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.

<lang ocaml>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"</lang>

We provide an additional function to create new lang parameters from simple data set:

<lang ocaml>type lang_set = (int * char list) list

let make_lang ss =

 let ss = List.map (fun (d, li) -> string_of_int d, li) ss in
 let ss = List.map (fun (d, li) -> List.map (fun c -> c, d) li) ss in
 let ss = List.flatten ss in
 (fun c -> try List.assoc c ss with Not_found -> "")</lang>

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

<lang ocaml>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</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:

<lang ocaml>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</lang>

We can run this test file with:

ocaml soundex.cmo test.ml