rank2/test.icl

   1 module test
   2
   3 import StdEnv
   4
   5 class arith v
   6 where
   7         lit :: a -> v a | toString a
   8         plus :: (v a) (v a) -> v a | + a
   9
  10 class rtrn v :: (v a) -> v (TaskValue a)
  11
  12 :: Print a = P String
  13 unPrint :: (Print a) -> String
  14 unPrint (P a) = a
  15
  16 :: Eval a = E a
  17 unEval :: (Eval a) -> a
  18 unEval (E a) = a
  19
  20 :: TaskValue a = NoValue | Value a Bool
  21
  22 instance arith Print
  23 where
  24         lit a = P (toString a)
  25         plus (P a) (P b) = P (a +++ "+" +++ b)
  26
  27 instance arith Eval
  28 where
  29         lit a = E a
  30         plus (E a) (E b) = E (a + b)
  31
  32 instance rtrn Print where rtrn (P a) = P ("Task (" +++ a +++ ")")
  33 instance rtrn Eval where rtrn (E a) = E (Value a True)
  34
  35 class default a :: a
  36 instance default Int where default = 42
  37 instance default (TaskValue a) where default = NoValue
  38
  39 listItem ::
  40         (A.v: a -> v (TaskValue b) | rtrn, arith v)
  41         -> (String, b)
  42         | +, toString, default b & default a
  43 listItem mtask =
  44         ( unPrint (mtask default)
  45         , default //unEval (mtask default)
  46         )
  47
  48 Start :: (String, Int)
  49 Start = listItem \i->rtrn (lit i)