span class="p">]</span> <span class="n">step</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="mi">0</span> <span class="o">.</span> <span class="n">swap</span> <span class="p">[</span><span class="n">pop</span> <span class="o">++</span><span class="p">]</span> <span class="n">step</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="o">.</span> <span class="p">[</span><span class="n">pop</span> <span class="o">++</span><span class="p">]</span> <span class="n">step</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="o">++</span><span class="p">]</span> <span class="o">.</span> <span class="n">step</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">0</span> <span class="mi">23</span> <span class="p">[</span><span class="n">pop</span> <span class="o">++</span><span class="p">]</span> <span class="o">.</span> <span class="n">i</span> <span class="p">[</span><span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="o">++</span><span class="p">]</span> <span class="n">step</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">0</span> <span class="mi">23</span> <span class="o">.</span> <span class="n">pop</span> <span class="o">++</span> <span class="p">[</span><span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="o">++</span><span class="p">]</span> <span class="n">step</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">0</span> <span class="o">.</span> <span class="o">++</span> <span class="p">[</span><span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="o">++</span><span class="p">]</span> <span class="n">step</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">1</span> <span class="o">.</span> <span class="p">[</span><span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="o">++</span><span class="p">]</span> <span class="n">step</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">1</span> <span class="p">[</span><span class="mi">18</span><span class="p">]</span> <span class="o">.</span> <span class="p">[</span><span class="n">pop</span> <span class="o">++</span><span class="p">]</span> <span class="n">step</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">1</span> <span class="p">[</span><span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="o">++</span><span class="p">]</span> <span class="o">.</span> <span class="n">step</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">1</span> <span class="mi">18</span> <span class="p">[</span><span class="n">pop</span> <span class="o">++</span><span class="p">]</span> <span class="o">.</span> <span class="n">i</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">1</span> <span class="mi">18</span> <span class="o">.</span> <span class="n">pop</span> <span class="o">++</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">1</span> <span class="o">.</span> <span class="o">++</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">2</span> <span class="o">.</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">2</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="o">.</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="mf">41.0</span> <span class="p">[</span><span class="mi">2</span><span class="p">]</span> <span class="o">.</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="mf">41.0</span> <span class="mi">2</span> <span class="o">.</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="mf">41.0</span> <span class="mi">2</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="o">.</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="mf">41.0</span> <span class="o">.</span> <span class="n">popd</span> <span class="mi">2</span> <span class="o">/</span>
|
||||
<span class="mf">41.0</span> <span class="o">.</span> <span class="mi">2</span> <span class="o">/</span>
|
||||
<span class="mf">41.0</span> <span class="mi">2</span> <span class="o">.</span> <span class="o">/</span>
|
||||
<span class="mf">20.5</span> <span class="o">.</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="replacing-size-with-a-python-version">
|
||||
<h2>Replacing <code class="docutils literal notranslate"><span class="pre">size</span></code> with a Python version<a class="headerlink" href="#replacing-size-with-a-python-version" title="Permalink to this headline">¶</a></h2>
|
||||
<p>Both <code class="docutils literal notranslate"><span class="pre">sum</span></code> and <code class="docutils literal notranslate"><span class="pre">size</span></code> each convert a sequence to a single value.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span> <span class="nb">sum</span> <span class="o">==</span> <span class="mi">0</span> <span class="n">swap</span> <span class="p">[</span><span class="o">+</span><span class="p">]</span> <span class="n">step</span>
|
||||
<span class="n">size</span> <span class="o">==</span> <span class="mi">0</span> <span class="n">swap</span> <span class="p">[</span><span class="n">pop</span> <span class="o">++</span><span class="p">]</span> <span class="n">step</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>An efficient <code class="docutils literal notranslate"><span class="pre">sum</span></code> function is already in the library. But for
|
||||
<code class="docutils literal notranslate"><span class="pre">size</span></code> we can use a “compiled” version hand-written in Python to speed
|
||||
up evaluation and make the trace more readable.</p>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">joy.library</span> <span class="k">import</span> <span class="n">SimpleFunctionWrapper</span>
|
||||
<span class="kn">from</span> <span class="nn">joy.utils.stack</span> <span class="k">import</span> <span class="n">iter_stack</span>
|
||||
|
||||
|
||||
<span class="nd">@SimpleFunctionWrapper</span>
|
||||
<span class="k">def</span> <span class="nf">size</span><span class="p">(</span><span class="n">stack</span><span class="p">):</span>
|
||||
<span class="sd">'''Return the size of the sequence on the stack.'''</span>
|
||||
<span class="n">sequence</span><span class="p">,</span> <span class="n">stack</span> <span class="o">=</span> <span class="n">stack</span>
|
||||
<span class="n">n</span> <span class="o">=</span> <span class="mi">0</span>
|
||||
<span class="k">for</span> <span class="n">_</span> <span class="ow">in</span> <span class="n">iter_stack</span><span class="p">(</span><span class="n">sequence</span><span class="p">):</span>
|
||||
<span class="n">n</span> <span class="o">+=</span> <span class="mi">1</span>
|
||||
<span class="k">return</span> <span class="n">n</span><span class="p">,</span> <span class="n">stack</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Now we replace the old version in the dictionary with the new version,
|
||||
and re-evaluate the expression.</p>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">D</span><span class="p">[</span><span class="s1">'size'</span><span class="p">]</span> <span class="o">=</span> <span class="n">size</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="a-shorter-trace">
|
||||
<h2>A shorter trace<a class="headerlink" href="#a-shorter-trace" title="Permalink to this headline">¶</a></h2>
|
||||
