deep.icl

   1 module deep
   2
   3 import StdEnv
   4
   5 :: DSL
   6         = Lit Int
   7         | Plus DSL DSL
   8         | Div DSL DSL
   9
  10 eval :: DSL -> Int
  11 eval (Lit i) = i
  12 eval (Plus x y) = eval x + eval y
  13 eval (Div x y) = eval x / eval y
  14
  15 //Start = eval (Plus (Lit 41) (Lit 1))
  16
  17 import Control.Applicative
  18 import Control.Monad
  19 import Data.Functor
  20 import Data.Maybe
  21
  22 evalM :: DSL -> Maybe Int
  23 evalM (Lit i) = pure i
  24 evalM (Plus x y) = (+) <$> evalM x <*> evalM y
  25 evalM (Div x y) = evalM x >>= \x->evalM y >>= \y->case y of
  26         0 = Nothing
  27         x = Just (x / y)
  28
  29 Start = evalM (Plus (Lit 41) (Lit 1))