Why doesn't this definition cover all pattern cases?

Question

So I\'m trying to triplize an element, i.e. making 2 other copies of the element.

So I\'ve written this:

triplize :: [a] -> [a]
tripl         


        

Answer 1

[x] matches a list of exactly one element. If you want to match any list, just remove [ and ]:

triplize x = concatMap (replicate 3) x

This would turn ["a", "b", "c"] into ["a", "a", "a", "b", "b", "b", "c", "c", "c"].

On the other hand, if you want to take one element and return a list (containing 3 of that element), then your code should be

triplize :: a -> [a]
triplize x = replicate 3 x