ocaml_result.ml

module Result = struct
  type ('a, 'b) t = Ok of 'a | Error of 'b

  let return a = Ok a

  let map f m = 
    match m with 
    | Ok a -> Ok (f a) 
    | Error b -> Error b

  let map_error f m = 
    match m with 
    | Ok a -> Ok a
    | Error b -> Error (f b)

  let bind f m = 
    match m with 
    | Ok a -> f a 
    | Error b -> Error b

  let ( >>= ) m f = bind f m
end

let info d = Printf.printf "%d\n" d

let plus a b = a + b

let add a b log = log a ; log b ; a + b

open Result


let _ =
  let four = Ok 4 in
  let three = Ok 3 in
  let res = four 
    >>= (fun a -> three |> map (plus a))
  in
  res 
    |> map print_int 
    |> map_error print_string