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/* Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: J.Wielemaker@vu.nl
WWW: http://www.swi-prolog.org
Copyright (c) 2020, 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(intercept,
[ intercept/3, % :Goal, ?Ball, :Handler
intercept/4, % :Goal, ?Ball, :Handler, +Arg
intercept_all/4, % +Templ, :Goal, ?Ball, -List
nb_intercept_all/4, % +Templ, :Goal, ?Ball, -List
send_signal/1, % +Ball
send_silent_signal/1 % +Ball
]).
:- autoload(library(error),[must_be/2]).
/** <module> Intercept and signal interface
This library allows for creating an execution context (goal) which
defines how calls to send_signal/1 are handled. This library is
typically used to fetch values from the context or process results
depending on the context.
For example, assume we parse a (large) file using a grammar (see
phrase_from_file/3) that has some sort of _record_ structure. What
should we do with the recognised records? We can return them in a list,
but if the input is large this is a huge overhead if the records are to
be asserted or written to a file. Using this interface we can use
```
document -->
record(Record),
!,
{ send_signal(record(Record)) },
document.
document -->
[].
```
Given the above, we can assert all records into the database using the
following query:
```
...,
intercept(phrase_from_file(File, document),
record(Record),
assertz(Record)).
```
Or, we can collect all records in a list using intercept_all/4:
```
...,
intercept_all(Record,
phrase_from_file(File, document), record(Record),
Records).
```
*/
:- meta_predicate
intercept(0,?,0),
intercept(0,?,1,?),
intercept_all(?,0,?,-),
nb_intercept_all(?,0,?,-).
%! intercept(:Goal, ?Ball, :Handler)
%
% Run Goal as call/1. If somewhere during the execution of Goal
% send_signal/1 is called with a _Signal_ that unifies with Ball, run
% Handler and continue the execution.
%
% This predicate is related to catch/3, but rather than aborting the
% execution of Goal and running Handler it continues the execution of
% Goal. This construct is also related to _delimited continuations_
% (see reset/3 and shift/1). It only covers one (common) use case for
% delimited continuations, but does so with a simpler interface, at
% lower overhead and without suffering from poor interaction with the
% cut.
%
% Note that Ball and Handler are _copied_ before calling the (copy) of
% Handler to avoid instantiation of Ball and/or Handler which can make
% a subsequent signal fail.
%
% @see intercept/4, reset/3, catch/4, broadcast_request/1.
% @compat Ciao
intercept(Goal, Ball, Handler) :-
do_intercept(Goal, Ball, Handler, args).
%! intercept(:Goal, ?Ball, :Handler, +Arg)
%
% Similar to intercept/3, but the copy of Handler is called as
% call(Copy,Arg), which allows passing large context arguments or
% arguments subject to unification or _destructive assignment_. For
% example:
%
% ?- intercept(send_signal(x), X, Y=X).
% true.
%
% ?- intercept(send_signal(x), X, =(X), Y).
% Y = x.
intercept(Goal, Ball, Handler, Context) :-
do_intercept(Goal, Ball, Handler, args(Context)).
do_intercept(Goal, Ball, Handler, Context) :-
Goal,
no_lco(Ball, Handler, Context).
no_lco(_,_,_).
%! intercept_all(+Template, :Goal, ?Ball, -List).
%
% True when List contains all instances of Template that have been
% sent using send_signal/1 where the argument unifies with Ball. Note
% that backtracking in Goal resets the List. For example, given
%
% ```
% enum(I, Max) :- I =< Max, !, send_signal(emit(I)),
% I2 is I+1, enum(I2, Max).
% enum(_, _).
% ```
%
% Consider the following queries
%
% ?- intercept_all(I, enum(1,6), emit(I), List).
% List = [1, 2, 3, 4, 5, 6].
%
% ?- intercept_all(I, (between(1,3,Max),enum(1,Max)),
% emit(I), List).
% Max = 1, List = [1] ;
% Max = 2, List = [1, 2] ;
% Max = 3, List = [1, 2, 3].
%
% @see nb_intercept_all/4
intercept_all(Template, Goal, Ball, List) :-
List0 = [_],
State = list(List0, List0),
intercept(Goal, Ball, add_ball(Template), State),
arg(1, State, [_|List]).
add_ball(Elem, State) :-
Tail = [Elem],
arg(2, State, List),
setarg(2, List, Tail),
setarg(2, State, Tail).
%! nb_intercept_all(+Template, :Goal, ?Ball, -List)
%
% As intercept_all/4, but backtracing inside Goal does not reset List.
% Consider this program and the subsequent queries
%
% ```
% enum_b(F, T) :- forall(between(F, T, I), send_signal(emit(I))).
% ```
%
% ?- intercept_all(I, enum_b(1, 6), emit(I), List).
% List = [].
%
% ?- nb_intercept_all(I, enum_b(1, 6), emit(I), List).
% List = [1, 2, 3, 4, 5, 6].
nb_intercept_all(Template, Goal, Ball, List) :-
List0 = [_],
State = list(List0, List0),
intercept(Goal, Ball, nb_add_ball(Template), State),
arg(1, State, [_|List]).
nb_add_ball(Elem, State) :-
duplicate_term(Elem, Copy),
Tail = [Copy],
arg(2, State, List),
nb_linkarg(2, List, Tail),
nb_linkarg(2, State, Tail).
%! send_signal(+Signal)
%
% If this predicate is called from a sub-goal of intercept/3, execute
% the associated _Handler_ of the intercept/3 environment.
%
% @error unintercepted_signal(Signal) if there is no matching
% intercept environment.
send_signal(Signal) :-
must_be(nonvar, Signal),
prolog_current_frame(Frame),
( interceptor(Frame, Signal, Handler, Context)
-> call_handler(Context, Handler)
; throw(error(unintercepted_signal(Signal), _))
).
%! send_silent_signal(+Signal)
%
% As send_signal/1, but succeed silently if there is no matching
% intercept environment.
send_silent_signal(Signal) :-
must_be(nonvar, Signal),
prolog_current_frame(Frame),
( interceptor(Frame, Signal, Handler, Context)
-> call_handler(Context, Handler)
; true
).
call_handler(args, Handler) :-
call(Handler).
call_handler(args(A0), Handler) :-
call(Handler, A0).
interceptor(Frame, Signal, Handler, Context) :-
prolog_frame_attribute(Frame, parent_goal(Next),
intercept:do_intercept(_Goal, Signal0, Handler0, Context)),
( copy_term(Signal0+Handler0, Signal+Handler)
-> true
; interceptor(Next, Signal, Handler, Context)
).
/*******************************
* SANDBOX *
*******************************/
:- multifile
sandbox:safe_meta_predicate/1,
sandbox:safe_primitive/1.
sandbox:safe_meta_predicate(intercept:intercept/3).
sandbox:safe_meta_predicate(intercept:intercept/4).
sandbox:safe_meta_predicate(intercept:intercept_all/4).
sandbox:safe_meta_predicate(intercept:nb_intercept_all/4).
sandbox:safe_primitive(intercept:send_signal(_)).
sandbox:safe_primitive(intercept:send_silent_signal(_)).
|
