On Fri, Jul 19, 2013 at 5:19 AM, Jose A. Lopes
Hello,
How to define equality for Data.Dynamic ?
Hi Jose, You could try casting the values to different types that do have an (==). You can treat the case where you have the types matching, but didn't list that type beforehand differently. eqTys a b | Just a' <- fromDynamic a, Just b' <- fromDynamic b = a' == (b' :: Int) | Just a' <- fromDynamic a, Just b' <- fromDynamic b = a' == (b' :: Integer) | show a == show b = error "equal types, but don't know if there's an (==)!" | otherwise = False {-
eqTys (toDyn 4) (toDyn 5) False
eqTys (toDyn 4) (toDyn 4) True
eqTys (toDyn 4) (toDyn 4.5) False
eqTys (toDyn 4.5) (toDyn 4.5) *** Exception: equal types, but don't know if there's an (==)!
-} -- Adam