It sounds like you want to include x only if it is not already at the head
of the list. Try this:
extractIfBegins x (y:ys)
| x == y = ys
| otherwise = x:ys
On Sat, Dec 26, 2015 at 9:19 AM, Fabien R
As a newbie, I'm studying the pdf 'the Haskell road to logic, math and programming' and I'm stuck with one exercise. I want to extract x if x is at the beginning of a list. I thought to use something like this: extractIfBegins x [xs] | [xs] == (x:ys) = [ys] | otherwise = [xs]
But ghci complains that ys is not defined. Without giving the answer, can someone give a hint about the approach to follow ?
-- Fabien _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners