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yap-6.3/pl/modules.yap
vsc 21a3377248 debugger fixes
initial support for JPL
bad calls to garbage collector and gc
debugger fixes


git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@1096 b08c6af1-5177-4d33-ba66-4b1c6b8b522a
2004-07-22 21:32:23 +00:00

652 lines
19 KiB
Prolog

/*************************************************************************
* *
* YAP Prolog *
* *
* Yap Prolog was developed at NCCUP - Universidade do Porto *
* *
* Copyright L.Damas, V.S.Costa and Universidade do Porto 1985-1997 *
* *
**************************************************************************
* *
* File: modules.pl *
* Last rev: *
* mods: *
* comments: module support *
* *
*************************************************************************/
% module handling
use_module(M) :-
'$use_module'(M).
'$use_module'(V) :- var(V), !,
'$do_error'(instantiation_error,use_module(V)).
'$use_module'([]) :- !.
'$use_module'([A|B]) :- !,
'$use_module'(A),
'$use_module'(B).
'$use_module'(M:F) :- atom(M), !,
'$current_module'(M0),
'$change_module'(M),
'$use_module'(F),
'$change_module'(M0).
'$use_module'(File) :-
'$find_in_path'(File,X,use_module(File)), !,
( recorded('$module','$module'(_,X,Publics),_) ->
'$use_module'(File,Publics)
;
'$ensure_loaded'(File)
).
'$use_module'(File) :-
'$do_error'(permission_error(input,stream,File),use_module(File)).
use_module(File,I) :-
'$use_module'(File, I).
'$use_module'(File,Imports) :- var(File), !,
'$do_error'(instantiation_error,use_module(File,Imports)).
'$use_module'(File,Imports) :- var(Imports), !,
'$do_error'(instantiation_error,use_module(File,Imports)).
'$use_module'(M:F, Imports) :- atom(M), !,
'$current_module'(M0),
'$change_module'(M),
'$use_module'(F, Imports),
'$change_module'(M0).
'$use_module'(File,Imports) :-
'$current_module'(M),
'$find_in_path'(File,X,use_module(File,Imports)), !,
'$open'(X,'$csult',Stream,0), !,
( '$loaded'(Stream,M,TrueFileName) -> true
;
% the following avoids import of all public predicates
'$consulting_file_name'(Stream,TrueFileName),
recorda('$importing','$importing'(TrueFileName),R),
'$reconsult'(File,M,Stream)
),
'$close'(Stream),
( var(R) -> true; erased(R) -> true; erase(R)),
( recorded('$module','$module'(TrueFileName,Mod,Publics),_) ->
'$use_preds'(Imports,Publics,Mod,M)
;
true
).
'$use_module'(File,Imports) :-
'$do_error'(permission_error(input,stream,File),use_module(File,Imports)).
use_module(Mod,F,I) :-
'$use_module'(Mod,F,I).
'$use_module'(Module,V,Imports) :- var(V), !,
'$use_module'(Module,Module,Imports).
'$use_module'(Module,M:File,Imports) :-
atom(M), !,
'$current_module'(M0),
'$change_module'(M),
'$use_module'(Module,File,Imports),
'$change_module'(M0).
'$use_module'(Module,File,Imports) :-
'$find_in_path'(File,X,use_module(Module,File,Imports)),
'$open'(X,'$csult',Stream,0), !,
'$current_module'(M),
'$file_name'(Stream,FName),
(
'$loaded'(Stream, M, TrueFileName)
->
true
;
'$consulting_file_name'(Stream,TrueFileName),
% the following avoids import of all public predicates
recorda('$importing','$importing'(TrueFileName),R),
'$reconsult'(File,M,Stream)
),
'$close'(Stream),
( var(R) -> true; erased(R) -> true; erase(R)),
(
recorded('$module','$module'(TrueFileName,Module,Publics),_)
->
'$use_preds'(Imports,Publics,Module,M)
;
true
).
'$use_module'(Module,File,Imports) :-
'$do_error'(permission_error(input,stream,File),use_module(Module,File,Imports)).
'$consulting_file_name'(Stream,F) :-
'$file_name'(Stream, F).
'$module'(_,N,P) :-
'$module_dec'(N,P).
'$module'(O,N,P,Opts) :- !,
'$module'(O,N,P),
'$process_module_decls_options'(Opts,module(Opts,N,P)).