<p>You can see that <code class="docutils literal notranslate"><span class="pre">size</span></code> now executes in a single step.</p>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">V</span><span class="p">(</span><span class="s1">'[23 18] average'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span> <span class="o">.</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="n">average</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="o">.</span> <span class="n">average</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="o">.</span> <span class="p">[</span><span class="nb">sum</span> <span class="mf">1.0</span> <span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">size</span><span class="p">]</span> <span class="n">cleave</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="nb">sum</span> <span class="mf">1.0</span> <span class="o">*</span><span class="p">]</span> <span class="o">.</span> <span class="p">[</span><span class="n">size</span><span class="p">]</span> <span class="n">cleave</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="nb">sum</span> <span class="mf">1.0</span> <span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">size</span><span class="p">]</span> <span class="o">.</span> <span class="n">cleave</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="nb">sum</span> <span class="mf">1.0</span> <span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">size</span><span class="p">]</span> <span class="o">.</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">app2</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="nb">sum</span> <span class="mf">1.0</span> <span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">.</span> <span class="n">app2</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[[</span><span class="nb">sum</span> <span class="mf">1.0</span> <span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">.</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="nb">sum</span> <span class="mf">1.0</span> <span class="o">*</span><span class="p">]</span> <span class="o">.</span> <span class="n">i</span> <span class="p">[[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="o">.</span> <span class="nb">sum</span> <span class="mf">1.0</span> <span class="o">*</span> <span class="p">[[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">41</span> <span class="o">.</span> <span class="mf">1.0</span> <span class="o">*</span> <span class="p">[[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">41</span> <span class="mf">1.0</span> <span class="o">.</span> <span class="o">*</span> <span class="p">[[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mf">41.0</span> <span class="o">.</span> <span class="p">[[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mf">41.0</span> <span class="p">[[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="o">.</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="mf">41.0</span><span class="p">]</span> <span class="o">.</span> <span class="n">first</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="mf">41.0</span> <span class="o">.</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="mf">41.0</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="o">.</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="mf">41.0</span> <span class="p">[[</span><span class="n">size</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="o">.</span> <span class="n">infra</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="p">[</span><span class="n">size</span><span class="p">]</span> <span class="o">.</span> <span class="n">i</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="o">.</span> <span class="n">size</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">2</span> <span class="o">.</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="mi">2</span> <span class="p">[</span><span class="mf">41.0</span> <span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]]</span> <span class="o">.</span> <span class="n">swaack</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="mf">41.0</span> <span class="p">[</span><span class="mi">2</span><span class="p">]</span> <span class="o">.</span> <span class="n">first</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="mf">41.0</span> <span class="mi">2</span> <span class="o">.</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="mf">41.0</span> <span class="mi">2</span> <span class="p">[</span><span class="n">popd</span><span class="p">]</span> <span class="o">.</span> <span class="n">dip</span> <span class="o">/</span>
|
||||
<span class="p">[</span><span class="mi">23</span> <span class="mi">18</span><span class="p">]</span> <span class="mf">41.0</span> <span class="o">.</span> <span class="n">popd</span> <span class="mi">2</span> <span class="o">/</span>
|
||||
<span class="mf">41.0</span> <span class="o">.</span> <span class="mi">2</span> <span class="o">/</span>
|
||||
<span class="mf">41.0</span> <span class="mi">2</span> <span class="o">.</span> <span class="o">/</span>
|
||||
<span class="mf">20.5</span> <span class="o">.</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
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|
||||
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|
||||
|
||||
|
||||
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|
||||
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|
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|
||||
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|
||||
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|
||||
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|
||||
<li><a class="reference internal" href="#">Replacing Functions in the Dictionary</a><ul>
|
||||
<li><a class="reference internal" href="#a-long-trace">A long trace</a></li>
|
||||
<li><a class="reference internal" href="#replacing-size-with-a-python-version">Replacing <code class="docutils literal notranslate"><span class="pre">size</span></code> with a Python version</a></li>
|
||||
<li><a class="reference internal" href="#a-shorter-trace">A shorter trace</a></li>
|
||||
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|
||||
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|
||||
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|
||||
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|
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<span xmlns:dct="http://purl.org/dc/terms/" property="dct:title">Thun Documentation</span> by <a xmlns:cc="http://creativecommons.org/ns#" href="https://joypy.osdn.io/" property="cc:attributionName" rel="cc:attributionURL">Simon Forman</a> is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License</a>.<br />Based on a work at <a xmlns:dct="http://purl.org/dc/terms/" href="https://osdn.net/projects/joypy/" rel="dct:source">https://osdn.net/projects/joypy/</a>.
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<div class="section" id="treating-trees-ii-treestep">
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<h1>Treating Trees II: <code class="docutils literal notranslate"><span class="pre">treestep</span></code><a class="headerlink" href="#treating-trees-ii-treestep" title="Permalink to this headline">¶</a></h1>
|
||||
<p>Let’s consider a tree structure, similar to one described <a class="reference external" href="https://www.cs.kent.ac.uk/people/staff/dat/miranda/whyfp90.pdf">“Why
|
||||
functional programming matters” by John
|
||||
Hughes</a>,
|
||||
that consists of a node value followed by zero or more child trees. (The
|
||||
asterisk is meant to indicate the <a class="reference external" href="https://en.wikipedia.org/wiki/Kleene_star">Kleene
|
||||
star</a>.)</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">tree</span> <span class="o">=</span> <span class="p">[]</span> <span class="o">|</span> <span class="p">[</span><span class="n">node</span> <span class="n">tree</span><span class="o">*</span><span class="p">]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>In the spirit of <code class="docutils literal notranslate"><span class="pre">step</span></code> we are going to define a combinator
|
||||
<code class="docutils literal notranslate"><span class="pre">treestep</span></code> which expects a tree and three additional items: a
|
||||
base-case function <code class="docutils literal notranslate"><span class="pre">[B]</span></code>, and two quoted programs <code class="docutils literal notranslate"><span class="pre">[N]</span></code> and <code class="docutils literal notranslate"><span class="pre">[C]</span></code>.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">tree</span> <span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="p">[</span><span class="n">C</span><span class="p">]</span> <span class="n">treestep</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>If the current tree node is empty then just execute <code class="docutils literal notranslate"><span class="pre">B</span></code>:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span> <span class="p">[]</span> <span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="p">[</span><span class="n">C</span><span class="p">]</span> <span class="n">treestep</span>
