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<div class="section" id="advent-of-code-2017">
<h1>Advent of Code 2017<a class="headerlink" href="#advent-of-code-2017" title="Permalink to this headline"></a></h1>
<div class="section" id="december-5th">
<h2>December 5th<a class="headerlink" href="#december-5th" title="Permalink to this headline"></a></h2>
<p>…a list of the offsets for each jump. Jumps are relative: -1 moves to
the previous instruction, and 2 skips the next one. Start at the first
instruction in the list. The goal is to follow the jumps until one leads
outside the list.</p>
<p>In addition, these instructions are a little strange; after each jump,
the offset of that instruction increases by 1. So, if you come across an
offset of 3, you would move three instructions forward, but change it to
a 4 for the next time it is encountered.</p>
<p>For example, consider the following list of jump offsets:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">0</span>
<span class="mi">3</span>
<span class="mi">0</span>
<span class="mi">1</span>
<span class="o">-</span><span class="mi">3</span>
</pre></div>
</div>
<p>Positive jumps (“forward”) move downward; negative jumps move upward.
For legibility in this example, these offset values will be written all
on one line, with the current instruction marked in parentheses. The
following steps would be taken before an exit is found:</p>
<ul class="simple">
<li><ol class="first arabic" start="0">
<li>3 0 1 -3 - before we have taken any steps.</li>
</ol>
</li>
<li><ol class="first arabic">
<li>3 0 1 -3 - jump with offset 0 (that is, don’t jump at all).
Fortunately, the instruction is then incremented to 1.</li>
</ol>
</li>
<li>2 (3) 0 1 -3 - step forward because of the instruction we just
modified. The first instruction is incremented again, now to 2.</li>
<li>2 4 0 1 (-3) - jump all the way to the end; leave a 4 behind.</li>
<li>2 (4) 0 1 -2 - go back to where we just were; increment -3 to -2.</li>
<li>2 5 0 1 -2 - jump 4 steps forward, escaping the maze.</li>
</ul>
<p>In this example, the exit is reached in 5 steps.</p>
<p>How many steps does it take to reach the exit?</p>
</div>
<div class="section" id="breakdown">
<h2>Breakdown<a class="headerlink" href="#breakdown" title="Permalink to this headline"></a></h2>
<p>For now, I’m going to assume a starting state with the size of the
sequence pre-computed. We need it to define the exit condition and it is
a trivial preamble to generate it. We then need and <code class="docutils literal notranslate"><span class="pre">index</span></code> and a
<code class="docutils literal notranslate"><span class="pre">step-count</span></code>, which are both initially zero. Then we have the sequence
itself, and some recursive function <code class="docutils literal notranslate"><span class="pre">F</span></code> that does the work.</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span> <span class="n">size</span> <span class="n">index</span> <span class="n">step</span><span class="o">-</span><span class="n">count</span> <span class="p">[</span><span class="o">...</span><span class="p">]</span> <span class="n">F</span>
<span class="o">-----------------------------------</span>
<span class="n">step</span><span class="o">-</span><span class="n">count</span>
<span class="n">F</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">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>
</pre></div>
</div>
<p>Later on I was thinking about it and the Forth heuristic came to mind,
to wit: four things on the stack are kind of much. Immediately I
realized that the size properly belongs in the predicate of <code class="docutils literal notranslate"><span class="pre">F</span></code>! D’oh!</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span> <span class="n">index</span> <span class="n">step</span><span class="o">-</span><span class="n">count</span> <span class="p">[</span><span class="o">...</span><span class="p">]</span> <span class="n">F</span>
<span class="o">------------------------------</span>
<span class="n">step</span><span class="o">-</span><span class="n">count</span>
</pre></div>
</div>
<p>So, let’s start by nailing down the predicate:</p>
<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">P</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>
<span class="o">==</span> <span class="p">[</span><span class="n">P</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>
<span class="mi">0</span> <span class="mi">0</span> <span class="p">[</span><span class="mi">0</span> <span class="mi">3</span> <span class="mi">0</span> <span class="mi">1</span> <span class="o">-</span><span class="mi">3</span><span class="p">]</span> <span class="n">popop</span> <span class="mi">5</span> <span class="o">&gt;=</span>
<span class="n">P</span> <span class="o">==</span> <span class="n">popop</span> <span class="mi">5</span> <span class="o">&gt;=</span>