'$process_module_decls_options'(Var,Mod) :-
var(Var),
'$do_error'(instantiation_error,Mod).
'$process_module_decls_options'([],_).
'$process_module_decls_options'([H|L],M) :-
'$process_module_decls_option'(H,M),
'$process_module_decls_options'(L,M).
'$process_module_decls_options'(T,M) :-
'$do_error'(type_error(list,T),M).
'$process_module_decls_option'(Var,M) :-
var(Var),
'$do_error'(instantiation_error,M).
'$process_module_decls_option'(At,_) :-
atom(At),
'$use_module'(At).
'$process_module_decls_option'(library(L),_) :-
'$use_module'(library(L)).
'$process_module_decls_option'(hidden(Bool),M) :-
'$process_hidden_module'(Bool, M).
'$process_module_decls_option'(Opt,M) :-
'$do_error'(domain_error(module_decl_options,Opt),M).
'$process_hidden_module'(TNew,M) :-
'$convert_true_off_mod3'(TNew, New, M),
source_mode(Old, New),
'$prepare_restore_hidden'(Old,New).
'$convert_true_off_mod3'(true, off, _).
'$convert_true_off_mod3'(false, on, _).
'$convert_true_off_mod3'(X, _, M) :-
'$do_error'(domain_error(module_decl_options,hidden(X)),M).
'$prepare_restore_hidden'(Old,Old) :- !.
'$prepare_restore_hidden'(Old,New) :-
recorda('$system_initialisation', source_mode(New,Old), _).
module(N) :-
var(N),
'$do_error'(instantiation_error,module(N)).
module(N) :-
atom(N), !,
% set it as current module.
'$current_module'(_,N).
module(N) :-
'$do_error'(type_error(atom,N),module(N)).
'$module_dec'(N,P) :-
'$current_module'(Old,N),
get_value('$consulting_file',F),
'$add_module_on_file'(N, F, P),
( recorded('$importing','$importing'(F),_) ->
true
;
'$import'(P,N,Old)
).
'$add_module_on_file'(Mod, F, Exports) :-
recorded('$module','$module'(F0,Mod,_),R), !,
'$add_preexisting_module_on_file'(F, F0, Mod, Exports, R).
'$add_module_on_file'(Mod, F, Exports) :-
recorda('$module','$module'(F,Mod,Exports),_).
% redefining a previously-defined file, no problem.
'$add_preexisting_module_on_file'(F, F, Mod, Exports, R) :- !,
erase(R),
( recorded('$import','$import'(M,T,_,_),R), erase(R), fail; true),
recorda('$module','$module'(F,Mod,Exports),_).
'$add_preexisting_module_on_file'(F,F0,Mod,Exports,R) :-
repeat,
format(user_error, "The module ~a is being redefined.~n Old file: ~a~n New file: ~a~nDo you really want to redefine it? (y or n)",[Mod,F0,F]),
'$mod_scan'(C), !,
( C is "y" ->
'$add_preexisting_module_on_file'(F, F, Mod, Exports, R)
;
'$do_error'(permission_error(module,redefined,Mod),module(Mod,Exports))
).
'$mod_scan'(C) :-
get0(C),
'$skipeol'(C),
(C is "y" ; C is "n").
'$import'([],_,_) :- !.
'$import'([N/K|L],M,T) :-
integer(K), atom(N), !,
( '$check_import'(M,T,N,K) ->
( T = user ->
( recordzifnot('$import','$import'(M,user,N,K),_) -> true ; true)
;
( recordaifnot('$import','$import'(M,T,N,K),_) -> true ; true )
)
;
true
),
'$import'(L,M,T).
'$import'([PS|L],M,T) :-
'$do_error'(domain_error(predicate_spec,PS),import([PS|L])).
'$check_import'(M,T,N,K) :-
recorded('$import','$import'(M1,T,N,K),R), M1 \= M, /* ZP */ !,
format(user_error,"NAME CLASH: ~w was already imported to module ~w;~n",[M1:N/K,T]),
format(user_error," Do you want to import it from ~w ? [y or n] ",M),
repeat,
get0(C), '$skipeol'(C),
( C is "y" -> erase(R), !;
C is "n" -> !, fail;
write(user_error, ' Please answer with ''y'' or ''n'' '), fail
).
'$check_import'(_,_,_,_).
% $use_preds(Imports,Publics,Mod,M)
'$use_preds'(M:L,Publics,Mod,_) :-
'$use_preds'(L,Publics,Mod,M).
