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{{Short description|Programming language}}

The '''Joy programming language''' is a simple [[functional programming language]] that was produced by Manfred von Thun of [[Latrobe 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 less to design than to a sort of parallel evolution and convergence.

{{Original research|date=May 2009}}

{{Infobox programming language

|name = Joy

|logo =

|paradigm = [[multi-paradigm programming language|multi-paradigm]]: [[functional programming|functional]], [[concatenative programming language|concatenative]], [[Stack-oriented programming language|stack-oriented]]

|year = 2001

|designer = Manfred von Thun

|developer = Manfred von Thun<br>John Cowan

|latest release version = March 17, 2003

|latest release date = March 17, 2003

|typing = [[strong typing|strong]], [[dynamic typing|dynamic]]

|implementations = Joy0, Joy1, "Current Joy", "John Cowan's Joy", "JoyJ (Joy in jvmm)"

|dialects =

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

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

Joy is almost unique (except for [[Function-level programming]] languages and some esoteric ones, such as [[unlambda]]) in its lack of a [[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]]):

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}}

== Overview ==

int square(int x) {

return x*x;

}

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>

The variable x is a formal parameter which is replaced by the actual value to be squared when the function is called. Now here's how the same function would be defined in a [[functional programming|functional]] language ([[Scheme programming language|scheme]]):

(define square

(lambda (x)

(* x x)))

This is different in many ways, but it still uses the formal parameter x in the same way. Now here is how the square function would be defined in joy:

DEFINE square == dup * .

That probably requires some explanation. In joyJoy, everything is a function that takes a [[stack (computingdata structure)|stack]] as an argument and returns a stack as a result. For instance, the numbernumeral '5' isdoes not, as it might appear to be,represent an integer constant, but instead a short program that pushes the number 5 onto the stack. The + operator pops two numbers off the stack and pushes their sum. The dup operator simply duplicates the top element of the stack by pushing a copy of it. So this definition of the square function says to make a copy of the top element and then multiply the two top elements, leaving the square of the original top element on top of the stack. There is no need for a formal parameter at all. This design makes joy one of the most powerful and concise languages, as illustrated by this definition of [[quicksort]]:

* The '''dup''' operator simply duplicates the top element of the stack by pushing a copy of it.

<pre>

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

<nowiki>

DEFINE qsort ==

[small]

[]

[uncons [>] split]

[[swap] dip cons concat]

binrec .

</nowiki>

</pre>

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>

"binrec" is one of joy's many [[recursion|recursive]] [[combinator|combinators]], 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).

<pre><nowiki>

DEFINE qsort ==

[small]

[]

[uncons [>] split]

[[swap] dipswapd cons concat]

binrec .

</nowiki></pre>

== Mathematical purity ==

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>

== See also ==

* [[RPL_(programming_language)|RPL]]

One of the most beautiful aspects of joy is this: the [[meaning]] function is a [[homomorphism]] from the [[syntax|syntactic]] [[monoid]] onto the [[semantics|semantic]] [[monoid]]. The syntactic relation of [[concatenation]] of [[symbol|symbols]] maps directly onto the semantic relation of [[Function composition|composition]] of [[function (mathematics)|functions]]. It is a [[homomorphism]] instead of an [[isomorphism]] because it is [[onto]] but not [[one-to-one]], that is, some sequences of symbols have the same meaning (e.g. "dup +" and "2 *") but no symbol has more than one meaning.

* [[Concatenative programming language]]

== References ==

Joy is the purest implementation of the [[lambda calculus]] as a programming language, but it still manages to be practical and potentially useful, unlike the otherwise similar [[unlambda]].

<references/>

== External link links==

*[http {{Webarchive|url=https://web.archive.org/web/20120907202347/https://www.latrobe.edu.au/philosophy/phimvt/joy.html|title=Official Joy homepage]Programming Language Website (La Trobe University)}}

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

* [https://github.com/Wodan58/Joy Joy source code] (GitHub-Archive)

* {{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}}

* {{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/metazip/mjoy mjoy, an interpreter in Lazarus for drawings with turtle graphics] (Subset of Joy)

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

[[Category:Programming languages]]

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[[Category:Stack-oriented programming languages]]

[[Category:Functional languages]]

[[Category:Academic programming languages]]

[[Category:Programming languages created in 2001]]

[[Category:2001 software]]

[[Category:Dynamic programming languages]]

[[Category:Dynamically typed programming languages]]

[[Category:High-level programming languages]]