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correct can_be/2 for partial lists

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Example:

    ?- can_be(list, [a,b|Ls]).
    %@ true.
This commit is contained in:
Markus Triska
2018-09-28 18:16:10 +02:00
parent 80def45d38
commit 373546e83d
1 changed files with 14 additions and 7 deletions
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21
src/prolog/lib/error.pl
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@@ -1,4 +1,5 @@
:- module(error, [must_be/2, can_be/2]).
:- module(error, [must_be/2,
can_be/2]).
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Written September 2018 by Markus Triska (triska@metalevel.at)
@@ -47,16 +48,13 @@ 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 asserts that there is a substitution which, if applied to Term,
makes it an instance of Type.
It corresponds to usage mode ?Term.
@@ -66,9 +64,18 @@ ilist([_|Ls]) :- ilist(Ls).
can_be(Type, Term) :-
( var(Term) -> true
; must_be(Type, Term)
; can_(Type, Term) -> true
; type_error(Type, Term)
).
can_(integer, Term) :- integer(Term).
can_(atom, Term) :- atom(Term).
can_(list, Term) :- list_or_partial_list(Term).
list_or_partial_list(Var) :- var(Var).
list_or_partial_list([]).
list_or_partial_list([_|Ls]) :-
list_or_partial_list(Ls).
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Shorthands for throwing ISO errors.