/* Part of SWI-Prolog Author: Jan Wielemaker E-mail: J.Wielemaker@vu.nl WWW: http://www.swi-prolog.org Copyright (c) 2004-2016, University of Amsterdam VU University Amsterdam All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ :- module('$attvar', [ '$wakeup'/1, % +Wakeup list freeze/2, % +Var, :Goal frozen/2, % @Var, -Goal call_residue_vars/2, % :Goal, -Vars copy_term/3 % +Term, -Copy, -Residue ]). /** Attributed variable handling Attributed variable and coroutining support based on attributed variables. This module is complemented with C-defined predicates defined in pl-attvar.c */ %! '$wakeup'(+List) % % Called from the kernel if assignments have been made to % attributed variables. '$wakeup'([]). '$wakeup'(wakeup(Attribute, Value, Rest)) :- call_all_attr_uhooks(Attribute, Value), '$wakeup'(Rest). call_all_attr_uhooks([], _). call_all_attr_uhooks(att(Module, AttVal, Rest), Value) :- uhook(Module, AttVal, Value), call_all_attr_uhooks(Rest, Value). %! uhook(+AttributeName, +AttributeValue, +Value) % % Run the unify hook for attributed named AttributeName after % assigning an attvar with attribute AttributeValue the value % Value. % % This predicate deals with reserved attribute names to avoid % the meta-call overhead. uhook(freeze, Goal, Y) :- !, ( attvar(Y) -> ( get_attr(Y, freeze, G2) -> put_attr(Y, freeze, '$and'(G2, Goal)) ; put_attr(Y, freeze, Goal) ) ; unfreeze(Goal) ). uhook(Module, AttVal, Value) :- Module:attr_unify_hook(AttVal, Value). %! unfreeze(+ConjunctionOrGoal) % % Handle unfreezing of conjunctions. As meta-calling control % structures is slower than meta-interpreting them we do this in % Prolog. Another advantage is that having unfreeze/1 in between % makes the stacktrace and profiling easier to intepret. Please % note that we cannot use a direct conjunction as this would break % freeze(X, (a, !, b)). unfreeze('$and'(A,B)) :- !, unfreeze(A), unfreeze(B). unfreeze(Goal) :- Goal. %! freeze(@Var, :Goal) % % Suspend execution of Goal until Var is unbound. :- meta_predicate freeze(?, 0). freeze(Var, Goal) :- '$freeze'(Var, Goal), !. % Succeeds if delayed freeze(_, Goal) :- Goal. %! frozen(@Var, -Goals) % % Unify Goals with the goals frozen on Var or true if no % goals are grozen on Var. frozen(Var, Goals) :- get_attr(Var, freeze, Goals0), !, make_conjunction(Goals0, Goals). frozen(_, true). make_conjunction('$and'(A0, B0), (A, B)) :- !, make_conjunction(A0, A), make_conjunction(B0, B). make_conjunction(G, G). /******************************* * PORTRAY * *******************************/ %! portray_attvar(@Var) % % Called from write_term/3 using the option attributes(portray) or % when the prolog flag write_attributes equals portray. Its task % is the write the attributes in a human readable format. :- public portray_attvar/1. portray_attvar(Var) :- write('{'), get_attrs(Var, Attr), portray_attrs(Attr, Var), write('}'). portray_attrs([], _). portray_attrs(att(Name, Value, Rest), Var) :- portray_attr(Name, Value, Var), ( Rest == [] -> true ; write(', '), portray_attrs(Rest, Var) ). portray_attr(freeze, Goal, Var) :- !, format('freeze(~w, ~W)', [ Var, Goal, [ portray(true), quoted(true), attributes(ignore) ] ]). portray_attr(Name, Value, Var) :- G = Name:attr_portray_hook(Value, Var), ( '$c_current_predicate'(_, G), G -> true ; format('~w = ...', [Name]) ). /******************************* * CALL RESIDUE * *******************************/ %! call_residue_vars(:Goal, -Vars) % % If Goal is true, Vars is the set of residual attributed % variables created by Goal. Goal is called as in call/1. This % predicate is for debugging constraint programs. Assume a % constraint program that creates conflicting constraints on a % variable that is not part of the result variables of Goal. If % the solver is powerful enough it will detect the conflict and % fail. If the solver is too weak however it will succeed and % residual attributed variables holding the conflicting constraint % form a witness of this problem. :- meta_predicate call_residue_vars(0, -). call_residue_vars(Goal, Vars) :- prolog_current_choice(Chp), setup_call_cleanup( '$call_residue_vars_start', run_crv(Goal, Chp, Vars, Det), '$call_residue_vars_end'), ( Det == true -> ! ; true ). call_residue_vars(_, _) :- fail. run_crv(Goal, Chp, Vars, Det) :- call(Goal), deterministic(Det), '$attvars_after_choicepoint'(Chp, Vars). %! copy_term(+Term, -Copy, -Gs) is det. % % Creates a regular term Copy as a copy of Term (without any % attributes), and a list Gs of goals that when executed reinstate % all attributes onto Copy. The nonterminal attribute_goals//1, as % defined in the modules the attributes stem from, is used to % convert attributes to lists of goals. copy_term(Term, Copy, Gs) :- term_attvars(Term, Vs), ( Vs == [] -> Gs = [], copy_term(Term, Copy) ; findall(Term-Gs, ( phrase(attvars_residuals(Vs), Gs), delete_attributes(Term) ), [Copy-Gs]) ). attvars_residuals([]) --> []. attvars_residuals([V|Vs]) --> ( { get_attrs(V, As) } -> attvar_residuals(As, V) ; [] ), attvars_residuals(Vs). attvar_residuals([], _) --> []. attvar_residuals(att(Module,Value,As), V) --> ( { nonvar(V) } -> % a previous projection predicate could have instantiated % this variable, for example, to avoid redundant goals [] ; ( { Module == freeze } -> frozen_residuals(Value, V) ; { current_predicate(Module:attribute_goals//1), phrase(Module:attribute_goals(V), Goals) } -> list(Goals) ; [put_attr(V, Module, Value)] ) ), attvar_residuals(As, V). list([]) --> []. list([L|Ls]) --> [L], list(Ls). delete_attributes(Term) :- term_attvars(Term, Vs), delete_attributes_(Vs). delete_attributes_([]). delete_attributes_([V|Vs]) :- del_attrs(V), delete_attributes_(Vs). %! frozen_residuals(+FreezeAttr, +Var)// is det. % % Instantiate a freeze goal for each member of the $and % conjunction. Note that we cannot map this into a conjunction % because freeze(X, a), freeze(X, !) would create freeze(X, % (a,!)), which is fundamentally different. We could create % freeze(X, (call(a), call(!))) or preform a more eleborate % analysis to validate the semantics are not changed. frozen_residuals('$and'(X,Y), V) --> !, frozen_residuals(X, V), frozen_residuals(Y, V). frozen_residuals(X, V) --> [ freeze(V, X) ].