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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) 2018, VU University Amsterdam
CWI, 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(dcg_high_order,
[ sequence//2, % :Element, ?List
sequence//3, % :Element, :Sep, ?List
sequence//5, % :Start, :Element, :Sep, :End, ?List
optional//2, % :Match, :Otherwise
foreach//2, % :Generator, :Element
foreach//3 % :Generator, :Element, :Sep
]).
:- use_module(library(ordsets)).
:- meta_predicate
sequence(3,?,?,?),
sequence(3,//,?,?,?),
sequence(//,3,//,//,?,?,?),
optional(//, //, ?, ?),
foreach(0,//,?,?),
foreach(0,//,//,?,?).
/** <module> High order grammar operations
This library provides facilities comparable maplist/3, ignore/1 and
foreach/2 for DCGs.
__STATUS__: This library is experimental. The interface and
implementation may change based on feedback. Please send feedback to the
mailinglist or the issue page of the `swipl-devel.git` repository.
*/
%! sequence(:Element, ?List)// is nondet.
%
% Match or generate a sequence of Element. This predicate is
% deterministic if List is fully instantiated and Element is
% deterministic. When parsing, this predicate is _gready_ and does not
% prune choice points. For example:
%
% ?- phrase(sequence(digit, Digits), `123a`, L).
% Digits = "123",
% L = [97] ;
% Digits = [49, 50],
% L = [51, 97] ;
% ...
sequence(OnElem, List) -->
sequence_(List, OnElem).
sequence_([H|T], P) -->
call(P, H),
sequence_(T, P).
sequence_([], _) -->
[].
%! sequence(:Element, :Sep, ?List)// is nondet.
%
% Match or generate a sequence of Element where each pair of elements
% is separated by Sep. When _parsing_, a matched Sep _commits_. The
% final element is _not_ committed. See also sequence//5.
sequence(OnElem, OnSep, List) -->
sequence_(List, OnElem, OnSep).
%! sequence(:Start, :Element, :Sep, :End, ?List)// is semidet.
%
% Match or generate a sequence of Element enclosed by Start end End,
% where each pair of elements is separated by Sep. More formally, it
% matches the following sequence:
%
% Start (Element,Sep)*, End
%
% The example below matches a Prolog list of integers:
%
% ?- phrase(sequence(("[",blanks),
% number, (",",blanks),
% (blanks,"]"), L),
% `[1, 2, 3 ] a`, Tail).
% L = [1, 2, 3],
% Tail = [32, 97].
sequence(Start, OnElem, OnSep, End, List) -->
Start,
sequence_(List, OnElem, OnSep),
End, !.
sequence_([H|T], P, Sep) -->
call(P, H),
( {T == []}
-> []
; Sep
-> !, sequence_(T, P, Sep)
; {T = []}
).
sequence_([], _, _) -->
[].
%! optional(:Match, :Default)// is det.
%
% Perform an optional match, executing Default if Match is not
% matched. This is comparable to ignore/1. Both Match and Default are
% DCG body terms. Default is typically used to instantiate the output
% variables of Match, but may also be used to match a default
% representation. Using `[]` for Default succeeds without any
% additional actions if Match fails. For example:
%
% ?- phrase(optional(number(X), {X=0}), `23`, Tail).
% X = 23,
% Tail = [].
% ?- phrase(optional(number(X), {X=0}), `aap`, Tail).
% X = 0,
% Tail = `aap`.
optional(Match, _Default) -->
Match, !.
optional(_, Default) -->
Default, !.
%! foreach(:Generator, :Element)// is det.
%! foreach(:Generator, :Element, :Sep)// is det.
%
% Generate a list from the solutions of Generator. This predicate
% collects all solutions of Generator, applies Element for each
% solution and Sep _between_ each pair of solutions. For example:
%
% ?- phrase(foreach(between(1,5,X), number(X), ", "), L).
% L = "1, 2, 3, 4, 5, 6, 7, 8, 9, 10".
foreach(Generator, Rule) -->
foreach(Generator, Rule, []).
foreach(Generator, Rule, Sep) -->
{ term_variables(Generator, GenVars0), sort(GenVars0, GenVars),
term_variables((Rule,Sep), GoalVars0), sort(GoalVars0, GoalVars),
ord_subtract(GoalVars, GenVars, SharedGoalVars),
ord_intersection(GenVars, GoalVars, SharedVars),
Templ =.. [v|SharedVars],
SharedTempl =.. [v|SharedGoalVars],
findall(Templ, Generator, List)
},
emit_list(List, Templ, SharedTempl, Rule, Sep).
emit_list([], _, _, _, _) -->
[].
emit_list([H|T], Templ, SharedTempl, OnElem, OnSep) -->
{ copy_term(t(Templ,SharedTempl,OnElem,OnSep),
t(H,SharedTempl,OnElemCopy,OnSepCopy))
},
OnElemCopy,
( { T == [] }
-> []
; OnSepCopy,
emit_list(T, Templ, SharedTempl, OnElem, OnSep)
).
/*******************************
* SANDBOX *
*******************************/
:- multifile sandbox:safe_meta_predicate/1.
sandbox:safe_meta_predicate(dcg_high_order:sequence/4).
sandbox:safe_meta_predicate(dcg_high_order:sequence/5).
sandbox:safe_meta_predicate(dcg_high_order:sequence/7).
sandbox:safe_meta_predicate(dcg_high_order:optional/4).
sandbox:safe_meta_predicate(dcg_high_order:foreach/4).
sandbox:safe_meta_predicate(dcg_high_order:foreach/5).
|
