yallop / ocaml-reex

Staged regular expression library for MetaOCaml

A staged regular expression library for MetaOCaml, based on "Regular-expression derivatives reexamined"

Installing reex

1. Install the BER MetaOCaml compiler using OPAM:

   opam switch 4.14.1+BER
   eval $(opam env)
   

2. Add the metaocaml-opam repository:

   opam remote add metaocaml git+https://github.com/metaocaml/metaocaml-opam.git
   

3. Install the reex and reex_match packages:

   opam pin add reex reex_match
   

Using reex

The functions in the Reex module construct regular expressions:

let letters = plus (range 'A' 'Z')   (* [A-Z]+ *)
let keyword = str "let" <|> str "and" <|> str "in"

Alternatively, the Reex.regex function builds a regular expression from a string:

let letters = regex "[A-Z]+"
let keyword = regex "let|and|in"

The Reex_match.match_ function generates OCaml code that matches one or more regular expressions. For example, the following call

.<fun i s ->
   .~(match_ ~options:{default_options with match_type=`ranges} .<i>. .<s>.
        [chr 'a'       , (fun _ _ -> .<"a">.);
         plus (chr 'b'), (fun _ _ -> .<"b">.)]) >.

generates the following OCaml code for matching "a" or "b+":

fun i s ->
  let rec f ~start ~index ~len s =
    match String.unsafe_get s index with
    | 'c'..'\255'|'\000'..'`' -> failwith "no match"
    | 'b' -> g ~start ~index:(index + 1) ~len s
    | 'a' -> h ~start ~index:(index + 1) ~len s
  and g ~start ~index ~len s =
    match String.unsafe_get s index with
    | 'c'..'\255'|'\000'..'a' -> "b"
    | 'b' -> g ~start ~index:(index + 1) ~len s
  and h ~start ~index ~len s = "a" in
  f ~start:i ~index:i ~len:(String.length s) s