options
This library provides useful predicates for managing developer tool and application options.
API documentation
Open the ../../docs/library_index.html#options file in a web browser.
Loading
To load all entities in this library, load the loader.lgt utility
file:
| ?- logtalk_load(options(loader)).
Testing
To test this library predicates, load the tester.lgt file:
| ?- logtalk_load(options(tester)).
Usage
The options category is usually imported by the root object of the
developer tool or application. The importing object should define the
default_option/1 predicate and, if option type-checking is required,
the valid_option/1 predicate must be defined for each option. This
library requires options to be represented by compound terms where the
functor is the option name (e.g. trim(true) or (box(0,2))). The
option/2-3 can be used to get or test an option given a list of
options. When an option appears multiple times in a list, the
option/2-3 predicates get or test the first (leftmost) occurrence.
The library also supports a user-defined fix_option/2 predicate. An
usage example is when an option value can be a relative file path that
should be expanded before used. Another usage example would be
converting from a user-friendly option to a form more suitable for
internal processing. When a call to the fix_option/2 predicate
fails, the option is used as-is.
A simple example:
:- object(foo,
imports(options)).
:- uses(type, [
valid/2
]).
:- public(p/0).
p :-
% use default options
p([]).
:- public(p/1).
p(UserOptions) :-
^^check_options(UserOptions),
% construct the full set of options from
% the user options and the default options
^^merge_options(UserOptions, Options),
...
% query an option
^^option(baz(Boolean), Options),
q(Boolean),
...
default_option(baz(true)).
...
valid_option(baz(Boolean)) :-
valid(boolean, Boolean).
...
:- end_object.
Note that you can use protected or private import of the options
category if you don’t want to add its public predicates to the object
protocol.