constraint/test.icl

   1 module test
   2
   3 import StdEnv
   4
   5 class expr v c
   6 where
   7         lit :: a -> v (c a)
   8
   9 //class plus v c
  10 //where
  11 //      (+.) infixl 6 :: (v c a) (v c a) -> v c a | + a
  12
  13 :: BM x y = { to :: x -> y, fro :: y -> x }
  14 bm :: BM a a
  15 bm = {to=id, fro=id}
  16
  17 :: ToString a = E.e: ToString (BM a e) & toString e
  18
  19 :: Printer a = P a ([String] -> [String])
  20 :: PrintConstraints a = E.e: PC (BM a e) & toString e
  21
  22 print :: (Printer (PrintConstraints a)) -> [String]
  23 print (P _ a) = a []
  24
  25 instance expr Printer PrintConstraints
  26 where
  27         lit a = P (PC bm) \c->[toString (bm.to a):c]
  28 //instance plus Printer PrintConstraints
  29 //where
  30 //      (+.) (P l) (P r) = P \c->["(":l ["+":r [")":c]]]
  31
  32 //:: Eval c a = E a | EBlurp (c a)
  33 //:: EvalConstraints a = EC a
  34 //eval :: (Eval EvalConstraints a) -> a
  35 //eval (E a) = a
  36 //
  37 //instance expr Eval EvalConstraints
  38 //where
  39 //      lit a = E a
  40 //instance plus Eval PrintConstraints
  41 //where
  42 //      (+.) (E l) (E r) = E (l + r)
  43
  44 Start = print t
  45 where
  46         t = lit 42