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Thun

"...as simple as possible, but no simpler."

A dialect of Joy.

Version -10.0.0.  (Version -10 in case I want to change the names of some
functions before the first "real" release, and I'm more-or-less using
https://semver.org/ )

This project started life as part of a Python project called at first
Joypy but then later renamed (after someone claimed the name on PyPI
before me) to Thun in honor of Manfred Von Thun who created Joy.  While
creating a type-inference system for it I realized that it would be much
easier and more flexible to do it in Prolog.  In fact, the Prolog code
(using SWI Prolog) is so much more elegant than the Python version that,
combined with the recent deprecation of Python 2, it convinced me to
switch "whole-hog" to Prolog.  (You can find the original project at:
https://joypy.osdn.io/ )

  ___                     _        ___         _     
 | __|_ ____ _ _ __  _ __| |___   / __|___  __| |___ 
 | _|\ \ / _` | '  \| '_ \ / -_) | (__/ _ \/ _` / -_)
 |___/_\_\__,_|_|_|_| .__/_\___|  \___\___/\__,_\___|
                    |_|                              
Here is an example of Joy code:

    [[[abs]ii <=][[<>][pop !-]||]&&][[!-][[++]][[--]]ifte dip][[pop !-][--][++]ifte]ifte

It might seem unreadable but with a little familiarity it becomes just as
legible as any other notation.  Some layout helps:

    [   [[abs] ii <=]
        [
            [<>] [pop !-] ||
        ] &&
    ]
    [[    !-] [[++]] [[--]] ifte dip]
    [[pop !-]  [--]   [++]  ifte    ]
    ifte

This function accepts two integers on the stack and increments or
decrements one of them such that the new pair of numbers is the next
coordinate pair in a square spiral (like the kind used to construct an
Ulam Spiral).  For more information see docs\notes\on-square-spiral.md

  ___             _   _               _ _ _
 | __|  _ _ _  __| |_(_)___ _ _  __ _| (_) |_ _  _ 
 | _| || | ' \/ _|  _| / _ \ ' \/ _` | | |  _| || |
 |_| \_,_|_||_\__|\__|_\___/_||_\__,_|_|_|\__|\_, |
  __ _ _ _  __| | | _ \_  _ _ _ _ __  ___ ___ |__/ 
 / _` | ' \/ _` | |  _/ || | '_| '_ \/ _ (_-</ -_) 
 \__,_|_||_\__,_| |_|  \_,_|_| | .__/\___/__/\___| 
                               |_|
Functionality and Purpose

It all started about a quarter of a century ago when I first went to
Seattle and found the book in their main branch library: "System Design
from Provably-Correct Constructs".  It presents a version of Dr. Margaret
Hamilton's "Higher Order Software".  Thun is an attempt at making a
system like that.

There are two aspects to this project.  One is the language Joy and tools
to work with it, the other is a kind of user interface that presents Joy
in a way that (hopefully) is much better than current UIs.  Both of these
come together to create what I hope is a fundamentally better computer
system.

At the moment, this repo just contains the Prolog version of Joy.  I'll
bring over the GUI code from the original project or create some new
version, possibly web-based.

Joy

Joy is a notation for programming created by Manfred von Thun that's easy
to use and understand and has many other nice properties.  This Prolog
code implements an interpreter and other tools for a dialect of Joy that
attempts to stay very close to the spirit of Joy but does not precisely
match the behaviour of the original version(s) written in C.  The main
difference between Thun and the originals, other than being written in
Prolog, is that it works by the "Continuation-Passing Style".

The best source (no pun intended) for learning about Joy is the
information made available at the website of La Trobe University (see
below for the URL) which contains source code for the original C
interpreter, Joy language source code for various functions, and a great
deal of fascinating material mostly written by Von Thun on Joy and its
deeper facets as well as how to program in it and several interesting
aspects.  It's quite a treasure trove.

Wikipedia entry for Joy:
https://en.wikipedia.org/wiki/Joy_%28programming_language%29

Homepage at La Trobe University:
http://www.latrobe.edu.au/humanities/research/research-projects/past-projects/joy-programming-language

Joy is stack-based, concatenative, and purely functional.  Currently only
four kinds of fundamental values are recognized: integers, Boolean values
'true' and 'false', symbols (representing the names of functors), and
sequences (enclosed in square brackets.)

