    1:- module(
    2  type_ext,
    3  [
    4    boolean/1,         % @Term
    5    positive_integer/1 % @Term
    6  ]
    7).

Extended support for types

Extends support for types in the SWI-Prolog standard library.

This module introduces the following types:

options: A dictionary with tag options that is used to represent options passed to predicates.

   20:- use_module(library(error)).   21:- use_module(library(lists)).   22
   23:- use_module(library(dict)).   24
   25:- multifile
   26    error:has_type/2.   27
   28error:has_type(maybe(Type), Term) :-
   29  ( error:has_type(Type, Term)
   30  ; error:has_type(var, Term)
   31  ).
   32error:has_type(options, Term) :-
   33  error:has_type(dict, Term),
   34  dict_key(Term, options).
   35error:has_type(or(Types), Term) :-
   36  member(Type, Types),
   37  error:has_type(Type, Term), !.

boolean(@Term) is semidet

   43boolean(false).
   44boolean(true).

positive_integer(@Term) is semidet

   50positive_integer(Term) :-
   51  error:has_type(positive_integer, Term)