| p:abstract
| - The Joy programming language 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, due less to design than to a sort of parallel evolution and convergence.
Joy is unusual (except for function-level programming languages and some esoteric ones, such as unlambda) in its lack of a lambda operator, and therefore lack of formal parameters. To illustrate this with a common example, here is how the square function might be defined in an imperative programming language (C):
int square(int x) {
return x*x;
}
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 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 * .
To explain: In Joy, everything is a function that takes a stack as an argument and returns a stack as a result. For instance, the number 5 is not, as it might appear to be, 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 product. 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 gives Joy conciseness and power, as illustrated by this definition of quicksort:
DEFINE qsort ==
[small]
[uncons [>] split]
swap] dip cons concat]
binrec .
recursive 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)." (en)
- The Joy programming language 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, due less to design than to a sort of parallel evolution and convergence.
Joy is unusual (except for function-level programming languages and some esoteric ones, such as unlambda) in its lack of a lambda operator, and therefore lack of formal parameters. To illustrate this with a common example, here is how the square function might be defined in an imperative programming language (C):
int square(int x) {
return x*x;
}
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 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 * .
To explain: In Joy, everything is a function that takes a stack as an argument and returns a stack as a result. For instance, the number 5 is not, as it might appear to be, 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 product. 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 gives Joy conciseness and power, as illustrated by this definition of quicksort:
DEFINE qsort ==
[small]
[uncons [>] split]
swap] dip cons concat]
binrec .
recursive 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). (en)
- Manfred von Thun de Latrobe University en Melbourne, Australia ha producido y está refinando un lenguaje de programación funcional llamado Joy basado en la composición de funciones más que en cálculo lambda. Ha resultado tener muchas similaridades con el lenguaje de programación Forth, y esto debido menos al diseño que a una suerte de evolución paralela y convergente." (es)
- Joy ist eine funktionale Programmiersprache, in der konsequent die umgekehrte Polnische Notation verwendet wird. Joy wurde von Manfred von Thun, tätig an der Latrobe University in Melbourne (Australien), entwickelt.
Der Kerngedanke ist die Komposition von Funktionen, wobei eine Reihe von Kombinatoren zur Verfügung steht. In einfachen Fällen sieht JOY-Code wie FORTH aus, die Aussagekraft ist jedoch weitaus mächtiger, da Datenstrukturen (und gleichermaßen Programmstrukturen) beliebiger Komplexität auf dem Stack (Stapel) verarbeitet werden können.
Beispiel: Fakultät (unter Benützung des Kombinators für primitive Rekursion):
[1] [*] primrec
Aufrufbeispiel:
5 [1] [*] primrec
was so zu verstehen ist:
* Lege der Reihe nach die Konstante 5 und die Listen [1] und [*] auf den Stapel.
* primrec liest die obersten drei Stapelelemente. Wenn das dritte gleich 0 ist, wird das zweite [1] als Ergebnis auf den Stapel gelegt. Andernfalls wird es um 1 dekrementiert, auf den Stapel gelegt, und rekursiv wieder primrec aufgerufen. Auf dem Rückweg wird das erste Element [*] als Funktion auf die beiden obersten Stapelelemente angewandt und das Ergebnis (in diesem Fall 120) wieder auf den Stapel gelegt." (de)
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| rdfs:comment
| - The Joy programming language 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, due less to design than to a sort of parallel evolution and convergence. (en)
- Manfred von Thun de Latrobe University en Melbourne, Australia ha producido y está refinando un lenguaje de programación funcional llamado Joy basado en la composición de funciones más que en cálculo lambda. Ha resultado tener muchas similaridades con el lenguaje de programación Forth, y esto debido menos al diseño que a una suerte de evolución paralela y convergente." (es)
- Joy ist eine funktionale Programmiersprache, in der konsequent die umgekehrte Polnische Notation verwendet wird. Joy wurde von Manfred von Thun, tätig an der Latrobe University in Melbourne (Australien), entwickelt. Der Kerngedanke ist die Komposition von Funktionen, wobei eine Reihe von Kombinatoren zur Verfügung steht." (de)
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