Joy (programming language): Difference between revisions

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|dialects =

|influenced_by = [[Scheme (programming language)|Scheme]], [[FP (programming language)|FP]], [[Forth (programming language)|Forth]]

|influenced = [[Factor (programming language)|Factor]], [[Cat (programming language)|Cat]], V, [[Trith (programming language)|Trith]]

}}

The '''Joy programming language''' in [[computer science]] is a [[purely functional programming language]] that was produced by Manfred von Thun of [[La Trobe University]] in [[Melbourne]], [[Australia]]. Joy is based on composition of functions rather than [[lambda calculus]]. It has turned out to have many similarities to [[Forth (programming language)|Forth]], due not to design but to a sort of parallel evolution and convergence. It was also inspired by the [[Function-level programming|function-level programming style]] of [[John Backus]]'s [[FP (programming language)|FP]].<ref>{{cite web|title=A Conversation with Manfred von Thun|author=Manfred von Thun|url=http://www.nsl.com/papers/interview.htm|access-date=May 31, 2013|date=December 12, 2003|quote=" In the early 1980s I came across the famous Backus paper "Can programming be liberated from the von Neumann style," and I was immediately intrigued by the higher level of programming in his FP."}}</ref>

It has turned out to have many similarities to [[Forth (programming language)|Forth]], due not to design but to an independent evolution and convergence.{{Citation needed|date=October 2024}}

== How it worksOverview ==

Functions in Joy lack [[Parameter (computer science)|formal parameters]]. For example, a function that squares a numeric input can be expressed as follows:<ref>{{cite web|title=An informal tutorial on Joy |url=http://www.latrobe.edu.au/phimvt/joy/j01tut.html |url-status=dead |archive-url=https://web.archive.org/web/20111007030359/http://www.latrobe.edu.au/phimvt/joy/j01tut.html |archive-date=October 7, 2011 }}</ref>

Joy is unusual among functional programming languages (except for [[function-level programming]] languages and some esoteric ones, such as [[Unlambda]]) in its lack of a [[lambda calculus|lambda]] operator, and therefore lack of [[Parameter (computer science)|formal parameters]]. To illustrate this with a common example, here is how the square function might be defined in an [[imperative programming language]] ([[C (programming language)|C]]):

<syntaxhighlight lang="C">

int square(int x)

{

return x * x;

}

</syntaxhighlight>

The variable x is a parameter which is replaced by the argument to be squared when the function is called.

In a [[functional programming|functional]] language ([[Scheme (programming language)|Scheme]]), the same function could be defined:

<syntaxhighlight lang="scheme">

(define square

(lambda (x)

(* x x)))

</syntaxhighlight>

This is different in many ways, but it still uses the parameter x in the same way.

In Joy, the square function is defined:

DEFINE square == dup * .

Line 51 ⟶ 31:

* The '''*''' operator pops two numbers off the stack and pushes their product.

So the square function makes a copy of the top element, and then multiplies the two top elements of the stack, leaving the square of the original top element at the top of the stack, with no need for a formal parameter. This makes Joy concise, as illustrated by this definition of [[quicksort]]:<ref>{{cite web|title=Sequence Library |url=http://www.latrobe.edu.au/phimvt/joy/seqlib.joy |url-status=dead |archive-url=https://web.archive.org/web/20111007030359/http://www.latrobe.edu.au/phimvt/joy/seqlib.joy |archive-date=October 7, 2011 }}</ref>

<pre><nowiki>

DEFINE qsort ==

<nowiki>

[small]

DEFINE qsort ==

[small]

[uncons [>] split]

[unconsswapd [>]cons splitconcat]

binrec.

[enconcat]

</nowiki></pre>

binrec.

</nowiki>

</pre>

"binrec" is one of Joy's many [[recursion|recursive]] [[combinator]]s, implementing binary recursion. It expects four quoted programs on top of the stack which represent:

* the termination condition (if a list is "small" (1 or 0 elements) it is already sorted),

* what to do if the termination condition is met (in this case nothing),

* what to do by default (split the list into two halves by comparing each element with the pivot), and finally

* what to do at the end (insert the pivot between the two sorted halves).

