root/trunk/configs/swi_set_logtalk_context.pl

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  Logtalk - Open source object-oriented logic programming language
%  Release 2.33.3
%
%  Copyright (c) 1998-2008 Paulo Moura.        All Rights Reserved.
%  Logtalk is free software.  You can redistribute it and/or modify
%  it under the terms of the "Artistic License 2.0" as published by 
%  The Perl Foundation. Consult the "LICENSE.txt" file for details.
%
%
%  a useful but fragile hack for SWI Prolog 5.6.x that allows setting the 
%  Logtalk top-level context to other object than the pseudo-object "user"
%  
%  this is useful mostly when debugging as all queries will be interpreted 
%  as being made within the current context (thus, plain Prolog calls must 
%  be made using the {}/1 control construct)
%
%  usage is simple: call the predicate set_logtalk_context(Obj) to switch 
%  the context to "Obj"; call set_logtalk_context(user) to return to the 
%  normal Logtak/Prolog top-level
%
%  as of Logtalk version 2.30.1 you may use in alternative the <</2 control
%  construct, which provides a more robust solution for making queries in 
%  the context of objects other than "user"
%
%  last updated: May 18, 2008
% 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

:- system_module.

:- dynamic('$lgt_current_context_'/2).

'$lgt_current_context_'(user, _).


set_logtalk_context(Obj) :-
    var(Obj),
    throw(error(instantiation_error, set_logtalk_context(Obj))).

set_logtalk_context(Obj) :-
    \+ callable(Obj),
    throw(error(type_error(object_identifier, Obj), set_logtalk_context(Obj))).

set_logtalk_context(Obj) :-
    \+ '$lgt_current_object_'(Obj, _, _, _, _, _, _, _),
    throw(error(existence_error(object, Obj), set_logtalk_context(Obj))).

set_logtalk_context(Obj) :-
    catch('$lgt_set_logtalk_context'(Obj), Error, (writeq(Error), nl, fail)).

'$lgt_set_logtalk_context'(user) :-
    !,
    retract('$lgt_current_context_'(_, HookRef)),
    (   nonvar(HookRef) -> 
        erase(HookRef)
    ;   true
    ),
    assertz('$lgt_current_context_'(user, _)),
    '$set_prompt'('?- ').

'$lgt_set_logtalk_context'(Obj) :-
    retract('$lgt_current_context_'(Old, _)),
    (   Old == user ->
        '$lgt_expand_query_hook'(Hook),
        asserta(Hook, HookRef)
    ;   true
    ),
    assertz('$lgt_current_context_'(Obj, HookRef)),
    term_to_atom(Obj, ObjAtom),
    concat_atom(['[', ObjAtom, '] ?- '], Prompt),
    '$set_prompt'(Prompt).

:- user:dynamic(expand_query/4).
:- user:multifile(expand_query/4).

'$lgt_expand_query_hook'((user:expand_query(Query, Expanded, Bindings, Bindings) :-
    '$lgt_current_context_'(Obj, _),
    '$lgt_current_object_'(Obj, Prefix, _, _, _, _, _, _),
    '$lgt_ctx_ctx'(Ctx, _, Obj, Obj, Obj, Prefix, [], _),
    '$lgt_tr_body'(Query, TQuery, DQuery, Ctx),
    (   '$lgt_dbg_debugging_', '$lgt_debugging_'(Obj) ->
        Expanded = catch(DQuery, Error, '$lgt_runtime_error_handler'(Error))
    ;   Expanded = catch(TQuery, Error, '$lgt_runtime_error_handler'(Error))
    ))).