View source for Call Queue

'''Call Queue''' is an idea for a [[queue]]-based [[esoteric programming language]], thought of by [[User:Koen]] in 2013. Basically, a program in Call Queue looks like a program in your average imperative programming language, except functions are executed using a "call queue" instead of the usual call stack.

Call Queue was inspired by the similarities between a queue-based algorithm implementing breadth-first search in a tree, and a stack-based algorithm emulating recursion.

==Semantics==
===Syntax===
A program in Call Queue is a set of function declarations. A function declaration consists in the function prototype, which informs its name and its arguments, and the function body, which is a sequence of statements.

A statement is either an atom or a function call. Atoms are built-in minimal functions.

One of the functions must be named <code>main</code>.

===Execution===
When execution starts, the body of the function <code>main</code> is converted into a queue of statements, thereafter referred to as the '''call queue'''.

Execution proceeds in a loop:
* While the call queue isn't empty
** Dequeue the first element from the call queue
*** If it is an atom, execute it.
*** If it is a function call, append its body (as a queue of statements) to the call queue

===Atoms===
''This section is empty. Call Queue is yet unfinished.''

==Example programs==
Since the atoms haven't been defined yet, it is currently impossible to write a real program in Call Queue. The following is a dummy program that illustrates how execution unwraps, assuming the single-letter words in capital are atoms.
 function a() { A; c(); d(); }
 function b() { B; e(); f(); }
 function c() { C; }
 function d() { D; }
 function e() { E; }
 function f() { F; }
 function main() { M; a(); b(); }
The call queue would develop as follows:
 M a() b()
 a() b()
 b() A c() d()
 A c() d() B e() f()
 c() d() B e() f()
 d() B e() f() C
 B e() f() C D
 e() f() C D
 f() C D E
 C D E F
 D E F
 E F
 F
Finally, atoms have been executed in the order <code>M A B C D E F</code>.

This is different from usual programming languages using a call stack, where such a program would end up with atoms being executed in the order <code>M A C D B E F</code>.

===Implementations===

* [[Call Queue/if Call Queue|if Call Queue]] ([https://gist.github.com/Camto/0bf141ca44d373dc632be4daf0b534c5 files])

[[Category:Languages]][[Category:Queue-based]][[Category:Usability unknown]][[Category:Unknown computational class]][[Category:2013]][[Category:Implemented]]