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yap-6.3/pl/utils.yap
2011-07-11 07:40:43 -07:00

724 lines
18 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: utils.yap *
* Last rev: 8/2/88 *
* mods: *
* comments: Some utility predicates available in yap *
* *
*************************************************************************/
op(P,T,V) :-
'$check_op'(P,T,V,op(P,T,V)),
'$op'(P, T, V).
% just check the operator declarations for correctness.
'$check_op'(P,T,Op,G) :-
( var(P) ; var(T); var(Op)), !,
'$do_error'(instantiation_error,G).
'$check_op'(P,_,_,G) :-
\+ integer(P), !,
'$do_error'(type_error(integer,P),G).
'$check_op'(P,_,_,G) :-
P < 0, !,
'$do_error'(domain_error(operator_priority,P),G).
'$check_op'(P,_,_,G) :-
P > 1200, !,
'$do_error'(domain_error(operator_priority,P),G).
'$check_op'(_,T,_,G) :-
\+ atom(T), !,
'$do_error'(type_error(atom,P),G).
'$check_op'(_,T,_,G) :-
\+ '$associativity'(T), !,
'$do_error'(domain_error(operator_specifier,T),G).
'$check_op'(P,T,V,G) :-
'$check_module_for_op'(V, G, NV),
'$check_top_op'(P, T, NV, G).
'$check_top_op'(_, _, [], _).
'$check_top_op'(P, T, Op.NV, G) :- !,
'$check_ops'(P, T, Op.NV, G).
'$check_top_op'(P, T, V, G) :-
atom(V), !,
'$check_op_name'(P, T, V, G).
'$check_top_op'(P, T, V, G) :-
'$do_error'(type_error(atom,V),G).
'$associativity'(xfx).
'$associativity'(xfy).
'$associativity'(yfx).
'$associativity'(yfy).
'$associativity'(xf).
'$associativity'(yf).
'$associativity'(fx).
'$associativity'(fy).
'$check_module_for_op'(MOp, G, _) :-
var(MOp), !,
'$do_error'(instantiation_error,G).
'$check_module_for_op'(M:V, G, _) :-
var(M), !,
'$do_error'(instantiation_error,G).
'$check_module_for_op'(M:V, G, NV) :-
atom(M), !,
'$check_module_for_op'(V, G, NV).
'$check_module_for_op'(M:V, G, _) :- !,
'$do_error'(type_error(atom,P),G).
'$check_module_for_op'(V, G, V).
'$check_ops'(P, T, [], G) :- !.
'$check_ops'(P, T, Op.NV, G) :- !,
(
var(NV)
->
'$do_error'(instantiation_error,G)
;
'$check_module_for_op'(Op, G, NOp),
'$check_op_name'(P, T, NOp, G),
'$check_ops'(P, T, NV, G)
).
'$check_ops'(P, T, Ops, G) :-
'$do_error'(type_error(list,Ops),G).
'$check_op_name'(_,_,V,G) :-
var(V), !,
'$do_error'(instantiation_error,G).
'$check_op_name'(_,_,',',G) :- !,
'$do_error'(permission_error(modify,operator,','),G).
'$check_op_name'(_,_,'[]',G) :- !,
'$do_error'(permispsion_error(create,operator,'[]'),G).
'$check_op_name'(_,_,'{}',G) :- !,
'$do_error'(permission_error(create,operator,'{}'),G).
'$check_op_name'(P,T,'|',G) :-
(
integer(P),
P < 1001
;
atom_codes(T,[_,_])
), !,
'$do_error'(permission_error(create,operator,'|'),G).
'$check_op_name'(_,_,V,_) :-
atom(V), !.
'$check_op_name'(_,_,A,G) :-
'$do_error'(type_error(atom,A),G).
'$op'(P, T, ML) :-
strip_module(ML, M, [A|As]), !,
'$opl'(P, T, M, [A|As]).
'$op'(P, T, A) :-
'$op2'(P,T,A).
'$opl'(P, T, _, []).
'$opl'(P, T, M, [A|As]) :-
'$op2'(P, T, M:A),
'$opl'(P, T, M, As).
'$op2'(P,T,A) :-
atom(A), !,
'$opdec'(P,T,A,prolog).