'$use_preds'([],_,_,_) :- !.
'$use_preds'([P|Ps],Publics,Mod,M) :- !,
'$use_preds'(P,Publics,Mod,M),
'$use_preds'(Ps,Publics,Mod,M).
'$use_preds'(N/K,Publics,M,Mod) :-
( '$member'(N/K,Publics) -> true ;
print_message(warning,import(N/K,Mod,M,private))
),
( '$check_import'(M,Mod,N,K) ->
% format(user_error,'[ Importing ~w to ~w]~n',[M:N/K,Mod]),
% '$trace_module'(importing(M:N/K,Mod)),
(Mod = user ->
( recordzifnot('$import','$import'(M,user,N,K),_) -> true ; true )
;
( recordaifnot('$import','$import'(M,Mod,N,K),_) -> true ; true )
)
;
true
).
% expand module names in a clause
'$module_expansion'(((Mod:H) :-B ),((Mod:H) :- B1),((Mod:H) :- BO),M) :- !,
'$prepare_body_with_correct_modules'(B, M, B0),
'$module_u_vars'(H,UVars,M), % collect head variables in
% expanded positions
'$module_expansion'(B0,B1,BO,M,M,M,UVars). % expand body
'$module_expansion'((H:-B),(H:-B1),(H:-BO),M) :-
'$module_u_vars'(H,UVars,M), % collect head variables in
% expanded positions
'$module_expansion'(B,B1,BO,M,M,M,UVars). % expand body
% $trace_module((H:-B),(H:-B1)).
% expand module names in a body
'$prepare_body_with_correct_modules'(V,M,call(M:V)) :- var(V), !.
'$prepare_body_with_correct_modules'((A,B),M,(A1,B1)) :- !,
'$prepare_body_with_correct_modules'(A,M,A1),
'$prepare_body_with_correct_modules'(B,M,B1).
'$prepare_body_with_correct_modules'((A;B),M,(A1;B1)) :- !,
'$prepare_body_with_correct_modules'(A,M,A1),
'$prepare_body_with_correct_modules'(B,M,B1).
'$prepare_body_with_correct_modules'((A->B),M,(A1->B1)) :- !,
'$prepare_body_with_correct_modules'(A,M,A1),
'$prepare_body_with_correct_modules'(B,M,B1).
'$prepare_body_with_correct_modules'(true,_,true) :- !.
'$prepare_body_with_correct_modules'(fail,_,fail) :- !.
'$prepare_body_with_correct_modules'(false,_,false) :- !.
'$prepare_body_with_correct_modules'(M:G,_,M:G) :- !.
'$prepare_body_with_correct_modules'(G,M,G) :-
'$system_predicate'(G,M), !.
'$prepare_body_with_correct_modules'(G,M,M:G).
'$trace_module'(X) :-
telling(F),
tell('P0:debug'),
write(X),nl,
tell(F), fail.
'$trace_module'(_).
'$trace_module'(X,Y) :- X==Y, !.
'$trace_module'(X,Y) :-
telling(F),
tell('~/.dbg.modules'),
write('***************'), nl,
portray_clause(X),
portray_clause(Y),
tell(F),fail.
'$trace_module'(_,_).
%
% calling the meta-call expansion facility and expand_goal from
% a meta-call.
%
'$expand_goal'(G0, GoalMod, CurMod, G, NM) :-
'$expand_goal2'(G0,GoalMod,G1,NM),
( '$meta_expansion'(GoalMod, CurMod, G1, GF, []) ->
G = GF
;
G = G1
).
'$expand_goal2'(G, M, NG, NM) :-
'$undefined'(G,M),
functor(G,F,N),
recorded('$import','$import'(ExportingMod,M,F,N),_),
ExportingMod \= M,
!,
'$expand_goal2'(G, ExportingMod, NG, NM).
'$expand_goal2'(G, M, GF, M) :-
'$pred_goal_expansion_on',
% make sure we do not try to expand conjs, etc...
user:goal_expansion(G,M,GF0), !,
% allow recursive goal expansion
'$expand_goal2'(GF0,M,GF,M).
'$expand_goal2'(G, M, G, M).
% expand module names in a body
% args are:
% goals to expand
% code to pass to compiler
% code to pass to listing
% current module for looking up preds
% current module for fixing up meta-call arguments
% current module for predicate
% head variables.
