On Sunday 12 April 2009 3:42:35 pm Anatoly Yakovenko wrote:
i am trying to figure out how typeable works, so i have this data type
data Foo = FooC Int deriving (Data, Typeable, Show)
So how come this works:
funResultTy (typeOf ((+) 1)) (typeOf 1)
Just Integer
but this doesnt:
funResultTy (typeOf FooC) (typeOf 1)
Nothing
FooC is of type t -> u and 1 is of type t so the result should be u? I don't think t and u need to be the same since
funResultTy (typeOf (\a -> a:[1])) (typeOf 1)
Just [Integer]
works fine. So given a constructor, how come i cant seem to construct a type out of it?
Judging from the other types, 'typeOf 1' is defaulting to Integer. FooC, per your declaration, has type 'Int -> Foo'. So, you're probably asking it what happens when you apply an Int -> Foo to an Integer, which would be a type error, and explains the Nothing, I think. -- Dan