496 lines
14 KiB
Prolog
496 lines
14 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: corout.pl *
|
|
* Last rev: *
|
|
* mods: *
|
|
* comments: Coroutines implementation *
|
|
* *
|
|
*************************************************************************/
|
|
|
|
|
|
:- module('$coroutining',[
|
|
op(1150, fx, block)
|
|
%dif/2,
|
|
%when/2,
|
|
%block/1,
|
|
%wait/1,
|
|
%frozen/2
|
|
]).
|
|
|
|
:- use_system_module( '$_boot', ['$$compile'/4]).
|
|
|
|
:- use_system_module( '$_errors', ['$do_error'/2]).
|
|
|
|
:- use_system_module( attributes, [get_module_atts/2,
|
|
put_module_atts/2]).
|
|
|
|
|
|
attr_unify_hook(DelayList, _) :-
|
|
wake_delays(DelayList).
|
|
|
|
wake_delays([]).
|
|
wake_delays(Delay.List) :-
|
|
wake_delay(Delay),
|
|
wake_delays(List).
|
|
|
|
%
|
|
% Interface to attributed variables.
|
|
%
|
|
wake_delay(redo_dif(Done, X, Y)) :-
|
|
redo_dif(Done, X, Y).
|
|
wake_delay(redo_freeze(Done, V, Goal)) :-
|
|
redo_freeze(Done, V, Goal).
|
|
wake_delay(redo_eq(Done, X, Y, Goal)) :-
|
|
redo_eq(Done, X, Y, Goal, G).
|
|
wake_delay(redo_ground(Done, X, Goal)) :-
|
|
redo_ground(Done, X, Goal).
|
|
|
|
attribute_goals(Var) -->
|
|
{ get_attr(Var, '$coroutining', Delays) },
|
|
attgoal_for_delays(Delays, Var).
|
|
|
|
attgoal_for_delays([], V) --> [].
|
|
attgoal_for_delays([G|AllAtts], V) -->
|
|
attgoal_for_delay(G, V),
|
|
attgoal_for_delays(AllAtts, V).
|
|
|
|
attgoal_for_delay(redo_dif(Done, X, Y), V) -->
|
|
{ var(Done), first_att(dif(X,Y), V) }, !,
|
|
[prolog:dif(X,Y)].
|
|
attgoal_for_delay(redo_freeze(Done, V, Goal), V) -->
|
|
{ var(Done) }, !,
|
|
{ remove_when_declarations(Goal, NoWGoal) },
|
|
[ prolog:freeze(V,NoWGoal) ].
|
|
attgoal_for_delay(redo_eq(Done, X, Y, Goal), V) -->
|
|
{ var(Done), first_att(Goal, V) }, !,
|
|
[ prolog:when(X=Y,Goal) ].
|
|
attgoal_for_delay(redo_ground(Done, X, Goal), V) -->
|
|
{ var(Done) }, !,
|
|
[ prolog:when(ground(X),Goal) ].
|
|
attgoal_for_delay(_, V) --> [].
|
|
|
|
remove_when_declarations(when(Cond,Goal,_), when(Cond,NoWGoal)) :- !,
|
|
remove_when_declarations(Goal, NoWGoal).
|
|
remove_when_declarations(Goal, Goal).
|
|
|
|
%
|
|
% operators defined in this module:
|
|
%
|
|
prolog:freeze(V, G) :-
|
|
var(V), !,
|
|
freeze_goal(V,G).
|
|
prolog:freeze(_, G) :-
|
|
'$execute'(G).
|
|
|
|
freeze_goal(V,VG) :-
|
|
var(VG), !,
|
|
'$current_module'(M),
|
|
internal_freeze(V, redo_freeze(_Done,V,M:VG)).
|
|
freeze_goal(V,M:G) :- !,
|
|
internal_freeze(V, redo_freeze(_Done,V,M:G)).
|
|
freeze_goal(V,G) :-
|
|
'$current_module'(M),
|
|
internal_freeze(V, redo_freeze(_Done,V,M:G)).
|
|
|
|
%
|
|
%
|
|
% Dif is tricky because we need to wake up on the two variables being
|
|
% bound together, or on any variable of the term being bound to
|
|
% another. Also, the day YAP fully supports infinite rational trees,
|
|
% dif should work for them too. Hence, term comparison should not be
|
|
% implemented in Prolog.
|
|
%
|
|
% This is the way dif works. The '$can_unify' predicate does not know
|
|
% anything about dif semantics, it just compares two terms for
|
|
% equaility and is based on compare. If it succeeds without generating
|
|
% a list of variables, the terms are equal and dif fails. If it fails,
|
|
% dif succeeds.
|
|
%
|
|
% If it succeeds but it creates a list of variables, dif creates
|
|
% suspension records for all these variables on the '$redo_dif'(V,
|
|
% X, Y) goal. V is a flag that says whether dif has completed or not,
|
|
% X and Y are the original goals. Whenever one of these variables is
|
|
% bound, it calls '$redo_dif' again. '$redo_dif' will then check whether V
|
|
% was bound. If it was, dif has succeeded and redo_dif just
|
|
% exits. Otherwise, '$redo_dif' will call dif again to see what happened.
|
|
%
|
|
% Dif needs two extensions from the suspension engine:
|
|
%
|
|
% First, it needs
|
|
% for the engine to be careful when binding two suspended
|
|
% variables. Basically, in this case the engine must be sure to wake
|
|
% up one of the goals, as they may make dif fail. The way the engine
|
|
% does so is by searching the list of suspended variables, and search
|
|
% whether they share a common suspended goal. If they do, that
|
|
% suspended goal is added to the WokenList.
|
|
%
|
|
% Second, thanks to dif we may try to suspend on the same variable
|
|
% several times. dif calls a special version of freeze that checks
|
|
% whether that is in fact the case.
|
|
%
|
|
prolog:dif(X, Y) :-
|
|
'$can_unify'(X, Y, LVars), !,
|
|
LVars = [_|_],
|
|
dif_suspend_on_lvars(LVars, redo_dif(_Done, X, Y)).
|
|
prolog:dif(_, _).
|
|
|
|
|
|
dif_suspend_on_lvars([], _).
|
|
dif_suspend_on_lvars([H|T], G) :-
|
|
internal_freeze(H, G),
|
|
dif_suspend_on_lvars(T, G).
|
|
|
|
%
|
|
% This predicate is called whenever a variable dif was suspended on is
|
|
% bound. Note that dif may have already executed successfully.
|
|
%
|
|
% Three possible cases: dif has executed and Done is bound; we redo
|
|
% dif and the two terms either unify, hence we fail, or may unify, and
|
|
% we try to increase the number of suspensions; last, the two terms
|
|
% did not unify, we are done, so we succeed and bind the Done variable.
|
|
%
|
|
redo_dif(Done, _, _) :- nonvar(Done), !.
|
|
redo_dif(Done, X, Y) :-
|
|
'$can_unify'(X, Y, LVars), !,
|
|
LVars = [_|_],
|
|
dif_suspend_on_lvars(LVars, redo_dif(Done, X, Y)).
|
|
redo_dif('$done', _, _).
|
|
|
|
redo_freeze(Done, V, G0) :-
|
|
% If you called nonvar as condition for when, then you may find yourself
|
|
% here.
|
|
%
|
|
% someone else (that is Cond had ;) did the work, do nothing
|
|
%
|
|
(nonvar(Done) -> true ;
|
|
%
|
|
% We still have some more conditions: continue the analysis.
|
|
%
|
|
G0 = when(C, G, Done) -> when(C, G, Done) ;
|
|
%
|
|
% check if the variable was really bound
|
|
%
|
|
var(V) -> internal_freeze(V, redo_freeze(Done,V,G0)) ;
|
|
%
|
|
% I can't believe it: we're done and can actually execute our
|
|
% goal. Notice we have to say we are done, otherwise someone else in
|
|
% the disjunction might decide to wake up the goal themselves.
|
|
%
|
|
Done = '$done', '$execute'(G0) ).
|
|
|
|
%
|
|
% eq is a combination of dif and freeze
|
|
redo_eq(Done, _, _, _, _) :- nonvar(Done), !.
|
|
redo_eq(_, X, Y, _, G) :-
|
|
'$can_unify'(X, Y, LVars),
|
|
LVars = [_|_], !,
|
|
dif_suspend_on_lvars(LVars, G).
|
|
redo_eq(Done, _, _, when(C, G, Done), _) :- !,
|
|
when(C, G, Done).
|
|
redo_eq('$done', _ ,_ , Goal, _) :-
|
|
'$execute'(Goal).
|
|
|
|
%
|
|
% ground is similar to freeze
|
|
redo_ground(Done, _, _) :- nonvar(Done), !.
|
|
redo_ground(Done, X, Goal) :-
|
|
'$non_ground'(X, Var), !,
|
|
internal_freeze(Var, redo_ground(Done, X, Goal)).
