make-random-state &optional state → new-state

state — a random state, or nil, or t. The default is nil.

new-state — a random state object.

Creates a fresh object of type random-state suitable for use as the value of *random-state*.

If state is a random state object, the new-state is a copy₅ of that object. If state is nil, the new-state is a copy₅ of the current random state. If state is t, the new-state is a fresh random state object that has been randomly initialized by some means.

 (let* ((rs1 (make-random-state nil)) 
        (rs2 (make-random-state t)) 
        (rs3 (make-random-state rs2)) 
        (rs4 nil)) 
   (list (loop for i from 1 to 10 
               collect (random 100) 
               when (= i 5) 
                do (setq rs4 (make-random-state))) 
         (loop for i from 1 to 10 collect (random 100 rs1)) 
         (loop for i from 1 to 10 collect (random 100 rs2)) 
         (loop for i from 1 to 10 collect (random 100 rs3)) 
         (loop for i from 1 to 10 collect (random 100 rs4)))) 
→ ((29 25 72 57 55 68 24 35 54 65) 
    (29 25 72 57 55 68 24 35 54 65) 
    (93 85 53 99 58 62 2 23 23 59) 
    (93 85 53 99 58 62 2 23 23 59) 
    (68 24 35 54 65 54 55 50 59 49))

Should signal an error of type type-error if state is not a random state, or nil, or t.

random, *random-state*

One important use of make-random-state is to allow the same series of pseudo-random numbers to be generated many times within a single program.