</pre></div>
</div>
<p>Now we need the else-part:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">index</span> <span class="n">step</span><span class="o">-</span><span class="n">count</span> <span class="p">[</span><span class="mi">0</span> <span class="mi">3</span> <span class="mi">0</span> <span class="mi">1</span> <span class="o">-</span><span class="mi">3</span><span class="p">]</span> <span class="n">roll</span><span class="o">&lt;</span> <span class="n">popop</span>
<span class="n">E</span> <span class="o">==</span> <span class="n">roll</span><span class="o">&lt;</span> <span class="n">popop</span>
</pre></div>
</div>
<p>Last but not least, the recursive branch</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">0</span> <span class="mi">0</span> <span class="p">[</span><span class="mi">0</span> <span class="mi">3</span> <span class="mi">0</span> <span class="mi">1</span> <span class="o">-</span><span class="mi">3</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>
</pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">R1</span></code> function has a big job:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">R1</span> <span class="o">==</span> <span class="n">get</span> <span class="n">the</span> <span class="n">value</span> <span class="n">at</span> <span class="n">index</span>
<span class="n">increment</span> <span class="n">the</span> <span class="n">value</span> <span class="n">at</span> <span class="n">the</span> <span class="n">index</span>
<span class="n">add</span> <span class="n">the</span> <span class="n">value</span> <span class="n">gotten</span> <span class="n">to</span> <span class="n">the</span> <span class="n">index</span>
<span class="n">increment</span> <span class="n">the</span> <span class="n">step</span> <span class="n">count</span>
</pre></div>
</div>
<p>The only tricky thing there is incrementing an integer in the sequence.
Joy sequences are not particularly good for random access. We could
encode the list of jump offsets in a big integer and use math to do the
processing for a good speed-up, but it still wouldn’t beat the
performance of e.g. a mutable array. This is just one of those places
where “plain vanilla” Joypy doesn’t shine (in default performance. The
legendary <em>Sufficiently-Smart Compiler</em> would of course rewrite this
function to use an array “under the hood”.)</p>
<p>In the meantime, I’m going to write a primitive function that just does
what we need.</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><span class="p">,</span> <span class="n">define</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">list_to_stack</span>
<span class="nd">@SimpleFunctionWrapper</span>
<span class="k">def</span> <span class="nf">incr_at</span><span class="p">(</span><span class="n">stack</span><span class="p">):</span>
<span class="sd">&#39;&#39;&#39;Given a index and a sequence of integers, increment the integer at the index.</span>
<span class="sd"> E.g.:</span>
<span class="sd"> 3 [0 1 2 3 4 5] incr_at</span>
<span class="sd"> -----------------------------</span>
<span class="sd"> [0 1 2 4 4 5]</span>
<span class="sd"> &#39;&#39;&#39;</span>
<span class="n">sequence</span><span class="p">,</span> <span class="p">(</span><span class="n">i</span><span class="p">,</span> <span class="n">stack</span><span class="p">)</span> <span class="o">=</span> <span class="n">stack</span>
<span class="n">mem</span> <span class="o">=</span> <span class="p">[]</span>
<span class="k">while</span> <span class="n">i</span> <span class="o">&gt;=</span> <span class="mi">0</span><span class="p">:</span>
<span class="n">term</span><span class="p">,</span> <span class="n">sequence</span> <span class="o">=</span> <span class="n">sequence</span>
<span class="n">mem</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">term</span><span class="p">)</span>
<span class="n">i</span> <span class="o">-=</span> <span class="mi">1</span>
<span class="n">mem</span><span class="p">[</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span> <span class="o">+=</span> <span class="mi">1</span>
<span class="k">return</span> <span class="n">list_to_stack</span><span class="p">(</span><span class="n">mem</span><span class="p">,</span> <span class="n">sequence</span><span class="p">),</span> <span class="n">stack</span>
<span class="n">D</span><span class="p">[</span><span class="s1">&#39;incr_at&#39;</span><span class="p">]</span> <span class="o">=</span> <span class="n">incr_at</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">&#39;3 [0 1 2 3 4 5] incr_at&#39;</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">4</span> <span class="mi">4</span> <span class="mi">5</span><span class="p">]</span>
</pre></div>
</div>
<div class="section" id="get-the-value-at-index">