|
||||
<span class="o">---------------------------</span>
|
||||
<span class="p">[]</span> <span class="n">B</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Otherwise, evaluate <code class="docutils literal notranslate"><span class="pre">N</span></code> on the node value, <code class="docutils literal notranslate"><span class="pre">map</span></code> the whole function
|
||||
(abbreviated here as <code class="docutils literal notranslate"><span class="pre">K</span></code>) over the child trees recursively, and then
|
||||
combine the result with <code class="docutils literal notranslate"><span class="pre">C</span></code>.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span> <span class="p">[</span><span class="n">node</span> <span class="n">tree</span><span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="p">[</span><span class="n">C</span><span class="p">]</span> <span class="n">treestep</span>
|
||||
<span class="o">---------------------------------------</span> <span class="n">w</span><span class="o">/</span> <span class="n">K</span> <span class="o">==</span> <span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="p">[</span><span class="n">C</span><span class="p">]</span> <span class="n">treestep</span>
|
||||
<span class="n">node</span> <span class="n">N</span> <span class="p">[</span><span class="n">tree</span><span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="nb">map</span> <span class="n">C</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>(Later on we’ll experiment with making <code class="docutils literal notranslate"><span class="pre">map</span></code> part of <code class="docutils literal notranslate"><span class="pre">C</span></code> so you can
|
||||
use other combinators.)</p>
|
||||
<div class="section" id="derive-the-recursive-function">
|
||||
<h2>Derive the recursive function.<a class="headerlink" href="#derive-the-recursive-function" title="Permalink to this headline">¶</a></h2>
|
||||
<p>We can begin to derive it by finding the <code class="docutils literal notranslate"><span class="pre">ifte</span></code> stage that <code class="docutils literal notranslate"><span class="pre">genrec</span></code>
|
||||
will produce.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">K</span> <span class="o">==</span> <span class="p">[</span><span class="ow">not</span><span class="p">]</span> <span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">R0</span><span class="p">]</span> <span class="p">[</span><span class="n">R1</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="o">==</span> <span class="p">[</span><span class="ow">not</span><span class="p">]</span> <span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">R0</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="n">R1</span><span class="p">]</span> <span class="n">ifte</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>So we just have to derive <code class="docutils literal notranslate"><span class="pre">J</span></code>:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span> <span class="o">==</span> <span class="n">R0</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="n">R1</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>The behavior of <code class="docutils literal notranslate"><span class="pre">J</span></code> is to accept a (non-empty) tree node and arrive at
|
||||
the desired outcome.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span> <span class="p">[</span><span class="n">node</span> <span class="n">tree</span><span class="o">*</span><span class="p">]</span> <span class="n">J</span>
|
||||
<span class="o">------------------------------</span>
|
||||
<span class="n">node</span> <span class="n">N</span> <span class="p">[</span><span class="n">tree</span><span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="nb">map</span> <span class="n">C</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>So <code class="docutils literal notranslate"><span class="pre">J</span></code> will have some form like:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span> <span class="o">==</span> <span class="o">...</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="o">...</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="o">...</span> <span class="p">[</span><span class="n">C</span><span class="p">]</span> <span class="o">...</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Let’s dive in. First, unquote the node and <code class="docutils literal notranslate"><span class="pre">dip</span></code> <code class="docutils literal notranslate"><span class="pre">N</span></code>.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="n">node</span> <span class="n">tree</span><span class="o">*</span><span class="p">]</span> <span class="n">uncons</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="n">dip</span>
|
||||
<span class="n">node</span> <span class="p">[</span><span class="n">tree</span><span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="n">dip</span>
|
||||
<span class="n">node</span> <span class="n">N</span> <span class="p">[</span><span class="n">tree</span><span class="o">*</span><span class="p">]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Next, <code class="docutils literal notranslate"><span class="pre">map</span></code> <code class="docutils literal notranslate"><span class="pre">K</span></code> over the child trees and combine with <code class="docutils literal notranslate"><span class="pre">C</span></code>.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">node</span> <span class="n">N</span> <span class="p">[</span><span class="n">tree</span><span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="nb">map</span> <span class="n">C</span>
|
||||
<span class="n">node</span> <span class="n">N</span> <span class="p">[</span><span class="n">tree</span><span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="nb">map</span> <span class="n">C</span>
|
||||
<span class="n">node</span> <span class="n">N</span> <span class="p">[</span><span class="n">K</span><span class="o">.</span><span class="n">tree</span><span class="o">*</span><span class="p">]</span> <span class="n">C</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>So:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span> <span class="o">==</span> <span class="n">uncons</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="n">dip</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="nb">map</span> <span class="n">C</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Plug it in and convert to <code class="docutils literal notranslate"><span class="pre">genrec</span></code>:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">K</span> <span class="o">==</span> <span class="p">[</span><span class="ow">not</span><span class="p">]</span> <span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">J</span> <span class="p">]</span> <span class="n">ifte</span>
|
||||
<span class="o">==</span> <span class="p">[</span><span class="ow">not</span><span class="p">]</span> <span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">uncons</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="n">dip</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="nb">map</span> <span class="n">C</span><span class="p">]</span> <span class="n">ifte</span>
|
||||
<span class="o">==</span> <span class="p">[</span><span class="ow">not</span><span class="p">]</span> <span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">uncons</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="n">dip</span><span class="p">]</span> <span class="p">[</span><span class="nb">map</span> <span class="n">C</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="extract-the-givens-to-parameterize-the-program">
|
||||
<h2>Extract the givens to parameterize the program.<a class="headerlink" href="#extract-the-givens-to-parameterize-the-program" title="Permalink to this headline">¶</a></h2>
|
||||
