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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 |
| Majorimplementations | |
| Joy0, Joy1, "Current Joy", "John Cowan's Joy", "JoyJ (Joy in jvmm)" | |
| Influenced by | |
| Scheme,FP,Forth | |
| Influenced | |
| Factor, Cat, V, Trith | |
TheJoy programming language incomputer science is apurely functional programming language that was produced by Manfred von Thun ofLa Trobe University inMelbourne,Australia. Joy is based on composition of functions rather thanlambda calculus. It was inspired by thefunction-level programming style ofJohn Backus'sFP.[1]It has turned out to have many similarities toForth, due not to design but to an independent evolution and convergence.[citation needed]
Functions in Joy lackformal 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 astack 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.
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 ofquicksort:[3]
DEFINE qsort == [small] [] [uncons [>] split] [swapd cons concat] binrec.
Joy is aconcatenative programming language: "The concatenation of two programs denotes the composition of the functions denoted by the two programs".[4]
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.