<h3>get the value at index<a class="headerlink" href="#get-the-value-at-index" title="Permalink to this headline"></a></h3>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">3</span> <span class="mi">0</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> <span class="p">[</span><span class="n">roll</span><span class="o">&lt;</span> <span class="n">at</span><span class="p">]</span> <span class="n">nullary</span>
<span class="mi">3</span> <span class="mi">0</span> <span class="p">[</span><span class="mi">0</span> <span class="mi">1</span> <span class="mi">2</span> <span class="n">n</span> <span class="mi">4</span><span class="p">]</span> <span class="n">n</span>
</pre></div>
</div>
</div>
<div class="section" id="increment-the-value-at-the-index">
<h3>increment the value at the index<a class="headerlink" href="#increment-the-value-at-the-index" title="Permalink to this headline"></a></h3>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">3</span> <span class="mi">0</span> <span class="p">[</span><span class="mi">0</span> <span class="mi">1</span> <span class="mi">2</span> <span class="n">n</span> <span class="mi">4</span><span class="p">]</span> <span class="n">n</span> <span class="p">[</span><span class="n">Q</span><span class="p">]</span> <span class="n">dip</span>
<span class="mi">3</span> <span class="mi">0</span> <span class="p">[</span><span class="mi">0</span> <span class="mi">1</span> <span class="mi">2</span> <span class="n">n</span> <span class="mi">4</span><span class="p">]</span> <span class="n">Q</span> <span class="n">n</span>
<span class="mi">3</span> <span class="mi">0</span> <span class="p">[</span><span class="mi">0</span> <span class="mi">1</span> <span class="mi">2</span> <span class="n">n</span> <span class="mi">4</span><span class="p">]</span> <span class="p">[</span><span class="n">popd</span> <span class="n">incr_at</span><span class="p">]</span> <span class="n">unary</span> <span class="n">n</span>
<span class="mi">3</span> <span class="mi">0</span> <span class="p">[</span><span class="mi">0</span> <span class="mi">1</span> <span class="mi">2</span> <span class="n">n</span><span class="o">+</span><span class="mi">1</span> <span class="mi">4</span><span class="p">]</span> <span class="n">n</span>
</pre></div>
</div>
</div>
<div class="section" id="add-the-value-gotten-to-the-index">
<h3>add the value gotten to the index<a class="headerlink" href="#add-the-value-gotten-to-the-index" title="Permalink to this headline"></a></h3>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">3</span> <span class="mi">0</span> <span class="p">[</span><span class="mi">0</span> <span class="mi">1</span> <span class="mi">2</span> <span class="n">n</span><span class="o">+</span><span class="mi">1</span> <span class="mi">4</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">cons</span> <span class="n">dipd</span>
<span class="mi">3</span> <span class="mi">0</span> <span class="p">[</span><span class="mi">0</span> <span class="mi">1</span> <span class="mi">2</span> <span class="n">n</span><span class="o">+</span><span class="mi">1</span> <span class="mi">4</span><span class="p">]</span> <span class="p">[</span><span class="n">n</span> <span class="o">+</span><span class="p">]</span> <span class="n">dipd</span>
<span class="mi">3</span> <span class="n">n</span> <span class="o">+</span> <span class="mi">0</span> <span class="p">[</span><span class="mi">0</span> <span class="mi">1</span> <span class="mi">2</span> <span class="n">n</span><span class="o">+</span><span class="mi">1</span> <span class="mi">4</span><span class="p">]</span>
<span class="mi">3</span><span class="o">+</span><span class="n">n</span> <span class="mi">0</span> <span class="p">[</span><span class="mi">0</span> <span class="mi">1</span> <span class="mi">2</span> <span class="n">n</span><span class="o">+</span><span class="mi">1</span> <span class="mi">4</span><span class="p">]</span>
</pre></div>
</div>
</div>
<div class="section" id="increment-the-step-count">
<h3>increment the step count<a class="headerlink" href="#increment-the-step-count" title="Permalink to this headline"></a></h3>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">3</span><span class="o">+</span><span class="n">n</span> <span class="mi">0</span> <span class="p">[</span><span class="mi">0</span> <span class="mi">1</span> <span class="mi">2</span> <span class="n">n</span><span class="o">+</span><span class="mi">1</span> <span class="mi">4</span><span class="p">]</span> <span class="p">[</span><span class="o">++</span><span class="p">]</span> <span class="n">dip</span>
<span class="mi">3</span><span class="o">+</span><span class="n">n</span> <span class="mi">1</span> <span class="p">[</span><span class="mi">0</span> <span class="mi">1</span> <span class="mi">2</span> <span class="n">n</span><span class="o">+</span><span class="mi">1</span> <span class="mi">4</span><span class="p">]</span>
</pre></div>
</div>
</div>
<div class="section" id="all-together-now">
