open import "prelude.ml"

class pretty 'a begin
  val pretty : 'a -> int -> string
end

type prettyable =
  | S : show 'a => 'a -> prettyable
  | P : pretty 'a => 'a -> prettyable

let dummy_pretty = pretty

instance pretty prettyable begin
  let pretty x w =
    match x with
    | S a -> show a
    | P a -> dummy_pretty a w
end

class prettyrecord 'r begin
  val name : 'r -> string
  val fields : 'r -> list (string * prettyable)
end

instance prettyrecord 'a => pretty 'a begin
  let pretty a w =
    let rec smul s n =
      if n <= 0 then
        ""
      else
        s ^ (smul s (n - 1))
    let x = w + 2
    let prep = smul " " w
    let rf = fields a
    let rec field_str acc l =
      match l with
      | [] -> acc
      | Cons ((name, field), xs) -> field_str (acc ^ prep ^ "  " ^ name ^ " = " ^ (pretty field x) ^ ",\n") xs
    let body = field_str "" rf
    (name a) ^ " {\n" ^ body ^ prep ^ "}"
end