|
|
redo_ground(Done, _, when(C, G, Done)) :- !,
|
|
when(C, G, Done).
|
|
redo_ground('$done', _, Goal) :-
|
|
'$execute'(Goal).
|
|
|
|
|
|
%
|
|
% support for when/2 built-in
|
|
%
|
|
prolog:when(Conds,Goal) :-
|
|
'$current_module'(Mod),
|
|
prepare_goal_for_when(Goal, Mod, ModG),
|
|
when(Conds, ModG, Done, [], LG), !,
|
|
%write(vsc:freezing(LG,Done)),nl,
|
|
suspend_when_goals(LG, Done).
|
|
prolog:when(_,Goal) :-
|
|
'$execute'(Goal).
|
|
|
|
%
|
|
% support for when/2 like declaration.
|
|
%
|
|
%
|
|
% when will block on a conjunction or disjunction of nonvar, ground,
|
|
% ?=, where ?= is both terms being bound together
|
|
%
|
|
%
|
|
'$declare_when'(Cond, G) :-
|
|
generate_code_for_when(Cond, G, Code),
|
|
'$current_module'(Module),
|
|
'$$compile'(Code, Code, 5, Module), fail.
|
|
'$declare_when'(_,_).
|
|
|
|
%
|
|
% use a meta interpreter for now
|
|
%
|
|
generate_code_for_when(Conds, G,
|
|
( G :- when(Conds, ModG, Done, [], LG), !,
|
|
suspend_when_goals(LG, Done)) ) :-
|
|
'$current_module'(Mod),
|
|
prepare_goal_for_when(G, Mod, ModG).
|
|
|
|
|
|
%
|
|
% make sure we have module info for G!
|
|
%
|
|
prepare_goal_for_when(G, Mod, Mod:call(G)) :- var(G), !.
|
|
prepare_goal_for_when(M:G, _, M:G) :- !.
|
|
prepare_goal_for_when(G, Mod, Mod:G).
|
|
|
|
|
|
%
|
|
% now for the important bit
|
|
%
|
|
|
|
% Done is used to synchronise: when it is bound someone else did the
|
|
% goal and we can give up.
|
|
%
|
|
% when/5 and when_suspend succeds when there is need to suspend a goal
|
|
%
|
|
%
|
|
when(V, G, Done, LG0, LGF) :- var(V), !,
|
|
'$do_error'(instantiation_error,when(V,G)).
|
|
when(nonvar(V), G, Done, LG0, LGF) :-
|
|
when_suspend(nonvar(V), G, Done, LG0, LGF).
|
|
when(?=(X,Y), G, Done, LG0, LGF) :-
|
|
when_suspend(?=(X,Y), G, Done, LG0, LGF).
|
|
when(ground(T), G, Done, LG0, LGF) :-
|
|
when_suspend(ground(T), G, Done, LG0, LGF).
|
|
when((C1, C2), G, Done, LG0, LGF) :-
|
|
% leave it open to continue with when.
|
|
(
|
|
when(C1, when(C2, G, Done), Done, LG0, LGI)
|
|
->
|
|
LGI = LGF
|
|
;
|
|
% we solved C1, great, now we just have to solve C2!
|
|
when(C2, G, Done, LG0, LGF)
|
|
).
|
|
when((G1 ; G2), G, Done, LG0, LGF) :-
|
|
when(G1, G, Done, LG0, LGI),
|
|
when(G2, G, Done, LGI, LGF).
|
|
|
|
%
|
|
% Auxiliary predicate called from within a conjunction.
|
|
% Repeat basic code for when, as inserted in first clause for predicate.
|
|
%
|
|
when(_, _, Done) :-
|
|
nonvar(Done), !.
|
|
when(Cond, G, Done) :-
|
|
when(Cond, G, Done, [], LG),
|
|
!,
|
|
suspend_when_goals(LG, Done).
|
|
when(_, G, '$done') :-
|
|
'$execute'(G).
|
|
|
|
%
|
|
% Do something depending on the condition!
|
|
%
|
|
% some one else did the work.
|
|
%
|
|
when_suspend(_, _, Done, _, []) :- nonvar(Done), !.
|
|
%
|
|
% now for the serious stuff.
|
|
%
|
|
when_suspend(nonvar(V), G, Done, LG0, LGF) :-
|
|
try_freeze(V, G, Done, LG0, LGF).
|
|
when_suspend(?=(X,Y), G, Done, LG0, LGF) :-
|
|
try_eq(X, Y, G, Done, LG0, LGF).
