Question

I would like to have a function that checks if a list contains only even numbers; if so, it should return True, otherwise – False.

Functions I would like to use are map / filter / foldr, possibly without length.

Here is my attempt:

ListOfeven :: [Integral] -> Bool
ListOfeven xs = 
  | foldr (+) True filter odd xs < 0 = True
  | otherwise = False

I am pretty sure that there is a cleaner way.. isn’t there any? 🙂

Answer 1

The easiest would be to just use the all function from the Prelude:

evenList = all even

If you insist on just using map, filter and foldr:

evenList = foldr (&&) True . map even