[erlang-questions] builtin regexp functions in Erlang/OTP R12B-3

Mats Cronqvist <>
Mon Jun 16 17:53:06 CEST 2008

Kenneth Lundin wrote:
> Hi,
> Regarding the new "experimental" builtin regexp functions in the re
> module our intention is
> to provide a fully working implementation where we want feedback on
> the API functions and also other feedback.
> With "experimental" we don't mean very buggy or low quality but rather
> that the API's are not stabilized yet and that there
> are a few optimizations more to do.
> Our intention with releasing this regexp implementation before the
> API's are 100% settled is that we believe
> we can get more and better comments if people actuall can try
> themselves to use the functions.
> We would appreciate if we get the comments in relation to the
> EEP 11 Built in regular expressions in Erlang
> http://www.erlang.org/eeps/eep-0011.html which is especially written
> for this purpose.

  i'd like to add this the EEP11;

  since implementing regular expressions with backreferences is an 
NP-complete problem, "re" disallows backreferences. this is achieved by 
calling pcre_fullinfo() and requiring that PCRE_INFO_BACKREFMAX == 0.

 from http://www.pcre.org/pcre.txt:

 int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
            int what, void *where);


       The  possible  values for the third argument are defined in pcre.h, and
       are as follows:


       Return the number of the highest back reference  in  the  pattern.  The
       fourth  argument  should  point to an int variable. Zero is returned if
       there are no back references.

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