/* $Id$ Part of SWI-Prolog Author: Jan Wielemaker E-mail: J.Wielemaker@uva.nl WWW: http://www.swi-prolog.org Copyright (C): 1985-2009, University of Amsterdam This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA As a special exception, if you link this library with other files, compiled with a Free Software compiler, to produce an executable, this library does not by itself cause the resulting executable to be covered by the GNU General Public License. This exception does not however invalidate any other reasons why the executable file might be covered by the GNU General Public License. */ :- module(swi_option, [ option/2, % +Term, +List option/3, % +Term, +List, +Default select_option/3, % +Term, +Options, -RestOpts select_option/4, % +Term, +Options, -RestOpts, +Default merge_options/3, % +New, +Old, -Merged meta_options/3 % :IsMeta, :OptionsIn, -OptionsOut ]). :- use_module(library(lists)). /** Option list processing The library(option) provides some utilities for processing option lists. Option lists are commonly used as an alternative for many arguments. Examples built-in predicates are open/4 and write_term/3. Naming the arguments results in more readable code and the list nature makes it easy to extend the list of options accepted by a predicate. Option lists come in two styles, both of which are handled by this library. $ Name(Value) : This is the preferred style. $ Name = Value : This is often used, but deprecated. Processing options inside time critical code (loops) can cause serious overhead. One possibility is to define a record using library(record) and initialise this using make_/2. In addition to providing good performance, this also provides type-checking and central declaration of defaults. == :- record atts(width:integer=100, shape:oneof([box,circle])=box). process(Data, Options) :- make_atts(Options, Attributes), action(Data, Attributes). action(Data, Attributes) :- atts_shape(Attributes, Shape), ... == @tbd We should consider putting many options in an assoc or record with appropriate preprocessing to achieve better performance. @tbd We should provide some standard to to automatic type-checking on option lists. @see library(record) */ %% option(?Option, +OptionList, +Default) % % Get an option from a OptionList. OptionList can use the % Name=Value as well as the Name(Value) convention. % % @param Option Term of the form Name(?Value). option(Opt, Options, Default) :- % make option processing stead-fast arg(1, Opt, OptVal), ground(OptVal), !, functor(Opt, OptName, 1), functor(Gen, OptName, 1), option(Gen, Options, Default), Opt = Gen. option(Opt, Options, _) :- get_option(Opt, Options), !. option(Opt, _, Default) :- arg(1, Opt, Default). %% option(?Option, +OptionList) % % Get an option from a OptionList. OptionList can use the % Name=Value as well as the Name(Value) convention. Fails silently % if the option does not appear in OptionList. % % @param Option Term of the form Name(?Value). option(Opt, Options) :- % make option processing stead-fast arg(1, Opt, OptVal), nonvar(OptVal), !, functor(Opt, OptName, 1), functor(Gen, OptName, 1), option(Gen, Options), Opt = Gen. option(Opt, Options) :- get_option(Opt, Options), !. get_option(Opt, Options) :- memberchk(Opt, Options), !. get_option(Opt, Options) :- functor(Opt, OptName, 1), arg(1, Opt, OptVal), memberchk(OptName=OptVal, Options), !. %% select_option(?Option, +Options, -RestOptions) is semidet. % % Get and remove option from an option list. As option/2, removing % the matching option from Options and unifying the remaining % options with RestOptions. select_option(Opt, Options0, Options) :- % stead-fast arg(1, Opt, OptVal), nonvar(OptVal), !, functor(Opt, OptName, 1), functor(Gen, OptName, 1), select_option(Gen, Options0, Options), Opt = Gen. select_option(Opt, Options0, Options) :- get_option(Opt, Options0, Options), !. get_option(Opt, Options0, Options) :- select(Opt, Options0, Options), !. get_option(Opt, Options0, Options) :- functor(Opt, OptName, 1), arg(1, Opt, OptVal), select(OptName=OptVal, Options0, Options), !. %% select_option(?Option, +Options, -RestOptions, +Default) is det. % % Get and remove option with default value. As select_option/3, % but if Option is not in Options, its value is unified with % Default and RestOptions with Options. select_option(Option, Options, RestOptions, _Default) :- select_option(Option, Options, RestOptions), !. select_option(Option, Options, Options, Default) :- arg(1, Option, Default). %% merge_options(+New, +Old, -Merged) is det. % % Merge two option lists. Merged is a sorted list of options using % the canonical format Name(Value) holding all options from New % and Old, after removing conflicting options from Old. merge_options([], Old, Merged) :- !, Merged = Old. merge_options(New, [], Merged) :- !, Merged = New. merge_options(New, Old, Merged) :- canonise_options(New, NCanonical), canonise_options(Old, OCanonical), sort(NCanonical, NSorted), sort(OCanonical, OSorted), ord_merge(NSorted, OSorted, Merged). ord_merge([], L, L) :- !. ord_merge(L, [], L) :- !. ord_merge([NO|TN], [OO|TO], Merged) :- functor(NO, NName, 1), functor(OO, OName, 1), compare(Diff, NName, OName), ord_merge(Diff, NO, NName, OO, OName, TN, TO, Merged). ord_merge(=, NO, _, _, _, TN, TO, [NO|T]) :- ord_merge(TN, TO, T). ord_merge(<, NO, _, OO, OName, TN, TO, [NO|T]) :- ( TN = [H|TN2] -> functor(H, NName, 1), compare(Diff, NName, OName), ord_merge(Diff, H, NName, OO, OName, TN2, TO, T) ; T = [OO|TO] ). ord_merge(>, NO, NName, OO, _, TN, TO, [OO|T]) :- ( TO = [H|TO2] -> functor(H, OName, 1), compare(Diff, NName, OName), ord_merge(Diff, NO, NName, H, OName, TN, TO2, T) ; T = [NO|TN] ). %% canonise_options(+OptionsIn, -OptionsOut) is det. % % Rewrite option list from possible Name=Value to Name(Value) canonise_options(In, Out) :- memberchk(_=_, In), !, % speedup a bit if already ok. canonise_options2(In, Out). canonise_options(Options, Options). canonise_options2([], []). canonise_options2([Name=Value|T0], [H|T]) :- !, H =.. [Name,Value], canonise_options2(T0, T). canonise_options2([H|T0], [H|T]) :- !, canonise_options2(T0, T). %% meta_options(+IsMeta, :Options0, -Options) is det. % % Perform meta-expansion on options that are module-sensitive. % Whether an option name is module sensitive is determined by % calling call(IsMeta, Name). Here is an example: % % == % meta_options(is_meta, OptionsIn, Options), % ... % % is_meta(callback). % == :- meta_predicate meta_options(1, :, -). meta_options(IsMeta, Context:Options0, Options) :- meta_options(Options0, IsMeta, Context, Options). meta_options([], _, _, []). meta_options([H0|T0], IM, Context, [H|T]) :- meta_option(H0, IM, Context, H), meta_options(T0, IM, Context, T). meta_option(Name=V0, IM, Context, Name=M:V) :- call(IM, Name), !, strip_module(Context:V0, M, V). meta_option(O0, IM, Context, O) :- compound(O0), O0 =.. [Name,V0], call(IM, Name), !, strip_module(Context:V0, M, V), O =.. [Name,M:V]. meta_option(O, _, _, O).