Vocabulary
math.combinatorics

Inputs and outputs

n	a non-negative integer
n!	an integer

Word description
Outputs the product of all positive integers less than or equal to n.

Examples

USING: math.combinatorics prettyprint ; 4 factorial .
24

Definition

USING: kernel math math.ranges memoize sequences ;

IN: math.combinatorics

MEMO: factorial ( n -- n! )
dup 1 > [ [1,b] product ] [ drop 1 ] if ;