import Html exposing (text)
import Text
type Term = Con Int
          | Div Term Term

type alias M a = (Output, a)
type alias Output = String

unit : a -> M a
unit a = ("", a)

flatMap : M a -> (a -> M b) -> M b
flatMap m k = 
    let (x,a) = m   in
    let (y,b) = k a in
    (x++y, b)

eval : Term -> M Int
eval term = 
  case term of
    Con a -> flatMap (out(line(Con a) a)) (\() -> unit(a))
    Div t u ->
      flatMap (eval t)(\a ->
        flatMap (eval u)(\b -> 
          flatMap(out(line(Div t u)(a//b))) (\() -> unit(a//b))
        )
      )

out : Output -> M ()
out x = (x, ())

line : Term -> Int -> Output
line t a = "eval(" ++ (toString t) ++ ") <= " ++ (toString a)

main = text (toString (eval (Div(Div(Con 1972)(Con 2))(Con 23))))