<p>Working backwards:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="ow">not</span><span class="p">]</span> <span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">uncons</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="n">dip</span><span class="p">]</span> <span class="p">[</span><span class="nb">map</span> <span class="n">C</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="ow">not</span><span class="p">]</span> <span class="n">swap</span> <span class="p">[</span><span class="n">uncons</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="n">dip</span><span class="p">]</span> <span class="p">[</span><span class="nb">map</span> <span class="n">C</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">uncons</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="n">dip</span><span class="p">]</span> <span class="p">[[</span><span class="ow">not</span><span class="p">]</span> <span class="n">swap</span><span class="p">]</span> <span class="n">dip</span> <span class="p">[</span><span class="nb">map</span> <span class="n">C</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="o">^^^^^^^^^^^^^^^^</span>
|
||||
<span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[[</span><span class="n">N</span><span class="p">]</span> <span class="n">dip</span><span class="p">]</span> <span class="p">[</span><span class="n">uncons</span><span class="p">]</span> <span class="n">swoncat</span> <span class="p">[[</span><span class="ow">not</span><span class="p">]</span> <span class="n">swap</span><span class="p">]</span> <span class="n">dip</span> <span class="p">[</span><span class="nb">map</span> <span class="n">C</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="p">[</span><span class="n">dip</span><span class="p">]</span> <span class="n">cons</span> <span class="p">[</span><span class="n">uncons</span><span class="p">]</span> <span class="n">swoncat</span> <span class="p">[[</span><span class="ow">not</span><span class="p">]</span> <span class="n">swap</span><span class="p">]</span> <span class="n">dip</span> <span class="p">[</span><span class="nb">map</span> <span class="n">C</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="o">^^^^^^^^^^^^^^^^^^^^^^^^^^^</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Extract a couple of auxiliary definitions:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">TS</span><span class="o">.</span><span class="mi">0</span> <span class="o">==</span> <span class="p">[[</span><span class="ow">not</span><span class="p">]</span> <span class="n">swap</span><span class="p">]</span> <span class="n">dip</span>
|
||||
<span class="n">TS</span><span class="o">.</span><span class="mi">1</span> <span class="o">==</span> <span class="p">[</span><span class="n">dip</span><span class="p">]</span> <span class="n">cons</span> <span class="p">[</span><span class="n">uncons</span><span class="p">]</span> <span class="n">swoncat</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="n">TS</span><span class="o">.</span><span class="mi">1</span> <span class="n">TS</span><span class="o">.</span><span class="mi">0</span> <span class="p">[</span><span class="nb">map</span> <span class="n">C</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="p">[</span><span class="nb">map</span> <span class="n">C</span><span class="p">]</span> <span class="p">[</span><span class="n">TS</span><span class="o">.</span><span class="mi">1</span> <span class="n">TS</span><span class="o">.</span><span class="mi">0</span><span class="p">]</span> <span class="n">dip</span> <span class="n">genrec</span>
|
||||
<span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="p">[</span><span class="n">C</span><span class="p">]</span> <span class="p">[</span><span class="nb">map</span><span class="p">]</span> <span class="n">swoncat</span> <span class="p">[</span><span class="n">TS</span><span class="o">.</span><span class="mi">1</span> <span class="n">TS</span><span class="o">.</span><span class="mi">0</span><span class="p">]</span> <span class="n">dip</span> <span class="n">genrec</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>The givens are all to the left so we have our definition.</p>
|
||||
<div class="section" id="alternate-extract-the-givens-to-parameterize-the-program">
|
||||
<h3>(alternate) Extract the givens to parameterize the program.<a class="headerlink" href="#alternate-extract-the-givens-to-parameterize-the-program" title="Permalink to this headline">¶</a></h3>
|
||||
<p>Working backwards:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="ow">not</span><span class="p">]</span> <span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">uncons</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="n">dip</span><span class="p">]</span> <span class="p">[</span><span class="nb">map</span> <span class="n">C</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="p">[</span><span class="ow">not</span><span class="p">]</span> <span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="p">[</span><span class="n">dip</span><span class="p">]</span> <span class="n">cons</span> <span class="p">[</span><span class="n">uncons</span><span class="p">]</span> <span class="n">swoncat</span> <span class="p">[</span><span class="nb">map</span> <span class="n">C</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="p">[</span><span class="ow">not</span><span class="p">]</span> <span class="n">roll</span><span class="o">></span> <span class="p">[</span><span class="n">dip</span><span class="p">]</span> <span class="n">cons</span> <span class="p">[</span><span class="n">uncons</span><span class="p">]</span> <span class="n">swoncat</span> <span class="p">[</span><span class="nb">map</span> <span class="n">C</span><span class="p">]</span> <span class="n">genrec</span>
|
||||
<span class="o">^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="define-treestep">
|
||||
<h2>Define <code class="docutils literal notranslate"><span class="pre">treestep</span></code><a class="headerlink" href="#define-treestep" title="Permalink to this headline">¶</a></h2>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">notebook_preamble</span> <span class="k">import</span> <span class="n">D</span><span class="p">,</span> <span class="n">J</span><span class="p">,</span> <span class="n">V</span><span class="p">,</span> <span class="n">define</span><span class="p">,</span> <span class="n">DefinitionWrapper</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">DefinitionWrapper</span><span class="o">.</span><span class="n">add_definitions</span><span class="p">(</span><span class="s1">'''</span>
|
||||
|
||||
<span class="s1"> _treestep_0 == [[not] swap] dip</span>
|
||||
<span class="s1"> _treestep_1 == [dip] cons [uncons] swoncat</span>
|
||||
<span class="s1"> treegrind == [_treestep_1 _treestep_0] dip genrec</span>
|
||||
<span class="s1"> treestep == [map] swoncat treegrind</span>
|
||||
|
||||
<span class="s1">'''</span><span class="p">,</span> <span class="n">D</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="examples">
|
||||
<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
|
||||
<p>Consider trees, the nodes of which are integers. We can find the sum of
|
||||
all nodes in a tree with this function:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">sumtree</span> <span class="o">==</span> <span class="p">[</span><span class="n">pop</span> <span class="mi">0</span><span class="p">]</span> <span class="p">[]</span> <span class="p">[</span><span class="nb">sum</span> <span class="o">+</span><span class="p">]</span> <span class="n">treestep</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">define</span><span class="p">(</span><span class="s1">'sumtree == [pop 0] [] [sum +] treestep'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Running this function on an empty tree value gives zero:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span> <span class="p">[]</span> <span class="p">[</span><span class="n">pop</span> <span class="mi">0</span><span class="p">]</span> <span class="p">[]</span> <span class="p">[</span><span class="nb">sum</span> <span class="o">+</span><span class="p">]</span> <span class="n">treestep</span>