'$op2'(P,T,A) :-
strip_module(A,M,N),
'$opdec'(P,T,N,M).
current_op(X,Y,V) :- var(V), !,
'$current_module'(M),
'$do_current_op'(X,Y,V,M).
current_op(X,Y,M:Z) :- !,
'$current_opm'(X,Y,Z,M).
current_op(X,Y,Z) :-
'$current_module'(M),
'$do_current_op'(X,Y,Z,M).
'$current_opm'(X,Y,Z,M) :-
nonvar(Y),
\+ '$associativity'(Y),
'$do_error'(domain_error(operator_specifier,Y),current_op(X,Y,M:Z)).
'$current_opm'(X,Y,Z,M) :-
var(Z), !,
'$do_current_op'(X,Y,Z,M).
'$current_opm'(X,Y,M:Z,_) :- !,
'$current_opm'(X,Y,Z,M).
'$current_opm'(X,Y,Z,M) :-
'$do_current_op'(X,Y,Z,M).
'$do_current_op'(X,Y,Z,M) :-
nonvar(Y),
\+ '$associativity'(Y),
'$do_error'(domain_error(operator_specifier,Y),current_op(X,Y,M:Z)).
'$do_current_op'(X,Y,Z,M) :-
atom(Z), !,
'$current_atom_op'(Z, M1, Prefix, Infix, Posfix),
( M1 = prolog -> true ; M1 = M ),
(
'$get_prefix'(Prefix, X, Y)
;
'$get_infix'(Infix, X, Y)
;
'$get_posfix'(Posfix, X, Y)
).
'$do_current_op'(X,Y,Z,M) :-
'$current_op'(Z, M1, Prefix, Infix, Posfix),
( M1 = prolog -> true ; M1 = M ),
(
'$get_prefix'(Prefix, X, Y)
;
'$get_infix'(Infix, X, Y)
;
'$get_posfix'(Posfix, X, Y)
).
'$get_prefix'(Prefix, X, Y) :-
Prefix > 0,
X is Prefix /\ 0xfff,
(
0x2000 /\ Prefix =:= 0x2000
->
Y = fx
;
Y = fy
).
'$get_infix'(Infix, X, Y) :-
Infix > 0,
X is Infix /\ 0xfff,
(
0x3000 /\ Infix =:= 0x3000
->
Y = xfx
;
0x1000 /\ Infix =:= 0x1000
->
Y = xfy
;
Y = yfx
).
'$get_posfix'(Posfix, X, Y) :-
Posfix > 0,
X is Posfix /\ 0xfff,
(
0x1000 /\ Posfix =:= 0x1000
->
Y = xf
;
Y = yf
).
%%% Operating System utilities
cd :-
cd('~').
cd(F) :-
absolute_file_name(F, Dir, [file_type(directory),file_errors(fail),access(execute),expand(true)]),
working_directory(_, Dir).
getcwd(Dir) :- working_directory(Dir, Dir).
ls :-
getcwd(X),
'$load_system_ls'(X,L),
'$do_print_files'(L).
'$load_system_ls'(X,L) :-
'$undefined'(directory_files(X, L), operating_system_support),
load_files(library(system),[silent(true)]),
fail.
'$load_system_ls'(X,L) :-
operating_system_support:directory_files(X, L).
'$do_print_files'([]) :-
nl.
'$do_print_files'([F| Fs]) :-
'$do_print_file'(F),
'$do_print_files'(Fs).
'$do_print_file'('.') :- !.
'$do_print_file'('..') :- !.
'$do_print_file'(F) :- atom_concat('.', _, F), !.
'$do_print_file'(F) :-
write(F), write(' ').
pwd :-
getcwd(X),
write(X), nl.
unix(V) :- var(V), !,
'$do_error'(instantiation_error,unix(V)).
unix(argv(L)) :- '$is_list_of_atoms'(L,L), !, '$argv'(L).
unix(argv(V)) :-
'$do_error'(type_error(atomic,V),unix(argv(V))).
unix(cd) :- cd('~').
unix(cd(A)) :- cd(A).
unix(environ(X,Y)) :- '$do_environ'(X,Y).
unix(getcwd(X)) :- getcwd(X).
unix(shell(V)) :- var(V), !,
'$do_error'(instantiation_error,unix(shell(V))).
unix(shell(A)) :- atom(A), !, '$shell'(A).
unix(shell(V)) :-
'$do_error'(type_error(atomic,V),unix(shell(V))).
unix(system(V)) :- var(V), !,
'$do_error'(instantiation_error,unix(system(V))).
unix(system(A)) :- atom(A), !, system(A).
unix(system(V)) :-
'$do_error'(type_error(atom,V),unix(system(V))).
unix(shell) :- sh.
unix(putenv(X,Y)) :- '$putenv'(X,Y).