|
|
when_suspend(ground(X), G, Done, LG0, LGF) :-
|
|
try_ground(X, G, Done, LG0, LGF).
|
|
|
|
|
|
try_freeze(V, G, Done, LG0, LGF) :-
|
|
var(V),
|
|
LGF = ['$coroutining':internal_freeze(V, redo_freeze(Done, V, G))|LG0].
|
|
|
|
try_eq(X, Y, G, Done, LG0, LGF) :-
|
|
'$can_unify'(X, Y, LVars), LVars = [_|_],
|
|
LGF = ['$coroutining':dif_suspend_on_lvars(LVars, redo_eq(Done, X, Y, G))|LG0].
|
|
|
|
try_ground(X, G, Done, LG0, LGF) :-
|
|
'$non_ground'(X, Var), % the C predicate that succeds if
|
|
% finding out the term is nonground
|
|
% and gives the first variable it
|
|
% finds. Notice that this predicate
|
|
% must know about svars.
|
|
LGF = ['$coroutining':internal_freeze(Var, redo_ground(Done, X, G))| LG0].
|
|
|
|
%
|
|
% When executing a when, if nobody succeeded, we need to create suspensions.
|
|
%
|
|
suspend_when_goals([], _).
|
|
suspend_when_goals(['$coroutining':internal_freeze(V, G)|Ls], Done) :-
|
|
var(Done), !,
|
|
internal_freeze(V, G),
|
|
suspend_when_goals(Ls, Done).
|
|
suspend_when_goals([dif_suspend_on_lvars(LVars, G)|LG], Done) :-
|
|
var(Done), !,
|
|
dif_suspend_on_lvars(LVars, G),
|
|
suspend_when_goals(LG, Done).
|
|
suspend_when_goals([_|_], _).
|
|
|
|
%
|
|
% Support for wait declarations on goals.
|
|
% Or we also use the more powerful, SICStus like, "block" declarations.
|
|
%
|
|
% block or wait declarations must precede the first clause.
|
|
%
|
|
|
|
%
|
|
% I am using the simplest solution now: I'll add an extra clause at
|
|
% the beginning of the procedure to do this work. This creates a
|
|
% choicepoint and make things a bit slower, but it's probably not as
|
|
% significant as the remaining overheads.
|
|
%
|
|
prolog:'$block'(Conds) :-
|
|
generate_blocking_code(Conds, _, Code),
|
|
'$current_module'(Module),
|
|
'$$compile'(Code, Code, 5, Module), fail.
|
|
prolog:'$block'(_).
|
|
|
|
generate_blocking_code(Conds, G, Code) :-
|
|
extract_head_for_block(Conds, G),
|
|
recorded('$blocking_code','$code'(G,OldConds),R), !,
|
|
erase(R),
|
|
functor(G, Na, Ar),
|
|
'$current_module'(M),
|
|
abolish(M:Na, Ar),
|
|
generate_blocking_code((Conds,OldConds), G, Code).
|
|
generate_blocking_code(Conds, G, (G :- (If, !, when(When, G)))) :-
|
|
extract_head_for_block(Conds, G),
|
|
recorda('$blocking_code','$code'(G,Conds),_),
|
|
generate_body_for_block(Conds, G, If, When).
|
|
|
|
%
|
|
% find out what we are blocking on.
|
|
%
|
|
extract_head_for_block((C1, _), G) :- !,
|
|
extract_head_for_block(C1, G).
|
|
extract_head_for_block(C, G) :-
|
|
functor(C, Na, Ar),
|
|
functor(G, Na, Ar).
|
|
|
|
%
|
|
% If we suspend on the conditions, we should continue
|
|
% execution. If we don't suspend we should fail so that we can take
|
|
% the next clause. To
|
|
% know what we have to do we just test how many variables we suspended
|
|
% on ;-).
|
|
%
|
|
|
|
%
|
|
% We generate code as follows:
|
|
%
|
|
% block a(-,-,?)
|
|
%
|
|
% (var(A1), var(A2) -> true ; fail), !, when((nonvar(A1);nonvar(A2)),G).
|
|
%
|
|
% block a(-,-,?), a(?,-, -)
|
|
%
|
|
% (var(A1), var(A2) -> true ; (var(A2), var(A3) -> true ; fail)), !,
|
|
% when(((nonvar(A1);nonvar(A2)),(nonvar(A2);nonvar(A3))),G).