|
||||
<span class="o">------------------------------------</span>
|
||||
<span class="mi">0</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[] sumtree'</span><span class="p">)</span> <span class="c1"># Empty tree.</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">0</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Running it on a non-empty node:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="n">n</span> <span class="n">tree</span><span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">pop</span> <span class="mi">0</span><span class="p">]</span> <span class="p">[]</span> <span class="p">[</span><span class="nb">sum</span> <span class="o">+</span><span class="p">]</span> <span class="n">treestep</span>
|
||||
<span class="n">n</span> <span class="p">[</span><span class="n">tree</span><span class="o">*</span><span class="p">]</span> <span class="p">[[</span><span class="n">pop</span> <span class="mi">0</span><span class="p">]</span> <span class="p">[]</span> <span class="p">[</span><span class="nb">sum</span> <span class="o">+</span><span class="p">]</span> <span class="n">treestep</span><span class="p">]</span> <span class="nb">map</span> <span class="nb">sum</span> <span class="o">+</span>
|
||||
<span class="n">n</span> <span class="p">[</span> <span class="o">...</span> <span class="p">]</span> <span class="nb">sum</span> <span class="o">+</span>
|
||||
<span class="n">n</span> <span class="n">m</span> <span class="o">+</span>
|
||||
<span class="n">n</span><span class="o">+</span><span class="n">m</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[23] sumtree'</span><span class="p">)</span> <span class="c1"># No child trees.</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">23</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[23 []] sumtree'</span><span class="p">)</span> <span class="c1"># Child tree, empty.</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">23</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[23 [2 [4]] [3]] sumtree'</span><span class="p">)</span> <span class="c1"># Non-empty child trees.</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">32</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[23 [2 [8] [9]] [3] [4 []]] sumtree'</span><span class="p">)</span> <span class="c1"># Etc...</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">49</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[23 [2 [8] [9]] [3] [4 []]] [pop 0] [] [cons sum] treestep'</span><span class="p">)</span> <span class="c1"># Alternate "spelling".</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">49</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[23 [2 [8] [9]] [3] [4 []]] [] [pop 23] [cons] treestep'</span><span class="p">)</span> <span class="c1"># Replace each node.</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="mi">23</span> <span class="p">[</span><span class="mi">23</span> <span class="p">[</span><span class="mi">23</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span><span class="p">]]</span> <span class="p">[</span><span class="mi">23</span><span class="p">]</span> <span class="p">[</span><span class="mi">23</span> <span class="p">[]]]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[23 [2 [8] [9]] [3] [4 []]] [] [pop 1] [cons] treestep'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="mi">1</span> <span class="p">[</span><span class="mi">1</span> <span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="p">[</span><span class="mi">1</span><span class="p">]]</span> <span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="p">[</span><span class="mi">1</span> <span class="p">[]]]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[23 [2 [8] [9]] [3] [4 []]] [] [pop 1] [cons] treestep sumtree'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">6</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[23 [2 [8] [9]] [3] [4 []]] [pop 0] [pop 1] [sum +] treestep'</span><span class="p">)</span> <span class="c1"># Combine replace and sum into one function.</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">6</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[4 [3 [] [7]]] [pop 0] [pop 1] [sum +] treestep'</span><span class="p">)</span> <span class="c1"># Combine replace and sum into one function.</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">3</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="redefining-the-ordered-binary-tree-in-terms-of-treestep">
|
||||
<h2>Redefining the Ordered Binary Tree in terms of <code class="docutils literal notranslate"><span class="pre">treestep</span></code>.<a class="headerlink" href="#redefining-the-ordered-binary-tree-in-terms-of-treestep" title="Permalink to this headline">¶</a></h2>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">Tree</span> <span class="o">=</span> <span class="p">[]</span> <span class="o">|</span> <span class="p">[[</span><span class="n">key</span> <span class="n">value</span><span class="p">]</span> <span class="n">left</span> <span class="n">right</span><span class="p">]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>What kind of functions can we write for this with our <code class="docutils literal notranslate"><span class="pre">treestep</span></code>?</p>
|
||||
<p>The pattern for processing a non-empty node is:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">node</span> <span class="n">N</span> <span class="p">[</span><span class="n">tree</span><span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="nb">map</span> <span class="n">C</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Plugging in our BTree structure:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="n">key</span> <span class="n">value</span><span class="p">]</span> <span class="n">N</span> <span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="nb">map</span> <span class="n">C</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="section" id="traversal">
|
||||
<h3>Traversal<a class="headerlink" href="#traversal" title="Permalink to this headline">¶</a></h3>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="n">key</span> <span class="n">value</span><span class="p">]</span> <span class="n">first</span> <span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="nb">map</span> <span class="n">i</span>
|
||||
<span class="n">key</span> <span class="p">[</span><span class="n">value</span><span class="p">]</span> <span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="nb">map</span> <span class="n">i</span>
|
||||
<span class="n">key</span> <span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="nb">map</span> <span class="n">i</span>
|
||||
<span class="n">key</span> <span class="p">[</span><span class="n">lkey</span> <span class="n">rkey</span> <span class="p">]</span> <span class="n">i</span>
|
||||
<span class="n">key</span> <span class="n">lkey</span> <span class="n">rkey</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>This doesn’t quite work:</p>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[[3 0] [[2 0] [][]] [[9 0] [[5 0] [[4 0] [][]] [[8 0] [[6 0] [] [[7 0] [][]]][]]][]]] ["B"] [first] [i] treestep'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">3</span> <span class="s1">'B'</span> <span class="s1">'B'</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Doesn’t work because <code class="docutils literal notranslate"><span class="pre">map</span></code> extracts the <code class="docutils literal notranslate"><span class="pre">first</span></code> item of whatever its
|
||||
mapped function produces. We have to return a list, rather than
|
||||
depositing our results directly on the stack.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="n">key</span> <span class="n">value</span><span class="p">]</span> <span class="n">N</span> <span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="nb">map</span> <span class="n">C</span>
|
||||
|
||||
<span class="p">[</span><span class="n">key</span> <span class="n">value</span><span class="p">]</span> <span class="n">first</span> <span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="nb">map</span> <span class="n">flatten</span> <span class="n">cons</span>
