re_foldl/6

Documentation
- Reference manual
- Packages
  - SWI-Prolog Regular Expression library
    - library(pcre): Perl compatible regular expression matching for SWI-Prolog

Availability::- use_module(library(pcre)).(can be autoloaded)

[semidet]re_foldl(:Goal, +Regex, +String, ?V0, ?V, +Options)

Fold all matches of Regex on String. Each match is represented by a dict as specified for re_matchsub/4. V0 and V are related using a sequence of invocations of Goal as illustrated below.

call(Goal, Dict1, V0, V1),
call(Goal, Dict2, V1, V2),
...
call(Goal, Dictn, Vn, V).

This predicate is used to implement re_split/4 and re_replace/4. For example, we can count all matches of a Regex on String using this code:

re_match_count(Regex, String, Count) :-
    re_foldl(increment, Regex, String, 0, Count, []).

increment(_Match, V0, V1) :-
    V1 is V0+1.

After which we can query

?- re_match_count("a", "aap", X).
X = 2.