[Haskell-beginners] Type signature question

[Matthew Lefavor]

On Tue, Jul 23, 2013 at 10:33 AM, Louis-Guillaume Gagnon <
louis.guillaume.gagnon at gmail.com> wrote:

> 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
>

"Eq a" is the "Type class" of "a". It means that "a" is a type that
supports the checking of equality.

Other type classes include: "Show" (types that are printable), and "Ord"
(types that are orderable).

Cheers,

MCL
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