yap-6.3/swi/library/option.pl

/*  $Id$

    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
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    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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    You should have received a copy of the GNU Lesser General Public
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    As a special exception, if you link this library with other files,
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    library does not by itself cause the resulting executable to be covered
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*/

:- 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
@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).

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.

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).