options.pl -- Options handling and processing.

This is a stoics.infrastructure pack for handling option arguments. The main concept is to treat options as naive Prolog lists which the programmer can manipulate and specialise if they need to, while providing a small number of predicates that manage basic common operations on options. Options are particularly important in the context of SWI packs, as making code publicly available to others often involves allowing for variations in the behaviour of the code.

The library provides simple extensions to the basic list manipulation predicates. In many cases it is just the error handling that is the main difference to standard predicates.

Technically the library is designed on the semantics of memberchk/2. Looking for an Option in a list of options, memberchk/2 will return the leftmost match. Library(options) sees options as a concatenation (append/3) of the user provided options (arguments for hereon) and the defaults provided by the predicate.

The default option values for a predicate are given by a predicate of the same name but postfixed by '_defaults'. The library also allows for reading user specific default options by reading profiles from a file located at $HOME/.pl/<pred_name>.pl, if that file exists. Each options file should have a number of option terms given as facts.

Some distinctive features of pack(options)

For an example see program options_example_sort_defaults.pl in examples directory.

?- edit( pack(options/examples/ex_sort) ).

?- [pack(options/examples/ex_sort)].

?- ex_sort( [a,b,e,c,b], Ord, true ).
Ord = [a, b, c, e].
?- ex_sort( [a,b,e,c,b], Ord, debug(true) ).
% Input list length: 5
% Output list length: 4
Ord = [a, b, c, e].
?- ex_sort( [a,b,e,c,b], Ord, order(>) ).
Ord = [e, c, b, a].
?- ex_sort( [a,b,e,c,b], Ord, duplicates(true) ).
Ord = [a, b, b, c, e].

Create file $HOME/.pl/ex_sort.pl with content order(>).

?- ex_sort( [a,b,e,c,b], Ord, true ).
Ord = [e, c, b, a].

Default for user is now order(>) which can still be over-ridden at invocation

?- ex_sort( [a,b,e,c,b], Ord, order(<) ).
Ord = [a, b, c, e].

Pack info


Thanks to Jan Wielemaker for fixing an issue with expanding the $HOME variable and missing curly brackets in the errors DCG (2016/11/14).

- nicos angelopoulos
- 0.2.0 2015/7/5
- 0.4.0 2016/2/29
- 0.5.0 2017/3/10
- 1.0 2018/3/18
- 1.1 2018/4/8
See also
- http://www.stoics.org.uk/~nicos/sware/options
 options_append(+PredName, +OptS, -All)
 options_append(+PredName, +OptS, -All, +OAopts)
Look for PredName_defaults/1 and if that exists append its argumetn to the end of OptS to get All.
OptS is casted to a list before the append, so single terms are allowed as options.
In addition, if file user_profile('.pl'/Pname) exists, its terms are appended between OptS and the argument of PredName_defaults/1.
Appending of the profile terms, can be by passed with options append_profile(false).
Listens to debug(options_append).

The predicate can process debug(Dbg) a commonly used option (in All). When Dbg is set to true debug( PredName ) is called.
The default value of Dbg is provided by PredName_defaults/1.

OptS and All are options of PredName, whereas OAopts are options of options_append/4 and control how OptS are transformed into All.

OAopts term or list of

args(Opts=en_list(OptS, Opts))
the input OptS, but guaranteed to be a list
if false do not append the profile options
the arity of the caller, only used for reporting type errors for now
removes atoms from input arguments, and instantiates them into Atoms. OptS == true, is an exception: Atoms is instantiated to []
if the defaults predicate returns a default of options_types(OTypes), this is removed and used to check the types of the supplied options. OTypes should be OptName-Type pairs list with Type being one of those recognised by type/2 in pack(pack_errors).
multiple allowed. All Arg(s) so passed are added to the Args passed to the defaults predicate, but not to the generated options. Allows for instance to pass arguments of the call itself to the defaults predicate without those arguments being added to the Options list
instantiates to all input options that do not have matching default term structure
if true debug this call, and call prolog_debug:debug_topic(Pname). if false trun debugging off for this call. Else Dbg can be a debug term (other than none,false,true) or list of debug terms.
as process() below, but leaves processed options in All.
caller pack. For now it is only used to report type errors
with Proccess in
will turn on debugging according to debug/0,1,2 options, see below
to pass options_types(OTypes) to the result Options use Rtypes == false

When processing debugging options in All, the first matching term of the following is used:

?- assert( demo_defaults(ls(true)) ).
?- options_append( demo, ls(false), All ).
All = [ls(false), ls(true)].
?- options_append( demo, debug, All, process(debug) ).
All = [ls(true)].
?- options_append( demo, [debug(true),ls(false)], All, [process(debug),debug(true)] ).
Turning debugging on for predicate handle: demo
All = [ls(false), ls(true)].
% Note that the debug(options_append) has been removed in the following:
?- options_append( demo, debug, All, process(debug) ).
All = [ls(true)].

?- [pack(options/examples/ex_app)].
?- ex_app.

The default OAopts list is [funnel(debug)].

