haskCoq :: [a] -> List a
haskCoq [] = Nil
haskCoq (h : hs) = Cons h (haskCoq hs)

coqNat :: P.Int -> Nat
coqNat n
  | n P.== 0 = O
  | P.otherwise = S (coqNat (n P.- 1))


wordsWhen :: (P.Char -> P.Bool) -> P.String -> [P.String]
wordsWhen p s =  case L.dropWhile p s of
                      "" -> []
                      s' -> w : wordsWhen p s''
                            where (w, s'') = L.break p s'


balfun :: [(Cand, Nat)] -> (Ballot Cand)
balfun [(A, b1), (B, b2), (C, b3), (D, b4)] = f where
  f :: Cand -> Nat
  f A = b1
  f B = b2
  f C = b3
  f D = b4


main :: IO ()
main = do
   r <- getContents
   let votes = P.map (balfun P..
               L.sort P.. P.map (\(y, z) -> (y, coqNat z)) P..
               P.map (\x -> P.read x :: (Cand, P.Int)) P..
               wordsWhen (P.== ';')) P.. P.lines P.$ r
   P.print P.$ schulze_winners_pf (haskCoq votes)

I am trying to convert the Haskell code into Ocaml and below is my implementation.


let rec ocamlcoq l =
  match l with
  | [] -> Nil
  | h :: t -> Cons (h, (ocamlcoq t))

let rec ocamlnat n =
  match n with
  | 0 -> O
  | _ -> S (ocamlnat (n -1))

let balfun l =
   match l with
   | [(A, b1); (B, b2); (C, b3); (D, b4)] ->
        let f A = b1 in
        let f B = b2 in
        let f C = b3 in
        let f D = b4 in  f
   | _ -> failwith "failed to match pattern"


let input_line_opt ic =
  try Some (input_line ic)
  with End_of_file -> None

let read_lines ic =
  let rec aux acc =
    match input_line_opt ic with
    | Some line -> aux (line::acc)
    | None -> (List.rev acc)
  in
  aux []

let lines_of_file filename =
  let ic = open_in filename in
  let lines = read_lines ic in
  close_in ic;
  lines


let process_input filename =
  let lines = lines_of_file filename in
  List.map (fun x -> Str.split (Str.regexp ";") x) lines

 Input file is

(A,3);(B,1);(C,2);(D,4)
(A,1);(B,0);(C,4);(D,3)
(A,3);(B,1);(C,2);(D,4)
(A,2);(B,3);(C,3);(D,4)
(A,3);(B,1);(C,2);(D,4)
(A,1);(B,2);(C,3);(D,4)
(A,1);(B,2);(C,3);(D,4)
(A,1);(B,2);(C,2);(D,4)
(A,1);(B,2);(C,2);(D,4)
(A,1);(B,3);(C,2);(D,4)

utop[34]> process_input "example-votes.txt";;
- : string BatList.t BatList.t =
[["(A,3)"; "(B,1)"; "(C,2)"; "(D,4)"]; ["(A,1)"; "(B,0)"; "(C,4)"; "(D,3)"];
 ["(A,3)"; "(B,1)"; "(C,2)"; "(D,4)"]; ["(A,2)"; "(B,3)"; "(C,3)"; "(D,4)"];
 ["(A,3)"; "(B,1)"; "(C,2)"; "(D,4)"]; ["(A,1)"; "(B,2)"; "(C,3)"; "(D,4)"];
 ["(A,1)"; "(B,2)"; "(C,3)"; "(D,4)"]; ["(A,1)"; "(B,2)"; "(C,2)"; "(D,4)"];
 ["(A,1)"; "(B,2)"; "(C,2)"; "(D,4)"]; ["(A,1)"; "(B,3)"; "(C,2)"; "(D,4)"]]

 I am looking for function to convert "(A,3)" : string to (A, 3) : cand * int