Hello all, Is is possible to apply numeric defaulting while looking for matching instance declarations? For example, I'd like the following code to work without having to explicitly specify the type of "7":
module Main where class Stuff a b c | a b -> c where hi :: a -> b -> c instance Stuff Integer Bool Bool where hi a b = if b then True else a == 0 instance Stuff Float Bool Bool where hi a b = if b then False else a < 12.0 main = do --putStrLn $ show $ hi 7 True -- doesn't work putStrLn $ show $ hi (7::Integer) True -- works Under normal circumstances, the value of 7 would default to 7::Integer, but this doesn't occur when type classes are involved this way. Instead GHC complains of 'No instance for (Stuff a Bool c)' Obviously, I can just insert '::Integer' everywhere, but that is the problem defaulting was designed to solve, and besides, its really irritating and ugly. BTW I already tried using Data.Typeable to determine the correct types and cast at runtime, but GHC won't default over the constraint: (Typeable a, Num a) because, I suppose, Typeable is not a standard type class (Haskell Report section 4.3.4) Any ideas? Thanks, Robert
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