correct conformity errors

src/prolog/lib/numbervars.pl

@@ -0,0 +1,33 @@
+:- module(numbervars, [numbervars/2, numbervars/3]).
+
+numbervars(Term, NewTerm) :- duplicate_term(Term, NewTerm), numbervars(Term, NewTerm, 0, _).
+
+numbervars(Term, NewTerm, N) :-
+    ( integer(N), N >= 0 -> duplicate_term(Term, NewTerm), numbervars(Term, NewTerm, N, _)
+    ; integer(N) -> throw(error(domain_error(not_less_than_zero, N), numbervars/3))
+    ; throw(error(type_error(integer, N), numbervars/3))
+    ).
+
+numbervars(Term, NewTerm, N1, N2) :-
+    var(Term), !, NewTerm = '$VAR'(N1), N2 is N1 + 1.
+numbervars([Arg | Args], NewTerms, N1, N2) :- !,
+    fold_numbervars([Arg | Args], NewTerms, N1, N2).
+numbervars(Term, NewTerm, N1, N2) :- compound(Term), !,
+    Term =.. [Name | Args],
+    NewTerm =.. [Name | NewArgs],
+    fold_numbervars(Args, NewArgs, N1, N2).
+numbervars(_, _, _, _).
+
+marked_already(Term, NewTerm) :-
+    var(Term), nonvar(NewTerm), NewTerm = '$VAR'(_).
+marked_already(Term, NewTerm) :-
+    atomic(Term).
+
+fold_numbervars([HeadTerm | Terms], [NewHeadTerm | NewTerms], N1, Nn) :-
+    ( marked_already(HeadTerm, NewHeadTerm) -> N1 = N2
+    ; numbervars(HeadTerm, NewHeadTerm, N1, N2),
+      ( var(N2) -> N1 = N2
+      ; true )
+    ),
+    fold_numbervars(Terms, NewTerms, N2, Nn).
+fold_numbervars([], [], _, _).