- nicos angelopoulos
- 0.2 2014/9/20
See also
- ~/bin/cline/keep.pl for debug option example
- pack(options/examples/ex_app.pl)
To be done
- add option! for making sure that only recognised options (with additional,"silent" defaults) are accepted ??
- allow for strict lists inputs
 options_debug(+Format, +Args, +Opts)
Call debug(_,Format,Args) iff debug(true) is the first debug(_) term in list Opts
 ?- options_debug( 'A simple message at: ~w', noon, [debug(true)] ).
 ?- options_debug( 'A simple message at: ~w', noon, [] ).
- nicos angelopoulos
- 0.1 2015/1/15
 options_propagate(+Onames, +OptsIn, -OptsOut, +PropOpts)
Propagate all options with names in Onames from OptsIn to OptsOut. Onames can be a single un_listed option name (en_list/2).

The predicate does not check arities.

The order in OptsOut follows the order in Onames.

PropOpts control the predicate behaviour

duplicates are removed, use match(all) for no removal
- nicos angelopoulos
- 0.1 2015/3/19
To be done
- type checking of Match via options_append/4.
 options_restore(+Self, +Opts)
Restore all options_append/3, auto processed options.

This predicate is often called at the end of a deterministic call that depends on a set of options.

Currently the only option that is restored is

Internals; The predicate looks for any macthing '$restore'(Self,OptName,Status), so it should be extensible to other state-based options processing.

 options_return(+TermS, +OptS)
The predicate always succeeds. In addition, if memberchk( Term, OptS ) succeeds of single Term in the possibly listed term list TermS, then any unbound parts of TermS maybe become more ground.

This predicate can be used to instantiate return options.

OptS and TermS are passed through en_list/2.

 ?- options_return( cnm(Cnm), [abc(x),cnm(symbols)] ).
 Cnm = symbols.
 ?- options_return( [data(Dt),cnm(Cnm)], [abc(x),cnm(symbols)] ).
 Cnm = symbols
 options_call(+Opt, +Goal, +Opts)
Call Goal iff =options(Opt,Opts)= succeeds.
Opts can in addition to Opt include call_module(Mod=user) which defines the calling module if one is not in Goal
?- options_call( write(true), (write(true),nl), write(true) ).
?- options_call( write(flase), (write(true),nl), write(false) ).
?- options_call( write(true), user:(write(true),nl), write(true) ).
- nicos angelopoulos
- 0.1 2017/2/15
 options_call(+Goal, +Opts)
Call Goal by extending it with a first argument that comes from selecting a homonymous option from Opts.
Opts call_module(Mod=user) the module in which to call extended Goal
?- options_call( plus(2,X), plus(1) ).
X = 3
- nicos angelopoulos
- 0.1 2015/12/15 @ allow for , separate goals ?
 options_debug_topic(+Topic, +Opts, -Restore)
Start debugging Topic iff options(debug(true),Opts), with Restore being instantiated to a term that can be used to restore the original debug state of Topic (see options_restore/2).
?- options_debug_topic( ex1, [debug(false)], Restore ).
Restore = [].

?- options_debug_topic( ex1, [debug(true)], Restore ).
Restore = ['$restore'(ex1, debug, false)].
- nicos angelopoulos
- 0.1 2016/8/22
 options_version(-Version, -Date)
Current version and release date for the library.


?- options_version( Vers, Date ).
Date = date(2018,4,8),
Vers = 1:1:0.
 options(+Required, +Opts)
 options(+Required, +Opts, +OptionsOpts)
This should more naturally be option/2 but as this might cause confusion with Swi's own option library. Required can be a single or list of terms.

Opts can also be non list as it is passed through en_list/2.


when true it enlists the returning argument
should the selected option required to be ground, and what to do if not
dont do anything
throw error
only variable is allowed, if present the call always succeeds and TruthValue is bound to either true or false depending on underlying success of options/2 call
RemOpts is Opts after all functor/shape matching mentions of Required have been removed.

The predicate fails silently if the first Required option with equivalent "shape" in Opts fails to pattern match (unlike classic memberchk/2).

 ?- options( x(y), [x(x)] ).
 ?- options( x(y), [x(x),x(y)] ).

 ?- options( x(X), [a(b),c(d),x(y),x(x)] ).

 ?- options( [a(X),c(b)], [a(b),x(x),b(c)] ).
 ERROR: Required option: c(b), not present in options: [a(b),x(x)]
 % Execution Aborted
 ?- options( x(X), [a(b),c(d),x(y),x(x)], rem_opts(Rem) ).
 X = y,
 Rem = [a(b), c(d)].

 ?- options( x(X), [a(b),c(d),x(y),x(x)], en_list(true) ).
 X= [y].

 ?- options( a(A), [a(X),b(c)], ground(error) ).
 ERROR: pack(options): Option should be ground, but found: a(_G1470), in options: [a(_G1470),b(c)]
 ?- options( a(A), [a(X),b(c)], ground(true) ).
 ?- options( a(A), [a(X),b(c)] ).
 A = X.
 ?- options( a(A), [a(X),b(c)], ground(false) ).
 A = X.
 ?- options( a(b), [a(a),a(b),b(c)], true(T) ).
 T = fail.
 ?- options( a(A), [a(a),a(b),b(c)], true(T) ).
 A = a,
 T = true.
 ?- options( a(a), [a(a),a(b),b(c)], true(T) ).
 T = true.
- nicos angelopoulos
- 0.2 2015/01/16
- 0.3 2015/12/06 changed 3rd argument to Options of its own invocation