Soundex/OCaml

From Rosetta Code

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"

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

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 -> "")

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