113 lines
3.2 KiB
Prolog
113 lines
3.2 KiB
Prolog
:- module(error, [must_be/2,
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can_be/2,
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instantiation_error/1,
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domain_error/3,
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type_error/3
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]).
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/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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Written September 2018 by Markus Triska (triska@metalevel.at)
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I place this code in the public domain. Use it in any way you want.
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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
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/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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must_be(Type, Term)
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This predicate is intended for type-checks of built-in predicates.
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It asserts that Term is:
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1) instantiated *and*
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2) instantiated to an instance of the given Type.
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It corresponds to usage mode +Term.
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Currently, the following types are supported:
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- integer
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- atom
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- list
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- boolean
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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
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must_be(Type, Term) :-
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must_be_(type, Type),
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must_be_(Type, Term).
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must_be_(Type, _) :-
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var(Type),
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instantiation_error(must_be/2).
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must_be_(var, Term) :-
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( var(Term) -> true
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; throw(error(uninstantiation_error, must_be/2))
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).
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must_be_(integer, Term) :- check_(integer, integer, Term).
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must_be_(atom, Term) :- check_(atom, atom, Term).
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must_be_(list, Term) :- check_(ilist, list, Term).
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must_be_(type, Term) :- check_(type, type, Term).
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must_be_(boolean, Term) :- check_(boolean, boolean, Term).
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check_(Pred, Type, Term) :-
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( var(Term) -> instantiation_error(must_be/2)
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; call(Pred, Term) -> true
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; type_error(Type, Term, must_be/2)
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).
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boolean(B) :- ( B == true ; B == false ).
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ilist(V) :- var(V), instantiation_error(must_be/2).
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ilist([]).
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ilist([_|Ls]) :- ilist(Ls).
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type(type).
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type(integer).
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type(atom).
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type(list).
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type(var).
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type(boolean).
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/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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can_be(Type, Term)
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This predicate is intended for type-checks of built-in predicates.
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It asserts that there is a substitution which, if applied to Term,
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makes it an instance of Type.
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It corresponds to usage mode ?Term.
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It supports the same types as must_be/2.
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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
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can_be(Type, Term) :-
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must_be(type, Type),
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( var(Term) -> true
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; can_(Type, Term) -> true
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; type_error(Type, Term, can_be/2)
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).
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can_(integer, Term) :- integer(Term).
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can_(atom, Term) :- atom(Term).
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can_(list, Term) :- list_or_partial_list(Term).
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can_(boolean, Term) :- boolean(Term).
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list_or_partial_list(Var) :- var(Var).
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list_or_partial_list([]).
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list_or_partial_list([_|Ls]) :-
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list_or_partial_list(Ls).
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/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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Shorthands for throwing ISO errors.
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instantiation_error(Context) :-
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throw(error(instantiation_error, Context)).
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domain_error(Type, Term, Context) :-
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throw(error(domain_error(Type, Term), Context)).
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type_error(Type, Term, Context) :-
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throw(error(type_error(Type, Term), Context)).
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