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tabling.pl -- Tabled execution (SLG WAM)
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This library handled tabled execution of predicates using the characteristics if the SLG WAM. The required suspension 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, Jan Wielemaker and Fabrizio Riguzzi
Source table :PredicateIndicators
Prepare the given PredicateIndicators for tabling. This predicate is normally used as a directive, but SWI-Prolog also allows runtime conversion of non-tabled predicates to tabled predicates by calling table/1. The example below prepares the predicate edge/2 and the non-terminal statement//1 for tabled execution.
:- table edge/2, statement//1.

In addition to using predicate indicators, a predicate can be declared for mode directed tabling using a term where each argument declares the intended mode. For example:

:- table connection(_,_,min).

Mode directed tabling is discussed in the general introduction section about tabling.

Source untable(M:PIList) is det
Remove tabling for the predicates in PIList. This can be used to undo the effect of table/1 at runtime. In addition to removing the tabling instrumentation this also removes possibly associated tables using abolish_table_subgoals/1.
Arguments:
PIList- is a comma-list that is compatible ith table/1.
Source start_tabling(:Closure, :Wrapper, :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.
Arguments:
Closure- is the wrapper closure to find the predicate quickly. It is also allowed to pass nothing. In that cases the predicate is looked up using Wrapper. We suggest to pass 0 in this case.
Compatibility
- This interface may change or disappear without notice from future versions.
Source start_subsumptive_tabling(:Closure, :Wrapper, :Implementation)
(*) We should not use trie_gen_compiled/2 here as this will enumerate all answers while '$tbl_answer_update_dl'/2 uses the available trie indexing to only fetch the relevant answer(s).
To be done
- In the end '$tbl_answer_update_dl'/2 is problematic with incremental and shared tabling as we do not get the consistent update view from the compiled result.
Source start_abstract_tabling(:Closure, :Wrapper, :Worker)
Deal with table p/1 as subgoal_abstract(N). This is a merge between variant and subsumptive tabling. If the goal is not abstracted this is simple variant tabling. If the goal is abstracted we must solve the more general goal and use answers from the abstract table.

Wrapper is e.g., user:p(s(s(s(X))),Y) Worker is e.g., call(<closure>(p/2)(s(s(s(X))),Y))

Source start_moded_tabling(+Closure, :Wrapper, :Implementation, +Variant, +ModeArgs)
As start_tabling/2, but in addition separates the data stored in the answer trie in the Variant and ModeArgs.
Source update(+Flags, +Head, +Module, +A1, +A2, -A3, -Action) is semidet
Update the aggregated value for an answer. Iff this predicate succeeds, the aggregated value is updated to A3. If Del is unified with true, A1 should be deleted.
Arguments:
Flags- is a bit mask telling which of A1 and A2 are uncondional
Head- is the head of the predicate
Module- is the module of the predicate
A1- is the currently aggregated value
A2- is the newly produced value
Action- is one of
  • delete to replace the old answer with the new
  • keep to keep the old answer and add the new
  • done to stop the update process
Source tnot(:Goal)
Tabled negation.

(*): Only variant tabling is allowed under tnot/1.

Source not_exists(:P) is semidet
Tabled negation for non-ground goals. This predicate uses the tabled meta-predicate tabled_call/1. The tables for tabled_call/1 must be cleared if `the world changes' as well as to avoid aggregating too many variants.
Source $wfs_call(:Goal, :Delays)
Call Goal and provide WFS delayed goals as a conjunction in Delays. This predicate is the internal version of call_delays/2 from library(wfs).
Source 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.

Abolishes both local and shared tables. Possibly incomplete tables are marked for destruction upon completion. The dependency graphs for incremental and monotonic tabling are reclaimed as well.

Source abolish_table_subgoals(:Subgoal) is det
Abolish all tables that unify with SubGoal.
To be done
- : SubGoal must be callable. Should we allow for more general patterns?
Source abolish_module_tables(+Module) is det
Abolish all tables for predicates associated with the given module.
Source abolish_nonincremental_tables is det
Abolish all tables that are not related to incremental predicates.
Source abolish_nonincremental_tables(+Options)
Allow for skipping incomplete tables while abolishing.
To be done
- Mark tables for destruction such that they are abolished when completed.
Source current_table(:Variant, -Trie) is nondet
True when Trie is the answer table for Variant. If Variant has an unbound module or goal, all possible answer tries are generated, otherwise Variant is considered a fully instantiated variant and the predicate is semidet.
Source first(+S0, +S1, -S) is det
Source last(+S0, +S1, -S) is det
Source min(+S0, +S1, -S) is det
Source max(+S0, +S1, -S) is det
Source sum(+S0, +S1, -S) is det
Implement YAP tabling modes.
Source $set_table_wrappers(:Head)
Clear/add wrappers and notifications to trap dynamic predicates. This is required both for incremental and monotonic tabling.
Source $start_monotonic(+Head, +Wrapped)
This is called the monotonic wrapper around a dynamic predicate to collect the dependencies between the dynamic predicate and the monotonic tabled predicates.
Source monotonic_update(+Action, +ClauseRef)
Trap changes to the monotonic dynamic predicate and forward them.
Source abolish_monotonic_tables
Abolish all monotonic tables and the monotonic dependency relations.
To be done
- : just prepare for incremental reevaluation?
Source dyn_update(+Action, +Context) is det
Track changes to added or removed clauses. We use '$clause'/4 because it works on erased clauses.
To be done
- Add a '$clause_head'(-Head, +ClauseRef) to only decompile the head.
Source answer_completion(+AnswerTrie, +Return) is det
Find positive loops in the residual program and remove the corresponding answers, possibly causing additional simplification. This is called from C if simplify_component() detects there are conditional answers after simplification.

Note that we are called recursively from C. Our caller prepared a clean new tabling environment and restores the old one after this predicate terminates.

author
- This code is by David Warren as part of XSB.
See also
- called from C, pl-tabling.c, answer_completion()
Source tripwire(+Wire, +Action, +Context)
Called from the tabling engine of some tripwire is exceeded and the situation is not handled internally (such as abstract and bounded_rationality.
 undefined is undefined
Expresses the value bottom from the well founded semantics.
 answer_count_restraint is undefined
 radial_restraint is undefined
Similar to undefined/0, providing a specific undefined for restraint violations.

Undocumented predicates

The following predicates are exported, but not or incorrectly documented.

 radial_restraint
Source abolish_shared_tables
Source $wrap_tabled(Arg1, Arg2)
Source $tbl_answer(Arg1, Arg2, Arg3, Arg4)
Source $moded_wrap_tabled(Arg1, Arg2, Arg3, Arg4, Arg5)
Source abolish_private_tables