    23 dup [21 18 /] [1 [2 [3]]] true false

A Joy expression is just a sequence of items.  Sequences are also called
lists, and sequences intended as programs are called "quoted programs".
Evaluation proceeds by iterating through the terms in the expression,
putting all literals onto the main stack and evaluating functions as they
are encountered.  Functions receive the current stack and return the next
stack.

Functions called "combinators" accept quoted programs on the stack and
run them in various ways.  These combinators factor specific patterns
that provide the effect of control-flow in other languages (such as ifte
which is like if..then..else..)  Combinators receive the current
expession in addition to the stack and return the next expression.  They
work by changing the pending expression the interpreter is about to
execute.

  ___         _        _ _      _   _          
 |_ _|_ _  __| |_ __ _| | |__ _| |_(_)___ _ _  
  | || ' \(_-<  _/ _` | | / _` |  _| / _ \ ' \ 
 |___|_||_/__/\__\__,_|_|_\__,_|\__|_\___/_||_|

Installation

Download or clone the repository, no special installation is required,
although you will need a recent version of SWI Prolog.  No configuration
is required.

  ___                _           
 | _ \_  _ _ _  _ _ (_)_ _  __ _ 
 |   / || | ' \| ' \| | ' \/ _` |
 |_|_\\_,_|_||_|_||_|_|_||_\__, |
                           |___/ 
Running

I just change into the source directory and load the thun.pl into SWI
Prolog.

    PS C:\Users\sforman\Desktop\src\PROLOG\Thun> cd source

    PS C:\Users\sforman\Desktop\src\PROLOG\Thun\source> swipl thun.pl

    Welcome to SWI-Prolog (threaded, 64 bits, version 8.1.4-33-gf5970a6e0)
    SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software.
    Please run ?- license. for legal details.

    For online help and background, visit http://www.swi-prolog.org
    For built-in help, use ?- help(Topic). or ?- apropos(Word).

    1 ?-

Creating a better user interface is a big part of the "meta-project"
here, if you will.  Thun/Joy is the language, the UI is the real project.
I'm thinking a server with multiple clients (web, native) just because
Prolog isn't fabulous at the nitty-gritty of UIs.  There are other logic
languages that have e.g. reactive rules.  Kowalski has a great thing: LPS
(Logic Production Systems) http://lps.doc.ic.ac.uk/

Anyhooo, for now there's not even a REPL.  Use Prolog's.

TODO: Explain the top-level predicates, with examples, this can be put in
the docs directory...

  ___              _
 |   \ _____ _____| |___ _ __  ___ _ _
 | |) / -_) V / -_) / _ \ '_ \/ -_) '_|
 |___/\___|\_/\___|_\___/ .__/\___|_|      _   _
 |   \ ___  __ _  _ _ __|_|__ _ _| |_ __ _| |_(_)___ _ _  
 | |) / _ \/ _| || | '  \/ -_) ' \  _/ _` |  _| / _ \ ' \ 
 |___/\___/\__|\_,_|_|_|_\___|_||_\__\__,_|\__|_\___/_||_|

Developer Documentation

Since there aren't yet any user-facing clients this is pretty much all
developer documentation.  Until the UI side of the project is re-worked
this will mostly be of interest to people who are into formal semanics of
programming languages.

If you already know Prolog then the code should be pretty simple and
straightforward.  The partial reducer is documented in "The Art of
Prolog" so I won't repeat that here.  Other than that there just really
isn't anything to crunchy in there.  The signal virtual of Joy is it's
simplicity after all.

Adding syntax should be avoided.  At some point I'll likely add more
types, and maybe subtype relations between them.  Maybe add the ability
to "tag" types from Joy itself (i.e. the ordered binary tree functions.)

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  / __|___ _ _| |_ _ _(_) |__ _  _| |_(_)___ _ _  ___
 | (__/ _ \ ' \  _| '_| | '_ \ || |  _| / _ \ ' \(_-<
  \___\___/_||_\__|_| |_|_.__/\_,_|\__|_\___/_||_/__/

Contributions

Well, aren't you sweet!  GPL, docs please, "Be excellent to each other."

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 | _ )_  _(_) |__| | / __| |_ __ _| |_ _  _ ___
 | _ \ || | | / _` | \__ \  _/ _` |  _| || (_-<
 |___/\_,_|_|_\__,_| |___/\__\__,_|\__|\_,_/__/

Build Status

No build, no status.