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Re: Make a random-state from a non-random source

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Stefan Monnier <monnier@iro.umontreal.ca> writes:

> Reading the CLHS about `make-random-state` I can't see how to create
> a "deterministic" random state.
>
> I want it to be deterministic in the sense that if I re-run my program
> (including after changing it a bit), I'll get the exact same sequence of
> random numbers.
> It's OK if the sequence is different when run on a different Lisp
> implementation, OTOH.
>
> I guess I could print a random state into a file and then read it back in,
> but that depends on internals, so it's doubly messy.
>
>
> === Stefan


(defun gensym (&optional (thing "G"))
  "Creates a new uninterned symbol whose name is a prefix string (defaults
   to \"G\"), followed by a decimal number. Thing, when supplied, will
   alter the prefix if it is a string, or be used for the decimal number
   if it is a number, of this symbol. The default value of the number is
   the current value of *gensym-counter* which is incremented each time
   it is used."
  (multiple-value-bind (prefix int)
      (if (integerp thing)
          (values "G" thing)
          (values thing (let ((old *gensym-counter*))
                          (setq *gensym-counter* (1+ old))
                          old)))
    (make-symbol (%symbol-nameify prefix int))))




this is from sbcl symbol.lisp.

a very poor way of doing this would look like this...


(let ((*gensym-counter* 25))
           (gensym "CNT"))


I do not recommend doing this with gentemp, at least with sbcl.
Hencefold the worst way to make a random symol..!

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Thread

Make a random-state from a non-random source Stefan Monnier <monnier@iro.umontreal.ca> - 2026-05-04 12:46 -0400
  Re: Make a random-state from a non-random source Alan Bawden <alan@csail.mit.edu> - 2026-05-05 00:45 -0400
    Re: Make a random-state from a non-random source Stefan Monnier <monnier@iro.umontreal.ca> - 2026-05-05 16:03 -0400
      Re: Make a random-state from a non-random source Kaz Kylheku <046-301-5902@kylheku.com> - 2026-06-04 23:45 +0000
  Re: Make a random-state from a non-random source tfb <no_email@invalid.invalid> - 2026-05-09 18:20 +0000
    Re: Make a random-state from a non-random source Stefan Monnier <monnier@iro.umontreal.ca> - 2026-05-11 11:23 -0400
  Re: Make a random-state from a non-random source steve g <sgonedes1977@gmail.com> - 2026-06-01 15:10 -0400
    Re: Make a random-state from a non-random source Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-01 23:58 +0000

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