<h3>All together now…<a class="headerlink" href="#all-together-now" title="Permalink to this headline"></a></h3>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>get_value == [roll&lt; at] nullary
incr_value == [[popd incr_at] unary] dip
add_value == [+] cons dipd
incr_step_count == [++] dip
R1 == get_value incr_value add_value incr_step_count
F == [P] [T] [R1] primrec
F == [popop !size! &gt;=] [roll&lt; pop] [get_value incr_value add_value incr_step_count] primrec
</pre></div>
</div>
<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">DefinitionWrapper</span>
<span class="n">DefinitionWrapper</span><span class="o">.</span><span class="n">add_definitions</span><span class="p">(</span><span class="s1">&#39;&#39;&#39;</span>
<span class="s1"> get_value == [roll&lt; at] nullary</span>
<span class="s1"> incr_value == [[popd incr_at] unary] dip</span>
<span class="s1"> add_value == [+] cons dipd</span>
<span class="s1">incr_step_count == [++] dip</span>
<span class="s1"> AoC2017.5.0 == get_value incr_value add_value incr_step_count</span>
<span class="s1">&#39;&#39;&#39;</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">define</span><span class="p">(</span><span class="s1">&#39;F == [popop 5 &gt;=] [roll&lt; popop] [AoC2017.5.0] primrec&#39;</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">&#39;0 0 [0 3 0 1 -3] F&#39;</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">5</span>
</pre></div>
</div>
</div>
<div class="section" id="preamble-for-setting-up-predicate-index-and-step-count">
<h3>Preamble for setting up predicate, <code class="docutils literal notranslate"><span class="pre">index</span></code>, and <code class="docutils literal notranslate"><span class="pre">step-count</span></code><a class="headerlink" href="#preamble-for-setting-up-predicate-index-and-step-count" title="Permalink to this headline"></a></h3>
<p>We want to go from this to this:</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="n">AoC2017</span><span class="o">.</span><span class="mf">5.</span><span class="n">preamble</span>
<span class="o">------------------------------</span>
<span class="mi">0</span> <span class="mi">0</span> <span class="p">[</span><span class="o">...</span><span class="p">]</span> <span class="p">[</span><span class="n">popop</span> <span class="n">n</span> <span class="o">&gt;=</span><span class="p">]</span>
</pre></div>
</div>
<p>Where <code class="docutils literal notranslate"><span class="pre">n</span></code> is the size of the sequence.</p>
<p>The first part is obviously <code class="docutils literal notranslate"><span class="pre">0</span> <span class="pre">0</span> <span class="pre">roll&lt;</span></code>, then <code class="docutils literal notranslate"><span class="pre">dup</span> <span class="pre">size</span></code>:</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="mi">0</span> <span class="mi">0</span> <span class="n">roll</span><span class="o">&lt;</span> <span class="n">dup</span> <span class="n">size</span>
<span class="mi">0</span> <span class="mi">0</span> <span class="p">[</span><span class="o">...</span><span class="p">]</span> <span class="n">n</span>
</pre></div>
</div>
<p>Then:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">0</span> <span class="mi">0</span> <span class="p">[</span><span class="o">...</span><span class="p">]</span> <span class="n">n</span> <span class="p">[</span><span class="o">&gt;=</span><span class="p">]</span> <span class="n">cons</span> <span class="p">[</span><span class="n">popop</span><span class="p">]</span> <span class="n">swoncat</span>
</pre></div>
</div>
<p>So:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">init</span><span class="o">-</span><span class="n">index</span><span class="o">-</span><span class="ow">and</span><span class="o">-</span><span class="n">step</span><span class="o">-</span><span class="n">count</span> <span class="o">==</span> <span class="mi">0</span> <span class="mi">0</span> <span class="n">roll</span><span class="o">&lt;</span>
<span class="n">prepare</span><span class="o">-</span><span class="n">predicate</span> <span class="o">==</span> <span class="n">dup</span> <span class="n">size</span> <span class="p">[</span><span class="o">&gt;=</span><span class="p">]</span> <span class="n">cons</span> <span class="p">[</span><span class="n">popop</span><span class="p">]</span> <span class="n">swoncat</span>
<span class="n">AoC2017</span><span class="o">.</span><span class="mf">5.</span><span class="n">preamble</span> <span class="o">==</span> <span class="n">init</span><span class="o">-</span><span class="n">index</span><span class="o">-</span><span class="ow">and</span><span class="o">-</span><span class="n">step</span><span class="o">-</span><span class="n">count</span> <span class="n">prepare</span><span class="o">-</span><span class="n">predicate</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">&#39;&#39;&#39;</span>
<span class="s1">init-index-and-step-count == 0 0 roll&lt;</span>
