gistfile1.txt

:- module(clpstr, [
              cl_len/2,
              cl_regex/2,
              cl_insensitive/2,
              cl_str/1
          ]).
/** <module> Constraint Logic Programming over strings
 *
 * constraints over 'real' strings
 */

:- use_module(library(chr)).
:- use_module(library(clpfd)).

:- chr_constraint cl_len/2, cl_regex/2, cl_insensitive/2, cl_str/1.

%!   cl_len(+Str:text, +Len:integer) is semidet
%
%    adds a constraint on Str to be Len
%

% only one length constraint
cl_len(Str, Len1) \ cl_len(Str, Len2) <=>  Len1 #= Len2.
% we only test length once
cl_len(Str, Len) <=> ground(Str) |
    (string(Str) ; is_list(Str) ; atom(Str)),
    string_length(Str, X),
    X #= Len.

% in a real library we'd try to figure out if there were
% length constraints inconsistent with shortest possible match, or
% impossible to satisfy between two regexs.
% we also might want to have a wrapper prolog that compiles the regex
% and have some extended copy_term that copies the constraints
cl_regex(Regex, Str) <=> ground(Str), ground(Regex) | re_match(Regex, Str).

cl_insensitive(A,B) <=> ground(A), ground(B) |
                        string_lower(A, L),
                        string_lower(B, L).

cl_str(A) <=> \+ var(A) | string(A).