== Mathematical purity ==

In Joy, the [[eval|meaning function]] is a [[homomorphism]] from the [[syntactic monoid]] onto the [[semantics|semantic]] [[monoid]]. That is, the syntactic relation of [[concatenation]] of [[symbol]]s maps directly onto the semantic relation of [[Function composition|composition]] of [[function (mathematics)|functions]]. It is a [[homomorphism]] rather than an [[isomorphism]], because it is [[onto]] but not [[bijection|one-to-one]]; that is, no symbol has more than one meaning, but some sequences of symbols have the same meaning (e.g. "dup +" and "2 *").

Joy is a [[concatenative programming language]]: "The concatenation of two programs denotes the composition of the functions denoted by the two programs".<ref>{{cite web|title=Mathematical Foundations of Joy |url=http://www.latrobe.edu.au/phimvt/joy/j02maf.html |url-status=dead |archive-url=https://web.archive.org/web/20111007025556/http://www.latrobe.edu.au/phimvt/joy/j02maf.html |archive-date=October 7, 2011 }}</ref>

Its library routines mirror those of ISO [[C (programming language)|C]], though the current implementation is not easily extensible with functions written in C.

== See also ==

Line 87 ⟶ 54:

==External links==

* [http{{Webarchive|url=https://web.archive.org/web/20120907202347/https://www.latrobe.edu.au/humanities/research/research-projects/past-projectsphimvt/joy-programming-language .html|title=Official Joy Programming Language Website (La Trobe University)]}}

* [http://www.kevinalbrecht.com/code/joy-mirror/index.html Joy homepage mirror]

* [https://github.com/Wodan58/Joy immediatelyJoy executablesource Joycode] (GitHub-ArchivArchive)

* [http://joy-lang.org/ Compiled informative collection on Joy]

* {{cite journal|first=Paul|last=Freneger|authorlink=Paul Freneger|title=The JOY of forth|journal=[[ACM SIGPLAN Notices]]|volume=38|issue=8|date=August 2003|url=http://portal.acm.org/citation.cfm?id=944579.944583 |pages=15–17 |doi=10.1145/944579.944583|url-access=subscription}}

* [https://github.com/Wodan58/Joy immediately executable Joy] (GitHub-Archiv)

* {{cite journal|first=Paul|last=Freneger|authorlink=Paul Freneger|title=The JOY of forth|journal=[[ACM SIGPLAN Notices]]|volume=38|issue=8|date=August 2003|url=http://portal.acm.org/citation.cfm?id=944579.944583}}

* {{cite journal|first1=Manfred|last1=von Thun|authorlink1=Manfred von Tuhn|first2=Reuben|last2=Thomas|authorlink2=Reuben Thomas|title=Joy: Forth's Functional Cousin|journal=Proceedings of the 17th EuroForth Conference|url=http://www.complang.tuwien.ac.at/anton/euroforth/ef01/thomas01a.pdf|date=October 9, 2001}}

* {{Cite web| url = http://www.drdobbs.com/architecture-and-design/228701299 | author = Christopher Diggins | title = What is a Concatenative Language | date = December 31, 2008 | publisher = Dr. Dobbs | volume =33}}

* {{cite journal|first=Stevan|last=Apter|title=Functional Programming in Joy and K|journal=Vector|url=http://www.vector.org.uk/archive/v214/joy214.htm|access-date=2011-02-28|archive-url=https://web.archive.org/web/20080828115345/http://www.vector.org.uk/archive/v214/joy214.htm|archive-date=2008-08-28|url-status=dead}}

* [https://github.com/Fpstefanmetazip/mjoy mjoy, an interpreter in DelphiLazarus for machinedrawings drawingwith turtle graphics] (Subset of Joy)

* [https://concatenative.org/wiki/view/Joy%20of%20Postfix Joy of Postfix Calculator App] (Subset of Joy)

[[Category:Programming languages]]