'$is_list_of_atoms'(V,_) :- var(V),!.
'$is_list_of_atoms'([],_) :- !.
'$is_list_of_atoms'([H|L],L0) :- !,
'$check_if_head_may_be_atom'(H,L0),
'$is_list_of_atoms'(L,L0).
'$is_list_of_atoms'(H,L0) :-
'$do_error'(type_error(list,H),unix(argv(L0))).
'$check_if_head_may_be_atom'(H,_) :-
var(H), !.
'$check_if_head_may_be_atom'(H,_) :-
atom(H), !.
'$check_if_head_may_be_atom'(H,L0) :-
'$do_error'(type_error(atom,H),unix(argv(L0))).
'$do_environ'(X, Y) :-
var(X), !,
'$do_error'(instantiation_error,unix(environ(X,Y))).
'$do_environ'(X, Y) :- atom(X), !,
'$getenv'(X,Y).
'$do_environ'(X, Y) :-
'$do_error'(type_error(atom,X),unix(environ(X,Y))).
putenv(Na,Val) :-
'$putenv'(Na,Val).
getenv(Na,Val) :-
'$getenv'(Na,Val).
setenv(Na,Val) :-
'$putenv'(Na,Val).
%%% Saving and restoring a computation
save(A) :- save(A,_).
save(A,_) :- var(A), !,
'$do_error'(instantiation_error,save(A)).
save(A,OUT) :- atom(A), !, atom_codes(A,S), '$save'(S,OUT).
save(S,OUT) :- '$save'(S,OUT).
save_program(A) :- var(A), !,
'$do_error'(instantiation_error,save_program(A)).
save_program(A) :- atom(A), !,
atom_codes(A,S),
'$save_program2'(S, true).
save_program(S) :- '$save_program2'(S, true).
save_program(A, G) :- var(A), !,
'$do_error'(instantiation_error, save_program(A,G)).
save_program(A, G) :- var(G), !,
'$do_error'(instantiation_error, save_program(A,G)).
save_program(A, G) :- \+ callable(G), !,
'$do_error'(type_error(callable,G), save_program(A,G)).
save_program(A, G) :-
( atom(A) -> atom_codes(A,S) ; A = S),
'$save_program2'(S, G),
fail.
save_program(_,_).
'$save_program2'(S,G) :-
(
G == true
->
true
;
recorda('$restore_goal', G ,R)
),
(
'$undefined'(reload_foreign_libraries, shlib)
->
true
;
recorda('$reload_foreign_libraries', true, R1)
),
'$save_program'(S),
(
var(R1)
->
true
;
erase(R1)
),
(
var(R)
->
true
;
erase(R)
),
fail.
'$save_program2'(_,_).
restore(A) :- var(A), !,
'$do_error'(instantiation_error,restore(A)).
restore(A) :- atom(A), !, name(A,S), '$restore'(S).
restore(S) :- '$restore'(S).
prolog :-
'$live'.
%%% current ....
recordaifnot(K,T,R) :-
recorded(K,T,R), % force non-det binding to R.
'$still_variant'(R,T),
!,
fail.
recordaifnot(K,T,R) :-
recorda(K,T,R).
recordzifnot(K,T,R) :-
recorded(K,T,R),
'$still_variant'(R,T),
!,
fail.
recordzifnot(K,T,R) :-
recordz(K,T,R).
current_atom(A) :- % check
atom(A), !.
current_atom(A) :- % generate
'$current_atom'(A).
current_atom(A) :- % generate
'$current_wide_atom'(A).
atom_concat(X,Y,At) :-
(
nonvar(X), nonvar(Y)
->
atom_concat([X,Y],At)
;
atom(At) ->
'$atom_contact_split'(At,X,Y)
;
var(At) ->
'$do_error'(instantiation_error,atom_concat(X,Y,At))
;
'$do_error'(type_error(atom,At),atomic_concat(X,Y,At))
).
'$atom_contact_split'(At,X,Y) :-
nonvar(X), !,
atom_codes(At, Codes),
atom_codes(X, Xs),
lists:append(Xs,Ys,Codes),
atom_codes(Y, Ys).
