Show the type of something if no Show instance is available

@hvr You might like this!

λ> 1
1
λ> id
it :: a -> a
λ> map
it :: (a -> b) -> [a] -> [b]
λ> map (*2)
it :: [Integer] -> [Integer]
λ> map (*2) [1..5]
[2,4,6,8,10]