On Dec 3, 2007 7:43 AM, Peter Padawitz
What is wrong here? ghci tries (and fails) to deduce certain types for the comp functions that I did not expect.
type Block = [Command] data Command = Skip | Assign String IntE | Cond BoolE Block Block | Loop BoolE Block data IntE = IntE Int | Var String | Sub IntE IntE | Sum [IntE] | Prod [IntE] data BoolE = BoolE Bool | Greater IntE IntE | Not BoolE
class Java block command intE boolE where block_ :: [command] -> block skip :: command assign :: String -> intE -> command cond :: boolE -> block -> block -> command loop :: boolE -> block -> command intE_ :: Int -> intE var :: String -> intE sub :: intE -> intE -> intE sum_ :: [intE] -> intE prod :: [intE] -> intE boolE_ :: Bool -> boolE greater :: intE -> intE -> boolE not_ :: boolE -> boolE
compBlock :: Block -> block compBlock = block_ . map compCommand
compCommand :: Command -> command compCommand Skip = skip compCommand (Assign x e) = assign x (compIntE e) compCommand (Cond be c c') = cond (compBoolE be) (compCommand c) (compCommand c') compCommand (Loop be c) = loop (compBoolE be) (compCommand c)-}
compIntE :: IntE -> intE compIntE (IntE i) = intE_ i compIntE (Var x) = var x compIntE (Sub e e') = sub (compIntE e) (compIntE e') compIntE (Sum es) = sum_ (map compIntE es) compIntE (Prod es) = prod (map compIntE es)
compBoolE :: BoolE -> boolE compBoolE (BoolE b) = boolE_ b compBoolE (Greater e e') = greater (compIntE e) (compIntE e') compBoolE (Not be) = not_ (compBoolE be)
Well, first of all, the definition of compCommand should use calls to compBlock, not recursive calls to compCommand. But that's not the main source of your problems. What exactly are you trying to accomplish? And why do you need a type class? -Brent