'$atom_contact_split'(At,X,Y) :-
nonvar(Y), !,
atom_codes(At, Codes),
atom_codes(Y, Ys),
once(lists:append(Xs,Ys,Codes)),
atom_codes(X, Xs).
'$atom_contact_split'(At,X,Y) :-
atom_codes(At, Codes),
lists:append(Xs, Ys, Codes),
atom_codes(X, Xs),
atom_codes(Y, Ys).
atomic_list_concat(L,At) :-
atomic_concat(L, At).
atomic_list_concat(L, El, At) :-
var(El), !,
'$do_error'(instantiation_error,atom_list_concat(L,El,At)).
atomic_list_concat(L, El, At) :-
nonvar(L), !,
'$add_els'(L,El,LEl),
atomic_concat(LEl, At).
atomic_list_concat(L, El, At) :-
nonvar(At), !,
atom_codes(At, S),
atom_codes(El, [ElS]),
'$split_elements'(S, ElS, SubS),
'$atomify_list'(SubS, L).
'$add_els'([A,B|L],El,[A,El|NL]) :- !,
'$add_els'([B|L],El,NL).
'$add_els'(L,_,L).
'$split_elements'(E.S, E, SubS) :- !,
'$split_elements'(S, E, SubS).
'$split_elements'(E1.S, E, [E1|L].SubS) :- !,
'$split_elements'(S, E, L, SubS).
'$split_elements'([], _, []).
'$split_elements'([], _, [], []).
'$split_elements'(E.S, E, [], SubS) :- !,
'$split_elements'(S, E, SubS).
'$split_elements'(E1.S, E, E1.L, SubS) :-
'$split_elements'(S, E, L, SubS).
'$atomify_list'([], []).
'$atomify_list'(S.SubS, A.L) :-
atom_codes(A, S),
'$atomify_list'(SubS, L).
atomic_concat(X,Y,At) :-
(
nonvar(X), nonvar(Y)
->
atomic_concat([X,Y],At)
;
atom(At) ->
atom_length(At,Len),
'$atom_contact_split'(At,X,Y)
;
number(At) ->
'$number_contact_split'(At,X,Y)
;
var(At) ->
'$do_error'(instantiation_error,atomic_concat(X,Y,At))
;
'$do_error'(type_error(atomic,At),atomic_concat(X,Y,At))
).
'$number_contact_split'(At,X,Y) :-
nonvar(X), !,
number_codes(At, Codes),
name(X, Xs),
lists:append(Xs,Ys,Codes),
name(Y, Ys).
'$number_contact_split'(At,X,Y) :-
nonvar(Y), !,
number_codes(At, Codes),
name(Y, Ys),
once(lists:append(Xs,Ys,Codes)),
name(X, Xs).
'$number_contact_split'(At,X,Y) :-
number_codes(At, Codes),
lists:append(Xs, Ys, Codes),
name(X, Xs),
name(Y, Ys).
sub_atom(At, Bef, Size, After, SubAt) :-
% extract something from an atom
atom(At), integer(Bef), integer(Size), !,
'$sub_atom_extract'(At, Bef, Size, After, SubAt).
sub_atom(At, Bef, Size, After, SubAt) :-
% extract subatom from an atom
atom(At), atom(SubAt), !,
'$sub_atom_fetch'(At, Bef, Size, After, SubAt).
sub_atom(At, Bef, Size, After, SubAt) :-
atom(At), !,
atom_codes(At, Atl),
'$sub_atom2'(Bef, Atl, Size, After, SubAt, sub_atom(At, Bef, Size, After, SubAt)).
sub_atom(At, Bef, Size, After, SubAt) :-
var(At), !,
'$do_error'(instantiation_error,sub_atom(At, Bef, Size,After, SubAt)).
sub_atom(At, Bef, Size, After, SubAt) :-
\+ atom(At), !,
'$do_error'(type_error(atom,At),sub_atom(At, Bef, Size,After, SubAt)).
'$sub_atom2'(Bef, Atl, Size, After, SubAt, ErrorTerm) :-
var(Bef), !,
'$sub_atombv'(Bef, Size, After, SubAt, Atl, ErrorTerm).
