PublicShow sourceoption.pl -- 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 of 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),
        ...

Options typically have exactly one argument. The library does support options with 0 or more than one argument with the following restrictions:

See also
- library(record)
- Option processing capabilities may be declared using the directive predicate_options/3.
To be done
- We should consider putting many options in an assoc or record with appropriate preprocessing to achieve better performance.
Source option(?Option, +OptionList, +Default) is semidet
Get an Option from OptionList. OptionList can use the Name=Value as well as the Name(Value) convention.
Arguments:
Option- Term of the form Name(?Value).

Undocumented predicates

The following predicates are exported, but not or incorrectly documented.

Source select_option(Arg1, Arg2, Arg3)
Source option(Arg1, Arg2)
Source select_option(Arg1, Arg2, Arg3, Arg4)
Source meta_options(Arg1, Arg2, Arg3)
Source dict_options(Arg1, Arg2)
Source merge_options(Arg1, Arg2, Arg3)