<span class="s1"> prepare-predicate == dup size [&gt;=] cons [popop] swoncat</span>
<span class="s1"> AoC2017.5.preamble == init-index-and-step-count prepare-predicate</span>
<span class="s1"> AoC2017.5 == AoC2017.5.preamble [roll&lt; popop] [AoC2017.5.0] primrec</span>
<span class="s1">&#39;&#39;&#39;</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">&#39;[0 3 0 1 -3] AoC2017.5&#39;</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">5</span>
</pre></div>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span> <span class="n">AoC2017</span><span class="o">.</span><span class="mi">5</span> <span class="o">==</span> <span class="n">AoC2017</span><span class="o">.</span><span class="mf">5.</span><span class="n">preamble</span> <span class="p">[</span><span class="n">roll</span><span class="o">&lt;</span> <span class="n">popop</span><span class="p">]</span> <span class="p">[</span><span class="n">AoC2017</span><span class="o">.</span><span class="mf">5.0</span><span class="p">]</span> <span class="n">primrec</span>
<span class="n">AoC2017</span><span class="o">.</span><span class="mf">5.0</span> <span class="o">==</span> <span class="n">get_value</span> <span class="n">incr_value</span> <span class="n">add_value</span> <span class="n">incr_step_count</span>
<span class="n">AoC2017</span><span class="o">.</span><span class="mf">5.</span><span class="n">preamble</span> <span class="o">==</span> <span class="n">init</span><span class="o">-</span><span class="n">index</span><span class="o">-</span><span class="ow">and</span><span class="o">-</span><span class="n">step</span><span class="o">-</span><span class="n">count</span> <span class="n">prepare</span><span class="o">-</span><span class="n">predicate</span>
<span class="n">get_value</span> <span class="o">==</span> <span class="p">[</span><span class="n">roll</span><span class="o">&lt;</span> <span class="n">at</span><span class="p">]</span> <span class="n">nullary</span>
<span class="n">incr_value</span> <span class="o">==</span> <span class="p">[[</span><span class="n">popd</span> <span class="n">incr_at</span><span class="p">]</span> <span class="n">unary</span><span class="p">]</span> <span class="n">dip</span>
<span class="n">add_value</span> <span class="o">==</span> <span class="p">[</span><span class="o">+</span><span class="p">]</span> <span class="n">cons</span> <span class="n">dipd</span>
<span class="n">incr_step_count</span> <span class="o">==</span> <span class="p">[</span><span class="o">++</span><span class="p">]</span> <span class="n">dip</span>
<span class="n">init</span><span class="o">-</span><span class="n">index</span><span class="o">-</span><span class="ow">and</span><span class="o">-</span><span class="n">step</span><span class="o">-</span><span class="n">count</span> <span class="o">==</span> <span class="mi">0</span> <span class="mi">0</span> <span class="n">roll</span><span class="o">&lt;</span>
<span class="n">prepare</span><span class="o">-</span><span class="n">predicate</span> <span class="o">==</span> <span class="n">dup</span> <span class="n">size</span> <span class="p">[</span><span class="o">&gt;=</span><span class="p">]</span> <span class="n">cons</span> <span class="p">[</span><span class="n">popop</span><span class="p">]</span> <span class="n">swoncat</span>
</pre></div>
</div>
<p>This is by far the largest program I have yet written in Joy. Even with
the <code class="docutils literal notranslate"><span class="pre">incr_at</span></code> function it is still a bear. There may be an arrangement
of the parameters that would permit more elegant definitions, but it
still wouldn’t be as efficient as something written in assembly, C, or
even Python.</p>
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<h3><a href="../index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Advent of Code 2017</a><ul>
<li><a class="reference internal" href="#december-5th">December 5th</a></li>
<li><a class="reference internal" href="#breakdown">Breakdown</a><ul>
<li><a class="reference internal" href="#get-the-value-at-index">get the value at index</a></li>
<li><a class="reference internal" href="#increment-the-value-at-the-index">increment the value at the index</a></li>
<li><a class="reference internal" href="#add-the-value-gotten-to-the-index">add the value gotten to the index</a></li>
<li><a class="reference internal" href="#increment-the-step-count">increment the step count</a></li>
<li><a class="reference internal" href="#all-together-now">All together now…</a></li>
<li><a class="reference internal" href="#preamble-for-setting-up-predicate-index-and-step-count">Preamble for setting up predicate, <code class="docutils literal notranslate"><span class="pre">index</span></code>, and <code class="docutils literal notranslate"><span class="pre">step-count</span></code></a></li>
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