'$sub_atom2'(Bef, Atl, Size, After, SubAt, ErrorTerm) :-
'$sub_atom_get_subchars'(Bef, Atl, NewAtl),
'$sub_atom3'(Size, After, SubAt, NewAtl, ErrorTerm).
% if SubAt is bound, the rest is deterministic.
'$sub_atom3'(Size, After, SubAt, Atl, ErrorTerm) :-
nonvar(SubAt), !,
'$sub_atom_needs_atom'(SubAt,ErrorTerm),
'$sub_atom_needs_int'(Size,ErrorTerm),
'$sub_atom_needs_int'(After,ErrorTerm),
atom_codes(SubAt,Atls),
'$$_length1'(Atls, 0, Size),
'$sub_atom_get_subchars_and_match'(Size, Atl, Atls, NAtl),
'$$_length1'(NAtl,0,After).
% SubAt is unbound, but Size is bound
'$sub_atom3'(Size, After, SubAt, Atl, ErrorTerm) :-
nonvar(Size), !,
'$sub_atom_needs_int'(Size,ErrorTerm),
'$sub_atom_needs_int'(After,ErrorTerm),
'$sub_atom_get_subchars_and_match'(Size, Atl, SubAts, NAtl),
'$$_length1'(NAtl,0,After),
atom_codes(SubAt,SubAts).
% SubAt and Size are unbound, but After is bound.
'$sub_atom3'(Size, After, SubAt, Atl, ErrorTerm) :-
nonvar(After), !,
'$sub_atom_needs_int'(After,ErrorTerm),
'$sub_atom_get_last_subchars'(Atl,SubAts,After,Total,Size),
Total >= After,
atom_codes(SubAt,SubAts).
% SubAt, Size, and After are unbound.
'$sub_atom3'(Size, After, SubAt, Atl, _) :-
'$$_length1'(Atl,0,Len),
'$sub_atom_split'(Atl,Len,SubAts,Size,_,After),
atom_codes(SubAt,SubAts).
% Bef is unbound, so we've got three hypothesis
% ok: in the best case we just try to find SubAt in the original atom.
'$sub_atombv'(Bef, Size, After, SubAt, Atl, ErrorTerm) :-
nonvar(SubAt), !,
'$sub_atom_needs_atom'(SubAt, ErrorTerm),
atom_codes(SubAt,SubAts),
'$sub_atom_search'(SubAts, Atl, 0, Bef, AfterS),
'$$_length1'(SubAts, 0, Size),
'$$_length1'(AfterS, 0, After).
% ok: in the second best case we just get rid of the tail
'$sub_atombv'(Bef, Size, After, SubAt, Atl, ErrorTerm) :-
nonvar(After), !,
'$sub_atom_needs_int'(After, ErrorTerm),
'$sub_atom_get_last_subchars'(Atl,SubAt0,After,Total,Size0),
Total >= After,
'$sub_atom_split'(SubAt0,Size0,_,Bef,SubAts,Size),
atom_codes(SubAt,SubAts).
% ok: just do everything
'$sub_atombv'(Bef, Size, After, SubAt, Atl, _) :-
'$$_length1'(Atl, 0, Len),
'$sub_atom_split'(Atl,Len,_,Bef,Atls2,Len2),
'$sub_atom_split'(Atls2,Len2,SubAts,Size,_,After),
atom_codes(SubAt,SubAts).
'$sub_atom_search'([], AfterS, BefSize, BefSize, AfterS).
'$sub_atom_search'([C|SubAts], [C|Atl], BefSize, BefSize, AfterS) :-
'$sub_atom_search2'(SubAts, Atl, AfterS).
'$sub_atom_search'([C|SubAts], [_|Atl], BefSize, BefSizeF, AfterS) :-
NBefSize is BefSize+1,
'$sub_atom_search'([C|SubAts], Atl, NBefSize, BefSizeF, AfterS).
'$sub_atom_search2'([], AfterS, AfterS).
'$sub_atom_search2'([C|SubAts], [C|Atl], AfterS) :-
'$sub_atom_search2'(SubAts, Atl, AfterS).
'$sub_atom_get_subchars'(0, Atl, Atl) :- !.
'$sub_atom_get_subchars'(I0, [_|Atl], NAtl) :-
I is I0-1,
'$sub_atom_get_subchars'(I, Atl, NAtl).
'$sub_atom_get_subchars'(0, Atl, [], Atl) :- !.