|
||||
<span class="n">key</span> <span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="nb">map</span> <span class="n">flatten</span> <span class="n">cons</span>
|
||||
<span class="n">key</span> <span class="p">[[</span><span class="n">lk</span><span class="p">]</span> <span class="p">[</span><span class="n">rk</span><span class="p">]</span> <span class="p">]</span> <span class="n">flatten</span> <span class="n">cons</span>
|
||||
<span class="n">key</span> <span class="p">[</span> <span class="n">lk</span> <span class="n">rk</span> <span class="p">]</span> <span class="n">cons</span>
|
||||
<span class="p">[</span><span class="n">key</span> <span class="n">lk</span> <span class="n">rk</span> <span class="p">]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>So:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[]</span> <span class="p">[</span><span class="n">first</span><span class="p">]</span> <span class="p">[</span><span class="n">flatten</span> <span class="n">cons</span><span class="p">]</span> <span class="n">treestep</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[[3 0] [[2 0] [] []] [[9 0] [[5 0] [[4 0] [] []] [[8 0] [[6 0] [] [[7 0] [] []]] []]] []]] [] [first] [flatten cons] treestep'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="mi">3</span> <span class="mi">2</span> <span class="mi">9</span> <span class="mi">5</span> <span class="mi">4</span> <span class="mi">8</span> <span class="mi">6</span> <span class="mi">7</span><span class="p">]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>There we go.</p>
|
||||
</div>
|
||||
<div class="section" id="in-order-traversal">
|
||||
<h3>In-order traversal<a class="headerlink" href="#in-order-traversal" title="Permalink to this headline">¶</a></h3>
|
||||
<p>From here:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">key</span> <span class="p">[[</span><span class="n">lk</span><span class="p">]</span> <span class="p">[</span><span class="n">rk</span><span class="p">]]</span> <span class="n">C</span>
|
||||
<span class="n">key</span> <span class="p">[[</span><span class="n">lk</span><span class="p">]</span> <span class="p">[</span><span class="n">rk</span><span class="p">]]</span> <span class="n">i</span>
|
||||
<span class="n">key</span> <span class="p">[</span><span class="n">lk</span><span class="p">]</span> <span class="p">[</span><span class="n">rk</span><span class="p">]</span> <span class="n">roll</span><span class="o"><</span>
|
||||
<span class="p">[</span><span class="n">lk</span><span class="p">]</span> <span class="p">[</span><span class="n">rk</span><span class="p">]</span> <span class="n">key</span> <span class="n">swons</span> <span class="n">concat</span>
|
||||
<span class="p">[</span><span class="n">lk</span><span class="p">]</span> <span class="p">[</span><span class="n">key</span> <span class="n">rk</span><span class="p">]</span> <span class="n">concat</span>
|
||||
<span class="p">[</span><span class="n">lk</span> <span class="n">key</span> <span class="n">rk</span><span class="p">]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>So:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[]</span> <span class="p">[</span><span class="n">i</span> <span class="n">roll</span><span class="o"><</span> <span class="n">swons</span> <span class="n">concat</span><span class="p">]</span> <span class="p">[</span><span class="n">first</span><span class="p">]</span> <span class="n">treestep</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[[3 0] [[2 0] [] []] [[9 0] [[5 0] [[4 0] [] []] [[8 0] [[6 0] [] [[7 0] [] []]] []]] []]] [] [uncons pop] [i roll< swons concat] treestep'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="mi">2</span> <span class="mi">3</span> <span class="mi">4</span> <span class="mi">5</span> <span class="mi">6</span> <span class="mi">7</span> <span class="mi">8</span> <span class="mi">9</span><span class="p">]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="with-treegrind">
|
||||
<h2>With <code class="docutils literal notranslate"><span class="pre">treegrind</span></code>?<a class="headerlink" href="#with-treegrind" title="Permalink to this headline">¶</a></h2>
|
||||
<p>The <code class="docutils literal notranslate"><span class="pre">treegrind</span></code> function doesn’t include the <code class="docutils literal notranslate"><span class="pre">map</span></code> combinator, so
|
||||
the <code class="docutils literal notranslate"><span class="pre">[C]</span></code> function must arrange to use some combinator on the quoted
|
||||
recursive copy <code class="docutils literal notranslate"><span class="pre">[K]</span></code>. With this function, the pattern for processing a
|
||||
non-empty node is:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">node</span> <span class="n">N</span> <span class="p">[</span><span class="n">tree</span><span class="o">*</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="n">C</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Plugging in our BTree structure:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="n">key</span> <span class="n">value</span><span class="p">]</span> <span class="n">N</span> <span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="n">C</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[["key" "value"] ["left"] ["right"] ] ["B"] ["N"] ["C"] treegrind'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="s1">'key'</span> <span class="s1">'value'</span><span class="p">]</span> <span class="s1">'N'</span> <span class="p">[[</span><span class="s1">'left'</span><span class="p">]</span> <span class="p">[</span><span class="s1">'right'</span><span class="p">]]</span> <span class="p">[[</span><span class="ow">not</span><span class="p">]</span> <span class="p">[</span><span class="s1">'B'</span><span class="p">]</span> <span class="p">[</span><span class="n">uncons</span> <span class="p">[</span><span class="s1">'N'</span><span class="p">]</span> <span class="n">dip</span><span class="p">]</span> <span class="p">[</span><span class="s1">'C'</span><span class="p">]</span> <span class="n">genrec</span><span class="p">]</span> <span class="s1">'C'</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="treegrind-with-step">
|
||||
<h2><code class="docutils literal notranslate"><span class="pre">treegrind</span></code> with <code class="docutils literal notranslate"><span class="pre">step</span></code><a class="headerlink" href="#treegrind-with-step" title="Permalink to this headline">¶</a></h2>
|
||||
<p>Iteration through the nodes</p>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[[3 0] [[2 0] [] []] [[9 0] [[5 0] [[4 0] [] []] [[8 0] [[6 0] [] [[7 0] [] []]] []]] []]] [pop] ["N"] [step] treegrind'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="mi">3</span> <span class="mi">0</span><span class="p">]</span> <span class="s1">'N'</span> <span class="p">[</span><span class="mi">2</span> <span class="mi">0</span><span class="p">]</span> <span class="s1">'N'</span> <span class="p">[</span><span class="mi">9</span> <span class="mi">0</span><span class="p">]</span> <span class="s1">'N'</span> <span class="p">[</span><span class="mi">5</span> <span class="mi">0</span><span class="p">]</span> <span class="s1">'N'</span> <span class="p">[</span><span class="mi">4</span> <span class="mi">0</span><span class="p">]</span> <span class="s1">'N'</span> <span class="p">[</span><span class="mi">8</span> <span class="mi">0</span><span class="p">]</span> <span class="s1">'N'</span> <span class="p">[</span><span class="mi">6</span> <span class="mi">0</span><span class="p">]</span> <span class="s1">'N'</span> <span class="p">[</span><span class="mi">7</span> <span class="mi">0</span><span class="p">]</span> <span class="s1">'N'</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Sum the nodes’ keys.