random

ToC

Allegro CL

ANSI Common Lisp

12 Numbers

12.2 Dictionary of Numbers

12.2.41 random

Function

Syntax:

random limit &optional random-state

random-number

Arguments and Values:

limit - a positive integer, or a positive float.

random-state - a random state. The default is the current random state.

random-number - a non-negative number less than limit and of the same type as limit.

Description:

Returns a pseudo-random number that is a non-negative number less than limit and of the same type as limit.

The random-state, which is modified by this function, encodes the internal state maintained by the random number generator.

An approximately uniform choice distribution is used. If limit is an integer, each of the possible results occurs with (approximate) probability 1/limit.

Examples:

 (<= 0 (random 1000) 1000)  true
 (let ((state1 (make-random-state))
       (state2 (make-random-state)))
   (= (random 1000 state1) (random 1000 state2)))  true

Side Effects:

The random-state is modified.

Exceptional Situations:

Should signal an error of type type-error if limit is not a positive integer or a positive real.

See Also:

make-random-state, *random-state*

Notes:

See Common Lisp: The Language for information about generating random numbers.

Allegro CL Implementation Details:

See cl:random and cl:make-random-state for information on the Allegro CL implementation of random. Note the links are to the documentation for the current Allegro CL version. Replace /current/ in the URL with the Allegro CL version number to see similar documentation is earlier releases.