a random state.

implementation-dependent.

The current random state, which is used, for example, by the function random when a random state is not explicitly supplied.

(random-state-p *random-state*) 

→

true

In the example below, the series from any given point is random, but if you backtrack to that point, you get the same series.

(defparameter *snapshot* (make-random-state)) 

→

*SNAPSHOT*



(list (loop for i from 1 to 10 collect (random)) 
      (let ((*random-state* *snapshot*)) 
        (loop for i from 1 to 10 collect (random)))
      (loop for i from 1 to 10 collect (random)) 
      (let ((*random-state* *snapshot*)) 
        (loop for i from 1 to 10 collect (random))))

→

((19 16 44 19 96 15 76 96 13 61) 
 (19 16 44 19 96 15 76 96 13 61) 
 (16 67 0 43 70 79 58 5 63 50) 
 (16 67 0 43 70 79 58 5 63 50))

The implementation.

random.

• Function MAKE-RANDOM-STATE
• Function RANDOM
• Type RANDOM-STATE

Binding *random-state* to a different random state object correctly saves and restores the old random state object.