'$sub_atom_get_subchars'(I0, [C|Atl], [C|L], NAtl) :-
I is I0-1,
'$sub_atom_get_subchars'(I, Atl, L, NAtl).
'$sub_atom_get_subchars_and_match'(0, Atl, [], Atl) :- !.
'$sub_atom_get_subchars_and_match'(I0, [C|Atl], [C|Match], NAtl) :-
I is I0-1,
'$sub_atom_get_subchars_and_match'(I, Atl, Match, NAtl).
'$sub_atom_check_length'([],0).
'$sub_atom_check_length'([_|L],N1) :-
N1 > 0,
N is N1-1,
'$sub_atom_check_length'(L,N).
'$sub_atom_get_last_subchars'([],[],_,0,0).
'$sub_atom_get_last_subchars'([C|Atl],SubAt,After,Total,Size) :-
'$sub_atom_get_last_subchars'(Atl,SubAt0,After,Total0,Size0),
Total is Total0+1,
( Total > After ->
Size is Size0+1, SubAt = [C|SubAt0]
;
Size = Size0, SubAt = SubAt0
).
'$sub_atom_split'(Atl,After,[],0,Atl,After).
'$sub_atom_split'([C|Atl],Len,[C|Atls],Size,NAtl,After) :-
Len1 is Len-1,
'$sub_atom_split'(Atl,Len1,Atls,Size0,NAtl,After),
Size is Size0+1.
'$sub_atom_needs_int'(V,_) :- var(V), !.
'$sub_atom_needs_int'(I,_) :- integer(I), I >= 0, !.
'$sub_atom_needs_int'(I,ErrorTerm) :- integer(I), !,
'$do_error'(domain_error(not_less_than_zero,I),ErrorTerm).
'$sub_atom_needs_int'(I,ErrorTerm) :-
'$do_error'(type_error(integer,I),ErrorTerm).
'$sub_atom_needs_atom'(V,_) :- var(V), !.
'$sub_atom_needs_atom'(A,_) :- atom(A), !.
'$sub_atom_needs_atom'(A,ErrorTerm) :-
'$do_error'(type_error(atom,A),ErrorTerm).
'$singletons_in_term'(T,VL) :-
'$variables_in_term'(T,[],V10),
'$sort'(V10, V1),
'$non_singletons_in_term'(T,[],V20),
'$sort'(V20, V2),
'$subtract_lists_of_variables'(V2,V1,VL).
'$subtract_lists_of_variables'([],VL,VL).
'$subtract_lists_of_variables'([_|_],[],[]) :- !.
'$subtract_lists_of_variables'([V1|VL1],[V2|VL2],VL) :-
V1 == V2, !,
'$subtract_lists_of_variables'(VL1,VL2,VL).
'$subtract_lists_of_variables'([V1|VL1],[V2|VL2],[V2|VL]) :-
'$subtract_lists_of_variables'([V1|VL1],VL2,VL).
simple(V) :- var(V), !.
simple(A) :- atom(A), !.
simple(N) :- number(N).
callable(V) :- var(V), !, fail.
callable(V) :- atom(V), !.
callable(V) :- functor(V,_,Ar), Ar > 0.
nth_instance(Key,Index,Ref) :-
nonvar(Key), var(Index), var(Ref), !,
recorded(Key,_,Ref),
'$nth_instance'(_,Index,Ref).
nth_instance(Key,Index,Ref) :-
'$nth_instance'(Key,Index,Ref).
nth_instance(Key,Index,T,Ref) :-
nonvar(Key), var(Index), var(Ref), !,
recorded(Key,T,Ref),
'$nth_instance'(_,Index,Ref).
nth_instance(Key,Index,T,Ref) :-
'$nth_instance'(Key,Index,Ref),
instance(Ref,T).
nb_current(GlobalVariable, Val) :-
'$nb_current'(GlobalVariable),
nb_getval(GlobalVariable, Val).
'$getval_exception'(GlobalVariable, Val, Caller) :-
user:exception(undefined_global_variable, GlobalVariable, Action),
!,
(
Action == fail
->
fail
;
Action == retry
->
b_getval(GlobalVariable, Val)
;
Action == error
->
'$do_error'(existence_error(variable, GlobalVariable),Caller)
;
'$do_error'(type_error(atom, Action),Caller)
).
subsumes_term(A,B) :-
\+ \+ terms:subsumes(A,B).