Regular Expressions in OCaml

23
votes

I want to use regexps in OCaml and it seems that Str module provides these functionalities.

So I tried with a simple program:

open Str
let regx = regexp "."

but it gives me the following error

File "lol.ml", line 1, characters 0-1: Error: Error while linking lol.cmo: Reference to undefined global `Str'

As if module is not present but if I remove open Str it says that regexp is an unbound value.

I don't get what kind of issue it is, Str should be a standard module (according to http://caml.inria.fr/pub/docs/old-311/libref/Str.html) so I'm clueless.. the only think I thought is that signature (mli) is present but implementation (ml) is not.

I'm running Objective Caml version 3.11.0 according to ocaml tool.

Can anyone help me figuring this out? Thanks in advance

3
regexmodulelinkerocaml
If you can avoid it, you really don't want to use the Str module. Its API is non-reentrant, leading to all manner of problems. Fortunately, PCRE has good OCaml bindings at: ocaml.info/home/ocaml_sources.html You might also want to check out Mikmatch for syntax support on top of the PCRE engine. – Michael Ekstrand

3 Answers

30
votes

From the manual:

Programs that use the str library must be linked as follows:

ocamlc other options str.cma other files
ocamlopt other options str.cmxa other files
22
votes

Or you can put

#load "str.cma";;

if you are doing it in the interpreter

3
votes

As an alternative to the Str module there's also Re2.

  1. Install it using opam install re2

  2. Use the module in your_file.ml like this:

    open Re2.Std
open Re2.Infix
let change input_text = Re2.rewrite_exn ~/"change this" "to that" input_text
let () = printf "%s" (change "change this")

  3. Compile with ocamlbuild -use-ocamlfind -package re2 -package core -tag thread your_file.byte