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yap-6.3/swi/library/option.pl

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/* $Id$
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)).
/** <module> Option list processing
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@ingroup swi
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_<record>/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).
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option(Opt, Options) :- % make option processing stead-fast
atom(Opt),
!,
get_option(Opt, Options).
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.
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select_option(Opt, Options0, Options) :- % stead-fast
atom(Opt),
!,
select_option(Opt, Options0, Options).
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).