</p>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'0 [[3 0] [[2 0] [] []] [[9 0] [[5 0] [[4 0] [] []] [[8 0] [[6 0] [] [[7 0] [] []]] []]] []]] [pop] [first +] [step] treegrind'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">44</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Rebuild the tree using <code class="docutils literal notranslate"><span class="pre">map</span></code> (imitating <code class="docutils literal notranslate"><span class="pre">treestep</span></code>.)</p>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'[[3 0] [[2 0] [] []] [[9 0] [[5 0] [[4 0] [] []] [[8 0] [[6 0] [] [[7 0] [] []]] []]] []]] [] [[100 +] infra] [map cons] treegrind'</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[[</span><span class="mi">103</span> <span class="mi">0</span><span class="p">]</span> <span class="p">[[</span><span class="mi">102</span> <span class="mi">0</span><span class="p">]</span> <span class="p">[]</span> <span class="p">[]]</span> <span class="p">[[</span><span class="mi">109</span> <span class="mi">0</span><span class="p">]</span> <span class="p">[[</span><span class="mi">105</span> <span class="mi">0</span><span class="p">]</span> <span class="p">[[</span><span class="mi">104</span> <span class="mi">0</span><span class="p">]</span> <span class="p">[]</span> <span class="p">[]]</span> <span class="p">[[</span><span class="mi">108</span> <span class="mi">0</span><span class="p">]</span> <span class="p">[[</span><span class="mi">106</span> <span class="mi">0</span><span class="p">]</span> <span class="p">[]</span> <span class="p">[[</span><span class="mi">107</span> <span class="mi">0</span><span class="p">]</span> <span class="p">[]</span> <span class="p">[]]]</span> <span class="p">[]]]</span> <span class="p">[]]]</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="do-we-have-the-flexibility-to-reimplement-tree-get">
|
||||
<h2>Do we have the flexibility to reimplement <code class="docutils literal notranslate"><span class="pre">Tree-get</span></code>?<a class="headerlink" href="#do-we-have-the-flexibility-to-reimplement-tree-get" title="Permalink to this headline">¶</a></h2>
|
||||
<p>I think we do:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">N</span><span class="p">]</span> <span class="p">[</span><span class="n">C</span><span class="p">]</span> <span class="n">treegrind</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>We’ll start by saying that the base-case (the key is not in the tree) is
|
||||
user defined, and the per-node function is just the query key literal:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="n">B</span><span class="p">]</span> <span class="p">[</span><span class="n">query_key</span><span class="p">]</span> <span class="p">[</span><span class="n">C</span><span class="p">]</span> <span class="n">treegrind</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>This means we just have to define <code class="docutils literal notranslate"><span class="pre">C</span></code> from:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="n">key</span> <span class="n">value</span><span class="p">]</span> <span class="n">query_key</span> <span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="n">C</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Let’s try <code class="docutils literal notranslate"><span class="pre">cmp</span></code>:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">C</span> <span class="o">==</span> <span class="n">P</span> <span class="p">[</span><span class="n">T</span><span class="o">></span><span class="p">]</span> <span class="p">[</span><span class="n">E</span><span class="p">]</span> <span class="p">[</span><span class="n">T</span><span class="o"><</span><span class="p">]</span> <span class="nb">cmp</span>
|
||||
|
||||
<span class="p">[</span><span class="n">key</span> <span class="n">value</span><span class="p">]</span> <span class="n">query_key</span> <span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="n">P</span> <span class="p">[</span><span class="n">T</span><span class="o">></span><span class="p">]</span> <span class="p">[</span><span class="n">E</span><span class="p">]</span> <span class="p">[</span><span class="n">T</span><span class="o"><</span><span class="p">]</span> <span class="nb">cmp</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="section" id="the-predicate-p">
|
||||
<h3>The predicate <code class="docutils literal notranslate"><span class="pre">P</span></code><a class="headerlink" href="#the-predicate-p" title="Permalink to this headline">¶</a></h3>
|
||||
<p>Seems pretty easy (we must preserve the value in case the keys are
|
||||
equal):</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="n">key</span> <span class="n">value</span><span class="p">]</span> <span class="n">query_key</span> <span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="n">P</span>
|
||||
<span class="p">[</span><span class="n">key</span> <span class="n">value</span><span class="p">]</span> <span class="n">query_key</span> <span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="n">roll</span><span class="o"><</span>
|
||||
<span class="p">[</span><span class="n">key</span> <span class="n">value</span><span class="p">]</span> <span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="n">query_key</span> <span class="p">[</span><span class="n">roll</span><span class="o"><</span> <span class="n">uncons</span> <span class="n">swap</span><span class="p">]</span> <span class="n">dip</span>
|
||||
|
||||
<span class="p">[</span><span class="n">key</span> <span class="n">value</span><span class="p">]</span> <span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="n">roll</span><span class="o"><</span> <span class="n">uncons</span> <span class="n">swap</span> <span class="n">query_key</span>
|
||||
<span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="p">[</span><span class="n">key</span> <span class="n">value</span><span class="p">]</span> <span class="n">uncons</span> <span class="n">swap</span> <span class="n">query_key</span>
|
||||
<span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="n">key</span> <span class="p">[</span><span class="n">value</span><span class="p">]</span> <span class="n">swap</span> <span class="n">query_key</span>
|
||||
<span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="p">[</span><span class="n">value</span><span class="p">]</span> <span class="n">key</span> <span class="n">query_key</span>
|
||||
|
||||
<span class="n">P</span> <span class="o">==</span> <span class="n">roll</span><span class="o"><</span> <span class="p">[</span><span class="n">roll</span><span class="o"><</span> <span class="n">uncons</span> <span class="n">swap</span><span class="p">]</span> <span class="n">dip</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>(Possibly with a swap at the end? Or just swap <code class="docutils literal notranslate"><span class="pre">T<</span></code> and <code class="docutils literal notranslate"><span class="pre">T></span></code>.)</p>
|
||||
<p>So now:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="p">[</span><span class="n">value</span><span class="p">]</span> <span class="n">key</span> <span class="n">query_key</span> <span class="p">[</span><span class="n">T</span><span class="o">></span><span class="p">]</span> <span class="p">[</span><span class="n">E</span><span class="p">]</span> <span class="p">[</span><span class="n">T</span><span class="o"><</span><span class="p">]</span> <span class="nb">cmp</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>Becomes one of these three:</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="p">[</span><span class="n">value</span><span class="p">]</span> <span class="n">T</span><span class="o">></span>
|
||||
<span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="p">[</span><span class="n">value</span><span class="p">]</span> <span class="n">E</span>
|
||||
<span class="p">[</span><span class="n">left</span> <span class="n">right</span><span class="p">]</span> <span class="p">[</span><span class="n">K</span><span class="p">]</span> <span class="p">[</span><span class="n">value</span><span class="p">]</span> <span class="n">T</span><span class="o"><</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="e">
|
||||
