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randomprolograndom-seedyap

YAP Prolog random's lack of randomness

When executing the following Prolog program with YAP, the output is always the same, namely the integer 233.

:- use_module(library(random)).    
x:- random(1,1000,X), writeln(X).

For instance, if I execute the following bash script, the output is always the same integer (233).

for k in `seq 0`
do
  yap -l test.pl << %
  x.
%
done

If I repeat this procedure using swipl, then the output is different each time, i.e random.

Can anyone explain this?

Solution

  • usually, random generators require something like set_seed(SomeReallyRandomValue) call, in C was often used seed(time(0)). So, I guess

    datime(datime(_Year, _Month, _DayOfTheMonth, _Hour, Minute, Second)),
X is Minute * Second,Y=X,Z=X,
setrand(rand(X,Y,Z)),

    could work