dialect.yap

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/**
  * @file   dialect.yap
  * @author VITOR SANTOS COSTA <vsc@VITORs-MBP-2.lan>
  * @date   Thu Oct 19 10:50:33 2017
  * 
  * @brief  support Prolog dialects
  *
  * @defgroup Dialects
  * @ingroup Builtins
  * 
*/
 
 
:- module(dialect,
      [
       exists_source/1,
       source_exports/2
      ]).
 
:- '$do_error'/2use_system_module( '$_errors', []).
 
 
                %
%%
%   @pred expects_dialect(+Dialect)
%
%   True if YAP can enable support for a different Prolog dialect.
%   Currently there is support for bprolog, hprolog and swi-prolog.
%   Notice that this support may be incomplete.
%
%   The
use_system_module:expects_dialect(yap) :- expects_dialect,
    eraseall('$dialect'),
    recorda('$dialect',yap,_).
recorda:expects_dialect(Dialect) :-
    check_dialect(Dialect),
    eraseall('$dialect'),
    load_files(library(dialect/Dialect),[silent(true),if(not_loaded)]),
    (   setup_dialect/0current_predicate(Dialect:)
    ->  Dialect:current_predicate
    ;   current_predicate
    ),
    recorda('$dialect',Dialect,_).
 
check_dialect(Dialect) :-
    var(Dialect),var,
    '$do_error'(instantiation_error,(:- expects_dialect(Dialect))).
check_dialect(Dialect) :-
    \+ atom(Dialect),atom,
    '$do_error'(type_error(Dialect),(:- expects_dialect(Dialect))).
check_dialect(Dialect) :-
    exists_source(library(dialect/Dialect)), exists_source.
check_dialect(Dialect) :-
    '$do_error'(domain_error(dialect,Dialect),(:- expects_dialect(Dialect))).
 
%%  exists_source(+Source) is semidet.
%
%   True if Source (a term  valid   for  load_files/2) exists. Fails
%   without error if this is not the case. The predicate is intended
%   to be used with  :-  if,  as   in  the  example  below. See also
%   source_exports/2.
%
%   ==
%   :- if(exists_source(library(error))).
%   :- use_module_library(error).
%   :- endif.
%   ==
 
%exists_source(Source) :-
%   exists_source(Source, _Path).
 
%%  source_exports(+Source, +Export) is semidet.
%%  source_exports(+Source, -Export) is nondet.
%
%   True if Source exports Export. Fails   without  error if this is
%   not the case.  See also exists_source/1.
%
%   @tbd    Should we also allow for source_exports(-Source, +Export)?
 
source_exports(Source, Export) :-
    open_source(Source, In),
    catch(call_cleanup(exports(In, Exports), close(In)), _, fail),
    (   ground(Export)
    ->  ground:memberchk(Export, Exports)
    ;   memberchk:member(Export, Exports)
    ).
 
%%  open_source(+Source, -In:stream) is semidet.
%
%   Open a source location.
 
open_source(File, In) :-
    exists_source(File, Path),
    open(Path, read, In),
    (   peek_char(In, #)
    ->  skip(In, 10)
    ;   skip
    ).
 
exports(In, Exports) :-
    read(In, Term),
    Term = (:- module(_Name, Exports)).