<h3><code class="docutils literal notranslate"><span class="pre">E</span></code><a class="headerlink" href="#e" title="Permalink to this headline">¶</a></h3>
|
||||
<p>Easy.</p>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">E</span> <span class="o">==</span> <span class="n">roll</span><span class="o">></span> <span class="n">popop</span> <span class="n">first</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="t-and-t">
|
||||
<h3><code class="docutils literal notranslate"><span class="pre">T<</span></code> and <code class="docutils literal notranslate"><span class="pre">T></span></code><a class="headerlink" href="#t-and-t" title="Permalink to this headline">¶</a></h3>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">T</span><span class="o"><</span> <span class="o">==</span> <span class="n">pop</span> <span class="p">[</span><span class="n">first</span><span class="p">]</span> <span class="n">dip</span> <span class="n">i</span>
|
||||
<span class="n">T</span><span class="o">></span> <span class="o">==</span> <span class="n">pop</span> <span class="p">[</span><span class="n">second</span><span class="p">]</span> <span class="n">dip</span> <span class="n">i</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="section" id="putting-it-together">
|
||||
<h2>Putting it together<a class="headerlink" href="#putting-it-together" title="Permalink to this headline">¶</a></h2>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">T</span><span class="o">></span> <span class="o">==</span> <span class="n">pop</span> <span class="p">[</span><span class="n">first</span><span class="p">]</span> <span class="n">dip</span> <span class="n">i</span>
|
||||
<span class="n">T</span><span class="o"><</span> <span class="o">==</span> <span class="n">pop</span> <span class="p">[</span><span class="n">second</span><span class="p">]</span> <span class="n">dip</span> <span class="n">i</span>
|
||||
<span class="n">E</span> <span class="o">==</span> <span class="n">roll</span><span class="o">></span> <span class="n">popop</span> <span class="n">first</span>
|
||||
<span class="n">P</span> <span class="o">==</span> <span class="n">roll</span><span class="o"><</span> <span class="p">[</span><span class="n">roll</span><span class="o"><</span> <span class="n">uncons</span> <span class="n">swap</span><span class="p">]</span> <span class="n">dip</span>
|
||||
|
||||
<span class="n">Tree</span><span class="o">-</span><span class="n">get</span> <span class="o">==</span> <span class="p">[</span><span class="n">P</span> <span class="p">[</span><span class="n">T</span><span class="o">></span><span class="p">]</span> <span class="p">[</span><span class="n">E</span><span class="p">]</span> <span class="p">[</span><span class="n">T</span><span class="o"><</span><span class="p">]</span> <span class="nb">cmp</span><span class="p">]</span> <span class="n">treegrind</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<p>To me, that seems simpler than the <code class="docutils literal notranslate"><span class="pre">genrec</span></code> version.</p>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">DefinitionWrapper</span><span class="o">.</span><span class="n">add_definitions</span><span class="p">(</span><span class="s1">'''</span>
|
||||
|
||||
<span class="s1"> T> == pop [first] dip i</span>
|
||||
<span class="s1"> T< == pop [second] dip i</span>
|
||||
<span class="s1"> E == roll> popop first</span>
|
||||
<span class="s1"> P == roll< [roll< uncons swap] dip</span>
|
||||
|
||||
<span class="s1"> Tree-get == [P [T>] [E] [T<] cmp] treegrind</span>
|
||||
|
||||
<span class="s1">'''</span><span class="p">,</span> <span class="n">D</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'''</span><span class="se">\</span>
|
||||
|
||||
<span class="s1">[[3 13] [[2 12] [] []] [[9 19] [[5 15] [[4 14] [] []] [[8 18] [[6 16] [] [[7 17] [] []]] []]] []]]</span>
|
||||
|
||||
<span class="s1">[] [5] Tree-get</span>
|
||||
|
||||
<span class="s1">'''</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">15</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="code ipython2 highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">J</span><span class="p">(</span><span class="s1">'''</span><span class="se">\</span>
|
||||
|
||||
<span class="s1">[[3 13] [[2 12] [] []] [[9 19] [[5 15] [[4 14] [] []] [[8 18] [[6 16] [] [[7 17] [] []]] []]] []]]</span>
|
||||
|
||||
<span class="s1">[pop "nope"] [25] Tree-get</span>
|
||||
|
||||
<span class="s1">'''</span><span class="p">)</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="s1">'nope'</span>
|
||||
</pre></div>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
|
||||
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
<div class="sphinxsidebar" role="navigation" aria-label="main navigation">
|
||||
<div class="sphinxsidebarwrapper">
|
||||
<h3><a href="../index.html">Table Of Contents</a></h3>
|
||||
<ul>
|
||||
<li><a class="reference internal" href="#">Treating Trees II: <code class="docutils literal notranslate"><span class="pre">treestep</span></code></a><ul>
|
||||
<li><a class="reference internal" href="#derive-the-recursive-function">Derive the recursive function.</a></li>
|
||||
<li><a class="reference internal" href="#extract-the-givens-to-parameterize-the-program">Extract the givens to parameterize the program.</a><ul>
|
||||
<li><a class="reference internal" href="#alternate-extract-the-givens-to-parameterize-the-program">(alternate) Extract the givens to parameterize the program.</a></li>
|
||||
</ul>
|
||||
</li>
|
||||
<li><a class="reference internal" href="#define-treestep">Define <code class="docutils literal notranslate"><span class="pre">treestep</span></code></a></li>
|
||||
<li><a class="reference internal" href="#examples">Examples</a></li>
|
||||
<li><a class="reference internal" href="#redefining-the-ordered-binary-tree-in-terms-of-treestep">Redefining the Ordered Binary Tree in terms of <code class="docutils literal notranslate"><span class="pre">treestep</span></code>.</a><ul>
|
||||
<li><a class="reference internal" href="#traversal">Traversal</a></li>
|
||||
<li><a class="reference internal" href="#in-order-traversal">In-order traversal</a></li>
|
||||
</ul>
|
||||
</li>
|
||||
<li><a class="reference internal" href="#with-treegrind">With <code class="docutils literal notranslate"><span class="pre">treegrind</span></code>?</a></li>
|
||||
<li><a class="reference internal" href="#treegrind-with-step"><code class="docutils literal notranslate"><span class="pre">treegrind</span></code> with <code class="docutils literal notranslate"><span class="pre">step</span></code></a></li>
|
||||
<li><a class="reference internal" href="#do-we-have-the-flexibility-to-reimplement-tree-get">Do we have the flexibility to reimplement <code class="docutils literal notranslate"><span class="pre">Tree-get</span></code>?</a><ul>
|
||||
<li><a class="reference internal" href="#the-predicate-p">The predicate <code class="docutils literal notranslate"><span class="pre">P</span></code></a></li>
|
||||
<li><a class="reference internal" href="#e"><code class="docutils literal notranslate"><span class="pre">E</span></code></a></li>
|
||||
<li><a class="reference internal" href="#t-and-t"><code class="docutils literal notranslate"><span class="pre">T<</span></code> and <code class="docutils literal notranslate"><span class="pre">T></span></code></a></li>
|
||||
</ul>
|
||||
</li>
|
||||
<li><a class="reference internal" href="#putting-it-together">Putting it together</a></li>
|
||||
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<span xmlns:dct="http://purl.org/dc/terms/" property="dct:title">Thun Documentation</span> by <a xmlns:cc="http://creativecommons.org/ns#" href="https://joypy.osdn.io/" property="cc:attributionName" rel="cc:attributionURL">Simon Forman</a> is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License</a>.<br />Based on a work at <a xmlns:dct="http://purl.org/dc/terms/" href="https://osdn.net/projects/joypy/" rel="dct:source">https://osdn.net/projects/joypy/</a>.
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