[Haskell-beginners] A simple function V2

[Brent Yorgey]

On Fri, Aug 31, 2012 at 09:01:30AM -0300, Ezequiel Hernan Di Giorgi wrote:
> 
> *intercalate :: (Eq t) => [t] -> [t] -> [t]*
> *intercalate (x:xs) (y:ys)*
> * | xt == [] = []*
> * | yt == [] = []*
> * | otherwise = x : y : intercalate xs ys*
> * where xt=(x:xs)*
> *            yt=(y:ys)*

I should also point out that the tests xt == [] and yt == [] will
never be true!  That is because xt is defined to be (x:xs) and yt is
(y:ys).  A list can be *either* the empty list [], or a cons like
(x:xs), but not both.

-Brent