'$module_expansion'(V,call(MM:V),call(MM:V),_M,MM,_TM,_) :- var(V), !.
'$module_expansion'((A,B),(A1,B1),(AO,BO),M,MM,TM,HVars) :- !,
'$module_expansion'(A,A1,AO,M,MM,TM,HVars),
'$module_expansion'(B,B1,BO,M,MM,TM,HVars).
'$module_expansion'((A;B),(A1;B1),(AO;BO),M,MM,TM,HVars) :- !,
'$module_expansion'(A,A1,AO,M,MM,TM,HVars),
'$module_expansion'(B,B1,BO,M,MM,TM,HVars).
'$module_expansion'((A|B),(A1|B1),(AO|BO),M,MM,TM,HVars) :- !,
'$module_expansion'(A,A1,AO,M,MM,TM,HVars),
'$module_expansion'(B,B1,BO,M,MM,TM,HVars).
'$module_expansion'((A->B),(A1->B1),(AO->BO),M,MM,TM,HVars) :- !,
'$module_expansion'(A,A1,AO,M,MM,TM,HVars),
'$module_expansion'(B,B1,BO,M,MM,TM,HVars).
'$module_expansion'(\+A,\+A1,\+AO,M,MM,TM,HVars) :- !,
'$module_expansion'(A,A1,AO,M,MM,TM,HVars).
'$module_expansion'(not(A),not(A1),not(AO),M,MM,TM,HVars) :- !,
'$module_expansion'(A,A1,AO,M,MM,TM,HVars).
'$module_expansion'(true,true,true,_,_,_,_) :- !.
'$module_expansion'(fail,fail,fail,_,_,_,_) :- !.
'$module_expansion'(false,false,false,_,_,_,_) :- !.
% if I don't know what the module is, I cannot do anything to the goal,
% so I just put a call for later on.
'$module_expansion'(M:G,call(M:G),call(M:G),_,_,_,_) :- var(M), !.
'$module_expansion'(M:G,G1,GO,_,_,TM,HVars) :-
'$module_expansion'(G,G1,GO,M,M,TM,HVars).
% if M1 is given explicitly process G within M1's context.
% '$module_expansion'(M:G,G1,GO,_Mod,_MM,TM,HVars) :- !,
% % is this imported from some other module M1?
% ( '$imported_pred'(G, M, M1) ->
% % continue recursively...
% '$module_expansion'(G,G1,GO,M1,M,TM,HVars)
% ;
% (
% '$meta_expansion'(M, M, G, NG, HVars)
% ;
% G = NG
% ),
% '$complete_goal_expansion'(NG, M, M, TM, G1, GO, HVars)
% ).
%
% next, check if this is something imported.
%
'$module_expansion'(G, G1, GO, CurMod, MM, TM, HVars) :-
% is this imported from some other module M1?
( '$imported_pred'(G, CurMod, M1) ->
'$module_expansion'(G, G1, GO, M1, MM, TM, HVars)
;
( '$meta_expansion'(CurMod, MM, G, GI, HVars)
;
GI = G
),
'$complete_goal_expansion'(GI, CurMod, MM, TM, G1, GO, HVars)
).
'$imported_pred'(G, ImportingMod, ExportingMod) :-
'$undefined'(G, ImportingMod),
functor(G,F,N),
recorded('$import','$import'(ExportingMod,ImportingMod,F,N),_),
ExportingMod \= ImportingMod.
% args are:
% goal to expand
% current module for looking up pred
% current module from top-level clause
% goal to pass to compiler
% goal to pass to listing
% head variables.
'$complete_goal_expansion'(G, M, CM, TM, G1, G2, HVars) :-
'$pred_goal_expansion_on',
user:goal_expansion(G,M,GI), !,
'$module_expansion'(GI,G1,G2,M,CM,TM,HVars).
'$complete_goal_expansion'(G, M, CM, TM, G1, G2, HVars) :-
'$system_predicate'(G,M), !,
'$c_built_in'(G,M,Gi),
(Gi \== G ->
'$module_expansion'(Gi,_,G2,M,CM,TM,HVars),
% make built-in processing transparent.
(TM = M -> G1 = G ; G1 = M:G)
; TM = M ->
G2 = G, G1 = G
;
G2 = M:G, G1 = M:G % atts:
).
'$complete_goal_expansion'(G, Mod, _, Mod, G, G, _) :- !.
