Transpose in ocaml

transpose.ml

let matrix_hd = fun matrix -> List.fold_left (fun acc x -> (List.hd x) :: acc) [] matrix |> List.rev

let matrix_tl = fun matrix -> List.fold_left (fun acc x -> (List.tl x) :: acc) [] matrix |> List.rev

let transpose = fun matrix ->
  let rec loop = fun acc matrix ->
  match matrix with
  | hd :: tl when (List.length hd) = 0 -> acc
  | x -> loop ((matrix_hd x) :: acc) (matrix_tl x) in
  loop [] matrix |> List.rev