prolog_format.pl -- Analyse format specifications

This library parses the format specification used by format/1, format/2 and format/3. The parsed specification can be used to validate the consistency of the format string and the provided arguments. For example:

?- format_types('~d bottles of beer', Types).
Types = [integer].

author

- Michael Hendricks

See also

- http://www.swi-prolog.org/pack/list?p=format_spec

To be done

- The current implementation does not support format_predicate/2.

 format_spec(+Format, -Spec:list) is det

Parse a format string. Each element of Spec is one of the following:

text(Text)

Text sent to the output as is

escape(Num, Colon, Action)

A format escape. Num represents the optional numeric portion of an esape. Colon represents the optional colon in an escape. Action is an atom representing the action to be take by this escape.

 format_spec(-Spec)// is det

DCG for parsing format strings. It doesn't yet generate format strings from a spec. See format_spec/2 for details.

 format_types(+Format:text, -Types:list) is det

True when Format requires an argument list with terms of the type specified by Types. The length of this list is the number of arguments required. Each value of Types is a type as described by error:has_type/2.

 spec_types(+FormatSpec, -Types:list(type)) is det[private]

True if FormatSpec requires format/2 to have arguments of Types. Each value of Types is a type as described by error:has_type/2. This notion of types is compatible with library(mavis).

 is_action(+Action:integer) is semidet[private]

is_action(-Action:integer) is multi[private]

True if Action is a valid format/2 action character. Iterates all acceptable action characters, if Action is unbound.

 action_types(?Action:integer, ?Types:list(type))[private]

True if Action consumes arguments matching Types. An action (like ~), which consumes no arguments, has Types=[]. For example,

?- action_types(0'~, Types).
Types = [].
?- action_types(0'a, Types).
Types = [atom].