recursion

This article is about the concept of recursion. For the novel, see Recursion (novel). For computer applications, see Recursion (computer science). For other uses, see recursive.Recursion, in mathematics and computer science, is a method of defining functions in which the function being defined is applied within its own definition. The term is also used more generally to describe a process of repeating objects in a self-similar way. For instance, when the surfaces of two mirrors are almost parallel with each other the nested images that occur are a form of recursion.
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n. recursion, programming method in which a routine or function rereads itself several times until a specific condition is met (Computers)

(n.)
The act of recurring; return.
  

<mathematics, programming> When a function (or procedure) calls itself. Such a function is called "recursive". If the call is via one or more other functions then this group of functions are called "mutually recursive".
If a function will always call itself, however it is called, then it will never terminate. Usually however, it first performs some test on its arguments to check for a "base case" - a condition under which it can return a value without calling itself.
The canonical example of a recursive function is factorial:
factorial 0 = 1 factorial n = n * factorial (n-1)
Functional programming languages rely heavily on recursion, using it where a procedural language would use iteration.
See also recursion, recursive definition, tail recursion.
[Jargon File]
(1996-05-11)