test.icl

   1 module test
   2
   3 import StdEnv
   4 import Data.Maybe
   5 import Data.Functor
   6 import Control.Monad
   7 import Control.Applicative
   8
   9 class expr v where
  10         lit :: i -> v i | toString i
  11         (+.) infixl 6 :: (v i) (v i) -> v i | + i
  12
  13 instance + (v a) | expr v & + a where
  14         + l r = l +. r
  15
  16 eval :: (Maybe a) -> Maybe a
  17 eval x = x
  18 instance expr Maybe where
  19         lit i = Just i
  20         +. x y = (+) <$> x <*> y
  21
  22 :: Print a =: Print String
  23 print :: (Print a) -> String
  24 print (Print a) = a
  25 instance expr Print where
  26         lit i = Print (toString i)
  27         +. (Print l) (Print r) = Print (l +++ "+" +++ r)
  28
  29 printEval :: (A.v: v a | expr v) -> (Maybe a, String)
  30 //printEval f = (f, let (Print p) = f in p)
  31 printEval f = (eval f, print f)
  32
  33 //Mag niet
  34 //Start :: (Maybe Int, String)
  35 //Start = printEval (lit 4 + lit 38)
  36
  37 //Mag wel
  38 Start = let (Print f) = lit 4 + lit 38 in f