'$complete_goal_expansion'(G, GMod, _, _, GMod:G, GMod:G, _).
% meta_predicate declaration
% records $meta_predicate(SourceModule,Functor,Arity,Declaration)
% directive now meta_predicate Ps :- $meta_predicate(Ps).
:- dynamic_predicate('$meta_predicate'/4,logical).
'$meta_predicate'((P,Ps), M) :- !,
'$meta_predicate'(P, M),
'$meta_predicate'(Ps, M).
'$meta_predicate'(M:D, _) :- !,
'$meta_predicate'(D, M).
'$meta_predicate'(P, M1) :-
'$install_meta_predicate'(P, M1).
'$install_meta_predicate'(P, M1) :-
functor(P,F,N),
( M1 = prolog -> M = _ ; M1 = M),
( retractall('$meta_predicate'(F,M,N,_)), fail ; true),
asserta(prolog:'$meta_predicate'(F,M,N,P)),
'$flags'(P, M1, Fl, Fl),
NFlags is Fl \/ 0x200000,
'$flags'(P, M1, Fl, NFlags).
% return list of vars in expanded positions on the head of a clause.
%
% these variables should not be expanded by meta-calls in the body of the goal.
%
'$module_u_vars'(H,UVars,M) :-
functor(H,F,N),
'$meta_predicate'(F,M,N,D), !,
'$module_u_vars'(N,D,H,UVars).
'$module_u_vars'(_,[],_).
'$module_u_vars'(0,_,_,[]) :- !.
'$module_u_vars'(I,D,H,[Y|L]) :-
arg(I,D,X), ( X=':' ; integer(X)),
arg(I,H,Y), var(Y), !,
I1 is I-1,
'$module_u_vars'(I1,D,H,L).
'$module_u_vars'(I,D,H,L) :-
I1 is I-1,
'$module_u_vars'(I1,D,H,L).
% expand arguments of a meta-predicate
% $meta_expansion(ModuleWhereDefined,CurrentModule,Goal,ExpandedGoal,MetaVariables)
'$meta_expansion'(Mod,MP,G,G1,HVars) :-
functor(G,F,N),
'$meta_predicate'(F,Mod,N,D), !,
functor(G1,F,N),
'$meta_expansion_loop'(N,D,G,G1,HVars,MP).
% format(user_error," gives ~w~n]",[G1]).
% expand argument
'$meta_expansion_loop'(0,_,_,_,_,_) :- !.
'$meta_expansion_loop'(I,D,G,G1,HVars,M) :-
arg(I,D,X), (X==':' ; integer(X)),
arg(I,G,A), '$do_expand'(A,HVars), !,
'$process_expanded_arg'(A, M, NA),
arg(I,G1,NA),
I1 is I-1,
'$meta_expansion_loop'(I1,D,G,G1,HVars,M).
'$meta_expansion_loop'(I,D,G,G1,HVars,M) :-
arg(I,G,A),
arg(I,G1,A),
I1 is I-1,
'$meta_expansion_loop'(I1,D,G,G1,HVars,M).
% check if an argument should be expanded
'$do_expand'(V,HVars) :- var(V), !, '$not_in_vars'(V,HVars).
'$do_expand'(_:_,_) :- !, fail.
'$do_expand'(_,_).
'$process_expanded_arg'(V, M, M:V) :- var(V), !.
'$process_expanded_arg'((V1,V2), M, (NV1,NV2)) :- !,
'$process_expanded_arg'(V1, M, NV1),
'$process_expanded_arg'(V2, M, NV2).
'$process_expanded_arg'((V1;V2), M, (NV1;NV2)) :- !,
'$process_expanded_arg'(V1, M, NV1),
'$process_expanded_arg'(V2, M, NV2).
'$process_expanded_arg'((V1|V2), M, (NV1|NV2)) :- !,
'$process_expanded_arg'(V1, M, NV1),
'$process_expanded_arg'(V2, M, NV2).
'$process_expanded_arg'((V1->V2), M, (NV1->NV2)) :- !,
'$process_expanded_arg'(V1, M, NV1),
'$process_expanded_arg'(V2, M, NV2).
'$process_expanded_arg'(\+V, M, \+NV) :- !,
'$process_expanded_arg'(V, M, NV).
'$process_expanded_arg'(M:A, _, M:A) :- !.
%'$process_expanded_arg'(G, M, G) :-
% '$system_predicate'(G,M), !.
