Joy (programming language)

Programming language

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Joy

Paradigm| multi-paradigm: functional, concatenative, stack-oriented
Designed by| Manfred von Thun
Developer| Manfred von Thun
John Cowan
First appeared| 2001
Stable release|

March 17, 2003 / March 17, 2003

Typing discipline| strong, dynamic
Major implementations
Joy0, Joy1, "Current Joy", "John Cowan's Joy", "JoyJ (Joy in jvmm)"
Influenced by
Scheme, FP, Forth
Influenced
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 style of John Backus's FP.[1] It has turned out to have many similarities to Forth, due not to design but to an independent evolution and convergence.[citation needed]

## Overview

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Functions in Joy lack formal parameters. For example, a function that squares a numeric input can be expressed as follows:[2]

DEFINE square == dup * .

In Joy, everything is a function that takes a stack as an argument and returns a stack as a result. For instance, the numeral '5' does not represent an integer constant, but instead a short program that pushes the number 5 onto the stack.

* The dup operator simply duplicates the top element of the stack by pushing a copy of it.
* 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:[3]

DEFINE qsort ==
[small]

[uncons [>] split]
[swapd cons concat]
binrec.

## Mathematical purity

[edit]

Joy is a concatenative programming language: "The concatenation of two programs denotes the composition of the functions denoted by the two programs".[4]

## See also

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* RPL
* Concatenative programming language

## References

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1. ^ Manfred von Thun (December 12, 2003). "A Conversation with Manfred von Thun". Retrieved May 31, 2013. " 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."
2. ^ "An informal tutorial on Joy". Archived from the original on October 7, 2011.
3. ^ "Sequence Library". Archived from the original on October 7, 2011.
4. ^ "Mathematical Foundations of Joy". Archived from the original on October 7, 2011.

## External links

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* Official Joy Programming Language Website (La Trobe University) at the Wayback Machine (archived 2012-09-07)
* Joy homepage mirror
* Joy source code (GitHub-Archive)
* Freneger, Paul (August 2003). "The JOY of forth". ACM SIGPLAN Notices. 38 (8): 15–17\. doi:10.1145/944579.944583.
* von Thun, Manfred; Thomas, Reuben (October 9, 2001). "Joy: Forth's Functional Cousin" (PDF). Proceedings of the 17th EuroForth Conference.
* Christopher Diggins (December 31, 2008). "What is a Concatenative Language". Dr. Dobbs.
* Apter, Stevan. "Functional Programming in Joy and K". Vector. Archived from the original on 2008-08-28. Retrieved 2011-02-28.
* mjoy, an interpreter in Lazarus for drawings with turtle graphics (Subset of Joy)
* Joy of Postfix Calculator App (Subset of Joy)