For example: (require (lib "27.ss" "srfi")) (define (random-test n)   (printf "Random Test~n")   (do ((i 0 (+ i 1)))       ((= i n) (void))     (printf "~a~n" (random-integer 2147483647)))) (random-test 10) Always gives (when run fresh): Random Test 883280686 1747413071 1934990987 1651205883 1149373624 816936085 1019268308 797581408 1245017087 332329087 While, (require (lib "27.ss" "srfi")) (define (random-test n)   (printf "Random Test~n")   (random-source-randomize! default-random-source)   (do ((i 0 (+ i 1)))       ((= i n) (void))     (printf "~a~n" (random-integer 2147483647)))) (random-test 10) gives different numbers, for example: Random Test 1470382645 805875569 1100848099 2135863374 1325475753 1919491546 1897091264 429945001 741596119 1171299075 Doug <div class="gmail_quote">On Jan 2, 2008 10:54 AM, Doug Williams <<a href="mailto:m.douglas.williams@gmail.com">m.douglas.williams@gmail.com </a>> wrote: <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Actually, SRFI 27 specifies repeatable random sources.  You have to call random-source-randomize! to get different ones.  And, there is a random-source-pseudo-randomize! procedure that gives you multiple, independent, repeatable random sources.  There are also routines in the science collection to create vectors of independent random sources. Doug<div><div></div><div class="Wj3C7c"> <div class="gmail_quote">On Jan 2, 2008 10:21 AM, Chongkai Zhu <<a href="mailto:czhu@cs.utah.edu" target="_blank">czhu@cs.utah.edu</a> > wrote: <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> <div>Erich Rast wrote: > Hi, > > Sorry, I know this is a bit off-topic, but perhaps someone here has > already stumbled across the answer. I'm looking for a good PRNG that > is portable, but it needs to be one that allows me to get exactly the > same PRN sequence from the same seed. > > Can I use SRFI-27 for that purpose or does it only specify the > interface to possibly different PRNGs that might produce different > sequences? > </div>SRFI-27 only specifies the interface to possibly different PRNGs that might produce different sequences. But the reference implementation of SRFI 27 is portable and allows you to get exactly the same PRN sequence from the same seed. <div> > How about the built-in generator of MzScheme, might it change in > future or is it part of the specs that it won't change under the hood? > </div> Matthew just changed the built-in generator of MzScheme, as a result of a discussion here a few days ago. The SRFI 27 implementation in SVN (v399) is build on top of the built-in generator, and produces the same sequence as the reference implementation of SRFI 27. > Best, > > Erich > Chongkai <div><div></div><div> _________________________________________________  For list-related administrative tasks:  <a href="http://list.cs.brown.edu/mailman/listinfo/plt-scheme" target="_blank">http://list.cs.brown.edu/mailman/listinfo/plt-scheme</a> </div></div></blockquote></div> </div></div></blockquote></div>