RE: [Caml-list] help with regular expression

[David Allsopp <dra-news@metastack.com>]

zaid Khalid wrote:
> Hi Folks
>
> I want some help in writing regular expressions in Ocaml, as I know how to write it
> in informal way but in Ocaml syntax I can not. For example I want to write "a* | (aba)* ".

This question would better be posted on the beginners' list - http://caml.inria.fr/resources/forums.en.html#id2267683

Regular Expressions can be done using the Standard Library with the Str module (as you've found) - see http://caml.inria.fr/pub/docs/manual-ocaml/libref/Str.html so your expression above (assuming you have loaded/linked str.cm[x]a) is Str.regexp "a*\\|\\(aba\\)*". The language of regexps is given in the docs for Str.regexp function. Remember to escape backslash characters as the regular expression is given in an OCaml string (so to escape a backslash in your regexp you have to write "\\\\").

> Another question if I want the string to be matched against the regular expression
> to be matched as whole string not as substring what symbol I need to attach to the
> substring, i.e if I want only concrete strings accepted (like (" ", a , aa , aaa, 
> aba, abaaba), but not ab or not abaa).

Use ^ and $ at the beginning and end of your regexp to ensure that it matches the entire string only - "^\\(a*\\|\\(aba\\)*\\)$"

> Hint I am using (Str.regexp)

There are other libraries (e.g. pcre-ocaml) which provide different (I would say more powerful, rather than strictly better!) implementations.


David