Soundex/OCaml

Here is a version with very few changes, which allows choosing different languages (en for English, fr for French) of type lang, the definition of this type will be hidden in the interface.

type lang = char -> string

let en = function
  | 'B' | 'F' | 'P' | 'V' -> "1"
  | 'C' | 'G' | 'J' | 'K' | 'Q' | 'S' | 'X' | 'Z' -> "2"
  | 'D' | 'T' -> "3"
  | 'L' -> "4"
  | 'M' | 'N' -> "5"
  | 'R' -> "6"
  | _ -> ""

let fr = function
  | 'B' | 'P' -> "1"
  | 'C' | 'K' | 'Q' -> "2"
  | 'D' | 'T' -> "3"
  | 'L' -> "4"
  | 'M' | 'N' -> "5"
  | 'R' -> "6"
  | 'G' | 'J' -> "7"
  | 'X' | 'Z' | 'S' -> "8"
  | 'F' | 'V' -> "9"
  | _ -> ""

let rec dbl acc = function
  | [] -> (List.rev acc)
  | c::[] -> List.rev(c::acc)
  | c1::(c2::_ as tl) ->
      if c1 = c2
      then dbl acc tl
      else dbl (c1::acc) tl

let pad s =
  match String.length s with
  | 0 -> s ^ "000"
  | 1 -> s ^ "00"
  | 2 -> s ^ "0"
  | 3 -> s
  | _ -> String.sub s 0 3

let soundex_aux lang rem =
  pad(String.concat "" (dbl [] (List.map lang rem)))

let soundex ?(lang=en) s =
  let s = String.uppercase s in
  let cl = ref [] in
  String.iter (fun c -> cl := c :: !cl) s;
  match dbl [] (List.rev !cl) with
  | c::rem -> (String.make 1 c) ^ (soundex_aux lang rem)
  | [] -> invalid_arg "soundex"

in the interface as the definition of the type lang is hidden we can use it easily as a classic parameter:

type lang

val en : lang
val fr : lang

val soundex : ?lang:lang -> string -> string

type lang_set = (int * char list) list
val make_lang : lang_set -> lang

The lang parameter for the soundex function is optional, if omited the english set is used.

We put the implementation in the file soundex.ml and the interface in soundex.mli, then we compile with:

ocamlc -c soundex.mli
ocamlc -c soundex.ml

Test that the function make_lang provide the same results:

open Soundex

let tests = [
  "Soundex"; "Example"; "Sownteks"; "Ekzampul"; "Euler"; "Gauss"; "Hilbert";
  "Knuth"; "Lloyd"; "Lukasiewicz"; "Ellery"; "Ghosh"; "Heilbronn"; "Kant";
  "Ladd"; "Lissajous"; "Wheaton"; "Ashcraft"; "Burroughs"; "Burrows"; "O'Hara" ]

let fr_set = [
  1, ['B'; 'P'];
  2, ['C'; 'K'; 'Q'];
  3, ['D'; 'T'];
  4, ['L'];
  5, ['M'; 'N'];
  6, ['R'];
  7, ['G'; 'J'];
  8, ['X'; 'Z'; 'S'];
  9, ['F'; 'V'];
]

let my_fr = make_lang fr_set ;;

let () =
  print_endline " Word   \t Fr    Check Status";
  List.iter (fun word ->
    let code1 = soundex ~lang:Soundex.fr word in
    let code2 = soundex ~lang:my_fr word in
    let status = if code1 = code2 then "OK " else "Arg" in
    Printf.printf " \"%s\" \t %s  %s  %s\n" word code1 code2 status
  ) tests

We can run this test file with: ocaml soundex.cmo test.ml