add error.pl, correct numbervars/3

src/prolog/lib/error.pl

@@ -0,0 +1,84 @@
+:- module(error, [must_be/2, can_be/2]).
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Written September 2018 by Markus Triska (triska@metalevel.at)
+   I place this code in the public domain. Use it in any way you want.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   must_be(Type, Term)
+
+   This predicate is intended for type-checks of built-in predicates.
+
+   It asserts that Term is:
+
+       1) instantiated *and*
+       2) instantiated to an instance of the given Type.
+
+   It corresponds to usage mode +Term.
+
+   Currently, the following types are supported:
+
+       - integer
+       - atom
+       - list.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+must_be(Type, Term) :-
+        must_be_(Type, Term).
+
+
+must_be_(Type, _) :-
+        var(Type),
+        instantiation_error(Type).
+must_be_(integer, Term) :- check_(integer, integer, Term).
+must_be_(atom, Term)    :- check_(atom, atom, Term).
+must_be_(list, Term)    :- check_(ilist, list, Term).
+
+check_(Pred, Type, Term) :-
+        (   var(Term) -> instantiation_error(Term)
+        ;   call(Pred, Term) -> true
+        ;   type_error(Type, Term)
+        ).
+
+ilist(V) :- var(V), instantiation_error(V).
+ilist([]).
+ilist([_|Ls]) :- ilist(Ls).
+
+
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   can_be(Type, Term)
+
+   This predicate is intended for type-checks of built-in predicates.
+
+   It asserts that:
+
+       1) Term is either a variable or instantiated *and*
+       2) _if_ it is instantiated, then it is an instance of Type.
+
+   It corresponds to usage mode ?Term.
+
+   It supports the same types as must_be/2.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+
+can_be(Type, Term) :-
+        (   var(Term) -> true
+        ;   must_be(Type, Term)
+        ).
+
+
+/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+   Shorthands for throwing ISO errors.
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
+
+instantiation_error(_Term) :-
+    throw(error(instantiation_error, _)).
+
+domain_error(Type, Term) :-
+    throw(error(domain_error(Type, Term), _)).
+
+type_error(Type, Term) :-
+    throw(error(type_error(Type, Term), _)).