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documentation for tabling execution.

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@ -6535,6 +6535,10 @@ Yap. Currently it informs whether the system supports
@code{or-parallelism}, @code{rational_trees}, @code{tabling},
@code{threads}, or the @code{wam_profiler}.
@item tabling_mode
@* Sets or reads the tabling mode for all tabled predicates. Please
@pxref{Tabling} for the list of options.
@item to_chars_mode
@findex to_chars_modes (yap_flag/2 option)
@* Define whether YAP should follow @code{quintus}-like
@ -10509,59 +10513,154 @@ releases.
@node Tabling, Low Level Tracing, Parallelism , Extensions
@chapter Tabling
@cindex tabling
An initial cut for an implementation of tabling in the style of
XSB-Prolog is now available. Tabling was implemented by Ricardo
Rocha. To experiment with tabling use @code{-DTABLING} to
@code{YAP_EXTRAS} in the system's @code{Makefile}.
You can use the directive @code{table} to force calls for the argument
predicate to be tabled. Tabling information is stored in a trie, as for
XSB-Prolog.
@strong{YapTab} is the tabling engine that extends Yap's execution
model to support tabled evaluation for definite programs. YapTab was
implemented by Ricardo Rocha and its implementation is largely based
on the ground-breaking design of the XSB Prolog system, which
implements the SLG-WAM. Tables are implemented using tries and YapTab
supports the dynamic intermixing of batched scheduling and local
scheduling at the subgoal level. Currently, the following restrictions
are of note:
@itemize @bullet
@item YapTab does not handle tabled predicates with loops through negation (undefined behaviour).
@item YapTab does not handle tabled predicates with cuts (undefined behaviour).
@item YapTab does not support coroutining (configure error).
@item YapTab does not support tabling dynamic predicates (permission error).
@end itemize
To experiment with YapTab use @code{--enable-tabling} in the configure
script or add @code{-DTABLING} to @code{YAP_EXTRAS} in the system's
@code{Makefile}. We next describe the set of built-ins predicates
designed to interact with YapTab and control tabled execution:
The following predicates may be useful to control tabled execution:
@table @code
@item is_tabled(+@var{PredIndicator})
@item table +@var{P}
@findex table/1
@snindex table/1
@cnindex table/1
Declares predicate @var{P} (or a list of predicates
@var{P1},...,@var{Pn} or [@var{P1},...,@var{Pn}]) as a tabled
predicate. @var{P} must be written in the form
@var{name/arity}. Examples:
@example
:- table son/3.
:- table father/2.
:- table mother/2.
@end example
@noindent or
@example
:- table son/3, father/2, mother/2.
@end example
@noindent or
@example
:- table [son/3, father/2, mother/2].
@end example
@item is_tabled(+@var{P})
@findex is_tabled/1
@snindex is_tabled/1
@cnindex is_tabled/1
Succeeds if the predicate @var{PredIndicator}, of the form
@var{Name/Arity}, is a tabled predicate.
Succeeds if the predicate @var{P} (or a list of predicates
@var{P1},...,@var{Pn} or [@var{P1},...,@var{Pn}]), of the form
@var{name/arity}, is a tabled predicate.
@item tabling_mode(+@var{PredIndicator},+@var{Options})
@findex is_tabled/1
@snindex is_tabled/1
@cnindex is_tabled/1
Sets tabling mode options for the list or predicate given by
@var{PredIndicator}. The list of @var{Options} includes:
@item tabling_mode(+@var{P},?@var{Mode})
@findex tabling_mode/2
@snindex tabling_mode/2
@cnindex tabling_mode/2
Sets or reads the default tabling mode for a tabled predicate @var{P}
(or a list of predicates @var{P1},...,@var{Pn} or
[@var{P1},...,@var{Pn}]). The list of @var{Mode} options includes:
@table @code
@item @code{batched}: use batched scheduling for this predicate (default).
@item @code{local}: use local scheduling for this predicate.
@item @code{exec_answers}: use complete tries as code (default).
@item @code{load_answers}: use complete tries as a consumer, somewhat less
efficient but creates less choice-points.
@item batched
Defines that, by default, batched scheduling is the scheduling
strategy to be used to evaluated calls to predicate @var{P}.
@item local
Defines that, by default, local scheduling is the scheduling
strategy to be used to evaluated calls to predicate @var{P}.
@item exec_answers
Defines that, by default, when a call to predicate @var{P} is
already evaluated (completed), answers are obtained by executing
compiled WAM-like code directly from the trie data
structure. This reduces the loading time when backtracking, but
the order in which answers are obtained is undefined.
@item load_answers
Defines that, by default, when a call to predicate @var{P} is
already evaluated (completed), answers are obtained (as a
consumer) by loading them from the trie data structure. This
guarantees that answers are obtained in the same order as they
were found. Somewhat less efficient but creates less choice-points.
@end table
The default tabling mode for a new tabled predicate is @code{batched}
and @code{exec_answers}. To set the tabling mode for all predicates at
once you can use the @code{yap_flag/2} predicate as described next.
@item yap_flag(tabling_mode,?@var{Mode})
@findex tabling_mode (yap_flag/2 option)
Sets or reads the tabling mode for all tabled predicates. The list of
@var{Mode} options includes:
@table @code
@item default
Defines that (i) all calls to tabled predicates are evaluated
using the predicate default mode, and that (ii) answers for all
completed calls are obtained by using the predicate default mode.
@item batched
Defines that all calls to tabled predicates are evaluated using
batched scheduling. This option ignores the default tabling mode
of each predicate.
@item local
Defines that all calls to tabled predicates are evaluated using
local scheduling. This option ignores the default tabling mode
of each predicate.
@item exec_answers
Defines that answers for all completed calls are obtained by
executing compiled WAM-like code directly from the trie data
structure. This option ignores the default tabling mode
of each predicate.
@item load_answers
Defines that answers for all completed calls are obtained by
loading them from the trie data structure. This option ignores
the default tabling mode of each predicate.
@end table
@item abolish_table(+@var{PredIndicator})
@item abolish_table(+@var{P})
@findex abolish_table/1
@snindex abolish_table/1
@cnindex abolish_table/1
Remove tables for @var{PredIndicator}
Removes all the entries from the table space for predicate @var{P} (or
a list of predicates @var{P1},...,@var{Pn} or
[@var{P1},...,@var{Pn}]). The predicate remains as a tabled predicate.
@item show_table(+@var{PredIndicator})
@item abolish_all_tables/0
@findex abolish_all_tables/0
@snindex abolish_all_tables/0
@cnindex abolish_all_tables/0
Removes all the entries from the table space for all tabled
predicates. The predicates remain as tabled predicates.
@item show_table(+@var{P})
@findex show_table/1
@snindex show_table/1
@cnindex show_table/1
Print out the contents of the table generated for @var{PredIndicator}.
Prints table contents (subgoals and answers) for predicate @var{P}
(or a list of predicates @var{P1},...,@var{Pn} or
[@var{P1},...,@var{Pn}]).
@item table_statistics(+@var{PredIndicator})
@item table_statistics(+@var{P})
@findex table_statistics/1
@snindex table_statistics/1
@cnindex table_statistics/1
Print out some information on the current tables for
@var{PredIndicator}.
Prints table statistics (subgoals and answers) for predicate @var{P}
(or a list of predicates @var{P1},...,@var{Pn} or
[@var{P1},...,@var{Pn}]).
@item tabling_statistics/0
@findex tabling_statistics/0
@snindex tabling_statistics/0
@cnindex tabling_statistics/0
Prints statistics on space used by all tables.
@end table