Added predicate random_integer and updated clpb

src/prolog/lib/clpb.pl

@@ -31,6 +31,7 @@
 :- use_module(library(atts)).
 :- use_module(library(lists)).
 :- use_module(library(iso_ext)).
+:- use_module(library(random)).
 :- use_module(library(pairs)).
 :- use_module(library(dcgs)).
 :- use_module(library(error), []).

src/prolog/lib/random.pl

@@ -1,8 +1,43 @@
-:- module(random, [maybe/0, set_random/1]).
+:- module(random, [maybe/0, random/1, random_integer/3, set_random/1]).
 
 % succeeds with probability 0.5.
 maybe :- '$maybe'.
 
+% The higher the precision, the slower it gets.
+random_number_precision(64).
+
+random(R) :-
+    var(R),
+    random_number_precision(N),
+    rnd(N, R).
+
+random_integer(Lower, Upper, R) :-
+    var(R),
+    (   (var(Lower) ; var(Upper)) ->
+            throw(error(instantiation_error, random_integer/3))
+    ;   \+ integer(Lower) ->
+            throw(error(domain_error(integer, Lower), random_integer/3))
+    ;   \+ integer(Upper) ->
+            throw(error(domain_error(integer, Upper), random_integer/3))
+    ;   Upper > Lower,
+        random(R0),
+        R is floor((Upper - Lower) * R0 + Lower)
+    ).
+
+rnd(N, R) :-
+    rnd_(N, 0, R).
+
+rnd_(0, R, R) :- !.
+rnd_(N, R0, R) :-
+    maybe,
+    !,
+    N1 is N - 1,
+    rnd_(N1, R0, R).
+rnd_(N, R0, R) :-
+    N1 is N - 1,
+    R1 is R0 + 1.0 / 2.0 ^ N,
+    rnd_(N1, R1, R).
+
 set_random(Seed) :-
     (   nonvar(Seed) ->
         (  Seed = seed(S) ->