isPalindrome xs
     | odd (length xs)              = False
     | firstHalf == secondHalf =True
     | otherwise                       = False
     where half              = div (length xs) 2
                firstHalf       = take half xs
                secondHalf = reverse (drop half xs)

I would expect the type signature to be:
isPalindrome :: [a] -> Bool

but ghci gives me
is Eq a => [a] -> Bool

and I don't undestand why the "Eq a =>" shows up