Carlo Vivari wrote:
> data AlgExp a = AlgExp
> { litI :: Int -> a,
> litB :: Bool -> a,
> add :: a -> a -> a,
> and :: a -> a -> a,
> ifte :: a -> a -> a -> a}
You're confusing sum and product types. That is, you're using a product type,
but you probably need a sum type, like this:
data Exp1 = LitI Int
| LitB Bool
| Add Exp1 Exp1
| And Exp1 Exp1
| IfThenElse Exp1 Exp1 Exp1
But in this case, using GADTs (beware: not Haskell 98, but a very popular
extension) makes for a more elegant solution. Note the strong types, disallowing
e. g. the addition of a number to a boolean value:
data Exp2 a where
LitI :: Int -> Exp2 Int
LitB :: Bool -> Exp2 Bool
Add :: Exp2 Int -> Exp2 Int -> Exp2 Int
And :: Exp2 Bool -> Exp2 Bool -> Exp2 Bool
IfThenElse :: Exp2 Bool -> Exp2 a -> Exp2 a -> Exp2 a
Kalman
----------------------------------------------------------------------
Get a free email address with REAL anti-spam protection.
http://www.bluebottle.com/tag/1