/* Part of SWI-Prolog Author: Benoit Desouter Jan Wielemaker (SWI-Prolog port) Copyright (c) 2016, Benoit Desouter 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(tabling, [ (table)/1, % +PI ... current_table/2, % :Variant, ?Table abolish_all_tables/0, abolish_table_subgoals/1, % :Subgoal start_tabling/2, % +Wrapper, :Worker. op(1150, fx, table) ]). :- use_module(library(error)). :- set_prolog_flag(generate_debug_info, false). :- meta_predicate start_tabling(+, 0), current_table(:, -), abolish_table_subgoals(:). /** Tabled execution (SLG WAM) This library handled _tabled_ execution of predicates using the characteristics if the _SLG WAM_. The required suspension is is realised using _delimited continuations_ implemented by reset/3 and shift/1. The table space and work lists are part of the SWI-Prolog core. @author Benoit Desouter */ %! table(+PredicateIndicators) % % Prepare the given PredicateIndicators for tabling. Can only be % used as a directive. The example below prepares the predicate % edge/2 and the non-terminal statement//1 for tabled execution. % % == % :- table edge/2, statement//1. % == table(PIList) :- throw(error(context_error(nodirective, table(PIList)), _)). %! start_tabling(+Variant, +Implementation) % % Execute Implementation using tabling. This predicate should not % be called directly. The table/1 directive causes a predicate to % be translated into a renamed implementation and a wrapper that % involves this predicate. % % @compat This interface may change or disappear without notice % from future versions. start_tabling(Wrapper,Worker) :- '$tbl_variant_table'(Wrapper, Trie, Status), ( Status == complete -> trie_gen(Trie, Wrapper, _) ; ( '$tbl_scheduling_component'(false, true) -> catch(run_leader(Wrapper, Worker, Trie), E, true), ( var(E) -> trie_gen(Trie, Wrapper, _) ; '$tbl_table_discard_all', throw(E) ) ; run_follower(Status, Wrapper, Worker, Trie) ) ). run_follower(fresh, Wrapper, Worker, Trie) :- !, activate(Wrapper, Worker, Trie, Worklist), shift(call_info(Wrapper, Worklist)). run_follower(Worklist, Wrapper, _Worker, _Trie) :- shift(call_info(Wrapper, Worklist)). run_leader(Wrapper, Worker, Trie) :- activate(Wrapper, Worker, Trie, _Worklist), completion, '$tbl_scheduling_component'(_, false). activate(Wrapper, Worker, Trie, WorkList) :- '$tbl_new_worklist'(WorkList, Trie), ( delim(Wrapper, Worker, WorkList), fail ; true ). delim(Wrapper, Worker, WorkList) :- reset(Worker,SourceCall,Continuation), ( Continuation == 0 -> '$tbl_wkl_add_answer'(WorkList, Wrapper) ; SourceCall = call_info(SrcWrapper, SourceWL), TargetCall = call_info(Wrapper, WorkList), Dependency = dependency(SrcWrapper,Continuation,TargetCall), '$tbl_wkl_add_suspension'(SourceWL, Dependency) ). completion :- '$tbl_pop_worklist'(WorkList), !, completion_step(WorkList), completion. completion :- '$tbl_table_complete_all'. completion_step(SourceTable) :- ( '$tbl_wkl_work'(SourceTable, Answer, Dependency), dep(Answer, Dependency, Wrapper,Continuation,TargetTable), delim(Wrapper,Continuation,TargetTable), fail ; true ). dep(Answer, dependency(Answer, Continuation, call_info(Wrapper, TargetTable)), Wrapper, Continuation,TargetTable). /******************************* * CLEANUP * *******************************/ %! abolish_all_tables % % Remove all tables. This is normally used to free up the space or % recompute the result after predicates on which the result for % some tabled predicates depend. % % @error permission_error(abolish, table, all) if tabling is % in progress. abolish_all_tables :- '$tbl_abolish_all_tables'. %! abolish_table_subgoals(:Subgoal) is det. % % Abolish all tables that unify with SubGoal. abolish_table_subgoals(M:SubGoal) :- '$tbl_variant_table'(VariantTrie), current_module(M), forall(trie_gen(VariantTrie, M:SubGoal, Trie), '$tbl_destroy_table'(Trie)). /******************************* * EXAMINE TABLES * *******************************/ %! current_table(:Variant, -Trie) is nondet. % % True when Trie is the answer table for Variant. current_table(M:Variant, Trie) :- '$tbl_variant_table'(VariantTrie), ( (var(Variant) ; var(M)) -> trie_gen(VariantTrie, M:Variant, Trie) ; trie_lookup(VariantTrie, M:Variant, Trie) ). /******************************* * WRAPPER GENERATION * *******************************/ :- multifile system:term_expansion/2, prolog:rename_predicate/2, tabled/2. :- dynamic system:term_expansion/2. wrappers(Var) --> { var(Var), !, instantiation_error(Var) }. wrappers((A,B)) --> !, wrappers(A), wrappers(B). wrappers(Name//Arity) --> { atom(Name), integer(Arity), Arity >= 0, !, Arity1 is Arity+2 }, wrappers(Name/Arity1). wrappers(Name/Arity) --> { atom(Name), integer(Arity), Arity >= 0, !, functor(Head, Name, Arity), atom_concat(Name, ' tabled', WrapName), Head =.. [Name|Args], WrappedHead =.. [WrapName|Args], prolog_load_context(module, Module) }, [ '$tabled'(Head), ( Head :- start_tabling(Module:Head, WrappedHead) ) ]. %! prolog:rename_predicate(:Head0, :Head) is semidet. % % Hook into term_expansion for post processing renaming of the % generated predicate. prolog:rename_predicate(M:Head0, M:Head) :- '$flushed_predicate'(M:'$tabled'(_)), call(M:'$tabled'(Head0)), !, rename_term(Head0, Head). rename_term(Compound0, Compound) :- compound(Compound0), !, compound_name_arguments(Compound0, Name, Args), atom_concat(Name, ' tabled', WrapName), compound_name_arguments(Compound, WrapName, Args). rename_term(Name, WrapName) :- atom_concat(Name, ' tabled', WrapName). system:term_expansion((:- table(Preds)), [ (:- discontiguous('$tabled'/1)) | Clauses ]) :- phrase(wrappers(Preds), Clauses). /******************************* * SANDBOX * *******************************/ :- multifile sandbox:safe_directive/1, sandbox:safe_primitive/1, sandbox:safe_meta/2. %! sandbox:safe_directive(+Directive) is semidet. % % Allow tabling directives that affect locally defined predicates. sandbox:safe_directive(Dir) :- ground(Dir), local_tabling_dir(Dir). local_tabling_dir(table(Preds)) :- local_preds(Preds). local_preds((A,B)) :- !, local_preds(A), local_preds(B). local_preds(Name/Arity) :- atom(Name), integer(Arity). local_preds(Name//Arity) :- atom(Name), integer(Arity). sandbox:safe_meta_predicate(tabling:start_tabling/2). sandbox:safe_primitive(tabling:abolish_all_tables). sandbox:safe_meta(tabling:abolish_table_subgoals(V), []) :- \+ qualified(V). sandbox:safe_meta(tabling:current_table(V, _), []) :- \+ qualified(V). qualified(V) :- nonvar(V), V = _:_.