module deep

import StdEnv

:: DSL
	= Lit Int
	| Plus DSL DSL
	| Div DSL DSL

eval :: DSL -> Int
eval (Lit i) = i
eval (Plus x y) = eval x + eval y
eval (Div x y) = eval x / eval y

//Start = eval (Plus (Lit 41) (Lit 1))

import Control.Applicative
import Control.Monad
import Data.Functor
import Data.Maybe

evalM :: DSL -> Maybe Int
evalM (Lit i) = pure i
evalM (Plus x y) = (+) <$> evalM x <*> evalM y
evalM (Div x y) = evalM x >>= \x->evalM y >>= \y->case y of
	0 = Nothing
	x = Just (x / y)

Start = evalM (Plus (Lit 41) (Lit 1))