begin work on between library

src/prolog/lib/between.pl

@@ -0,0 +1,48 @@
+:- module(between, [between/3, gen_int/1, gen_nat/1, numlist/2, repeat/1]).
+
+%% TODO: numlist/3, numlist/5.
+
+:- use_module(library(lists), [length/2]).
+
+between(Lower, Upper, Lower) :-
+    Lower =< Upper.
+between(Lower1, Upper, X) :-
+    Lower1 < Upper,
+    Lower2 is Lower1 + 1,
+    between(Lower2, Upper, X).
+
+enumerate_nats(I, I).
+enumerate_nats(I0, N) :-
+    I1 is I0 + 1,
+    enumerate_nats(I1, N).
+
+gen_nat(N) :-
+    integer(N), !, N >= 0.
+gen_nat(N) :-
+    var(N), enumerate_nats(0, N).
+
+enumerate_ints(I, I).
+enumerate_ints(I0, N) :-
+    I0 > 0,
+    N is -I0.
+enumerate_ints(I0, N) :-
+    I1 is I0 + 1,
+    enumerate_ints(I1, N).
+
+gen_int(N) :-
+    integer(N), !.
+gen_int(N) :-
+    var(N), enumerate_ints(0, N).
+
+repeat_integer(N) :-
+    N > 0.
+repeat_integer(N0) :-
+    N0 > 0, N1 is N0 - 1, repeat_integer(N1).
+
+repeat(N) :-
+    integer(N), N > 0, repeat_integer(N).
+
+numlist(Upper, List) :-
+    (  integer(Upper) -> findall(X, between(1, Upper, X), List)
+    ;  List = [_|_], length(List, Upper), findall(X, between(1, Upper, X), List)
+    ).