|
|
|
|
generate_body_for_block((C1, C2), G, (Code1 -> true ; Code2), (WhenConds,OtherWhenConds)) :- !,
|
|
generate_for_cond_in_block(C1, G, Code1, WhenConds),
|
|
generate_body_for_block(C2, G, Code2, OtherWhenConds).
|
|
generate_body_for_block(C, G, (Code -> true ; fail), WhenConds) :-
|
|
generate_for_cond_in_block(C, G, Code, WhenConds).
|
|
|
|
generate_for_cond_in_block(C, G, Code, Whens) :-
|
|
C =.. [_|Args],
|
|
G =.. [_|GArgs],
|
|
fetch_out_variables_for_block(Args,GArgs,L0Vars),
|
|
add_blocking_vars(L0Vars, LVars),
|
|
generate_for_each_arg_in_block(LVars, Code, Whens).
|
|
|
|
add_blocking_vars([], [_]) :- !.
|
|
add_blocking_vars(LV, LV).
|
|
|
|
fetch_out_variables_for_block([], [], []).
|
|
fetch_out_variables_for_block(['?'|Args], [_|GArgs], LV) :-
|
|
fetch_out_variables_for_block(Args, GArgs, LV).
|
|
fetch_out_variables_for_block(['-'|Args], [GArg|GArgs],
|
|
[GArg|LV]) :-
|
|
fetch_out_variables_for_block(Args, GArgs, LV).
|
|
|
|
generate_for_each_arg_in_block([], false, true).
|
|
generate_for_each_arg_in_block([V], var(V), nonvar(V)) :- !.
|
|
generate_for_each_arg_in_block([V|L], (var(V),If), (nonvar(V);Whens)) :-
|
|
generate_for_each_arg_in_block(L, If, Whens).
|
|
|
|
|
|
%
|
|
% The wait declaration is a simpler and more efficient version of block.
|
|
%
|
|
prolog:'$wait'(Na/Ar) :-
|
|
functor(S, Na, Ar),
|
|
arg(1, S, A),
|
|
'$current_module'(M),
|
|
'$$compile'((S :- var(A), !, freeze(A, S)), (S :- var(A), !, freeze(A, S)), 5, M), fail.
|
|
prolog:'$wait'(_).
|
|
|
|
prolog:frozen(V, LG) :-
|
|
var(V), !,
|
|
'$attributes':attvars_residuals([V], Gs, []),
|
|
simplify_frozen( Gs, SGs ),
|
|
list_to_conj( SGs, LG ).
|
|
prolog:frozen(V, G) :-
|
|
'$do_error'(uninstantiation_error(V),frozen(V,G)).
|
|
|
|
simplify_frozen( [prolog:freeze(_, G)|Gs], [G|NGs] ) :-
|
|
simplify_frozen( Gs,NGs ).
|
|
simplify_frozen( [prolog:when(_, G)|Gs], [G|NGs] ) :-
|
|
simplify_frozen( Gs,NGs ).
|
|
simplify_frozen( [prolog:dif(_, _)|Gs], NGs ) :-
|
|
simplify_frozen( Gs,NGs ).
|
|
simplify_frozen( [], [] ).
|
|
|
|
list_to_conj([], true).
|
|
list_to_conj([El], El).
|
|
list_to_conj([E,E1|Els], (E,C) ) :-
|
|
list_to_conj([E1|Els], C).
|
|
|
|
%internal_freeze(V,G) :-
|
|
% attributes:get_att(V, 0, Gs), write(G+Gs),nl,fail.
|
|
internal_freeze(V,G) :-
|
|
update_att(V, G).
|
|
|
|
update_att(V, G) :-
|
|
attributes:get_module_atts(V, '$coroutining'(_,Gs)),
|
|
not_vmember(G, Gs), !,
|
|
attributes:put_module_atts(V, '$coroutining'(_,[G|Gs])).
|
|
update_att(V, G) :-
|
|
attributes:put_module_atts(V, '$coroutining'(_,[G])).
|
|
|
|
|
|
not_vmember(_, []).
|
|
not_vmember(V, [V1|DonesSoFar]) :-
|
|
V \== V1,
|
|
not_vmember(V, DonesSoFar).
|
|
|
|
first_att(T, V) :-
|
|
term_variables(T, Vs),
|
|
check_first_attvar(Vs, V).
|
|
|
|
check_first_attvar(V.Vs, V0) :- attvar(V), !, V == V0.
|
|
check_first_attvar(_.Vs, V0) :-
|
|
check_first_attvar(Vs, V0).
|
|
|