On Mon, 15 Sep 2008, Tom Hawkins wrote:
OK. But let's modify Expr so that Const carries values of different types:
data Expr :: * -> * where
Const :: a -> Term a
Equal :: Term a -> Term a -> Term Bool
How would you then define:
Const a === Const b = ...
Apart from the suggestions about Data.Typeable etc, one possibility is to
enumerate the different possible types that will be used as parameters to
Const in different constructors, either in Expr or in a new type.
So IntConst :: Int -> Expr Int, etc
Or Const :: Const a -> Expr a and IntConst :: Int -> Const Int etc
Not very pleasant though.
Ganesh
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