Question

I have this function which removes occurrences of a given element within the list of lists.

remove          :: Eq a => a -> [[a]] -> [[a]]
remove    y []  = error "Can't remove an element from an empty list"
remove    y xs  = map (filter(/=y)) xs

How would I be able to do the same using List comprehension

Thank you

Answer 1

For each l in xs, add filter (/= xs) l to the resulting list:

remove y xs = [filter (/= y) l | l <- xs]

or, removing filter by nesting comprehensions.
For each xs in xss and for each x in xs, keep x only if it’s different from y:

remove y xss = [ [x| x <- xs, x /= y] | xs <- xss]

It’s OK if you’re just practicing , but your version with map is way better 🙂