'$process_expanded_arg'(A, M, M:A).
'$not_in_vars'(_,[]).
'$not_in_vars'(V,[X|L]) :- X\==V, '$not_in_vars'(V,L).
current_module(Mod) :-
'$all_current_modules'(Mod).
current_module(Mod,TFN) :-
'$all_current_modules'(Mod),
( recorded('$module','$module'(TFN,Mod,_Publics),_) -> true ; TFN = user ).
source_module(Mod) :-
'$current_module'(Mod).
'$member'(X,[X|_]) :- !.
'$member'(X,[_|L]) :- '$member'(X,L).
% comma has its own problems.
:- '$install_meta_predicate'((:,:), prolog).
:- meta_predicate
abolish(:),
abolish(:,+),
all(?,:,?),
assert(:),
assert(:,+),
assert_static(:),
asserta(:),
asserta(:,+),
asserta_static(:),
assertz(:),
assertz(:,+),
assertz_static(:),
bagof(?,:,?),
bb_get(:,-),
bb_put(:,+),
bb_delete(:,?),
bb_update(:,?,?),
call(:),
call_with_args(:),
call_with_args(:,?),
call_with_args(:,?,?),
call_with_args(:,?,?,?),
call_with_args(:,?,?,?,?),
call_with_args(:,?,?,?,?,?),
call_with_args(:,?,?,?,?,?,?),
call_with_args(:,?,?,?,?,?,?,?),
call_with_args(:,?,?,?,?,?,?,?,?),
call_with_args(:,?,?,?,?,?,?,?,?,?),
call_residue(:,?),
catch(:,+,:),
clause(:,?),
clause(:,?,?),
compile(:),
consult(:),
current_predicate(:),
current_predicate(?,:),
depth_bound_call(:,+),
ensure_loaded(:),
findall(?,:,?),
findall(?,:,?,?),
freeze(?,:),
hide_predicate(:),
if(:,:,:),
incore(:),
listing(:),
nospy(:),
not(:),
once(:),
phrase(:,?),
phrase(:,?,+),
predicate_property(:,?),
predicate_statistics(:,-,-,-),
on_exception(+,:,:),
reconsult(:),
retract(:),
retract(:,?),
retractall(:),
reconsult(:),
setof(?,:,?),
spy(:),
unknown(+,:),
use_module(:),
use_module(:,?),
use_module(?,:,?),
when(?,:),
^(+,:),
\+ : .
%
% if we are asserting something in somewhere else's module,
% we need this little bird.
%
% assert((a:g :- b)) then SICStus compiles this into the original module.
% YAP is not 100% compatible, as it will transform this into:
% a:assert(g :- user:b))
%
'$preprocess_clause_before_mod_change'((H:-B),M,M1,(H:-B1)) :-
'$module_u_vars'(H,UVars,M1),
'$preprocess_body_before_mod_change'(B,M,UVars,B1).
'$preprocess_body_before_mod_change'(V,M,_,call(M:V)) :- var(V), !.
'$preprocess_body_before_mod_change'((G1,G2),M,UVars,(NG1,NG2)) :- !,
'$preprocess_body_before_mod_change'(G1,M,UVars,NG1),
'$preprocess_body_before_mod_change'(G2,M,UVars,NG2).
'$preprocess_body_before_mod_change'((G1;G2),M,UVars,(NG1;NG2)) :- !,
'$preprocess_body_before_mod_change'(G1,M,UVars,NG1),
'$preprocess_body_before_mod_change'(G2,M,UVars,NG2).
'$preprocess_body_before_mod_change'((G1->G2),M,UVars,(NG1->NG2)) :- !,
'$preprocess_body_before_mod_change'(G1,M,UVars,NG1),
'$preprocess_body_before_mod_change'(G2,M,UVars,NG2).
'$preprocess_body_before_mod_change'(M:G,_,_,M:G) :- !.
'$preprocess_body_before_mod_change'(true,_,_,true) :- !.
'$preprocess_body_before_mod_change'(fail,_,_,fail) :- !.
'$preprocess_body_before_mod_change'(false,_,_,false) :- !.
'$preprocess_body_before_mod_change'(G,M,UVars,M:NG) :-
'$meta_expansion'(M, M, G, NG, UVars), !.
'$preprocess_body_before_mod_change'(G,M,_,G) :-
'$system_predicate'(G,M), !.
'$preprocess_body_before_mod_change'(G,M,_,M:G).