Count the number of values in a nested list that are greater and less than certain values

I'm working on a function for a homework problem that counts the number of values in a list for which the values are greater than v1 and less than v2. I've put something together that works but only in a specific case. When I try something else I get the error of

*** Exception: Non-exhaustive patterns in function countInRange

This function is supposed to call on getInRange. getInRange just returns values from a list that are greater than v1 and less than v2. Here is what it looks like.

rangeHelper v1 v2 x | x > v1 && x < v2 = True
                    | otherwise = False

getInRange :: Ord a => a -> a -> [a] -> [a]
getInRange v1 v2 iL = filter(rangeHelper v1 v2) iL

count iL = sum (map (const 1) iL)

countInRange :: Ord a => a -> a -> [[a]] -> Int
countInRange v1 v2 [iL] = count ((getInRange v1 v2) iL)

If I were to call

countInRange 3 10 [[4,5,6]]         -- works, prints 3
countInRange 3 10 [[1,2], [4,5,6]]  -- error: non exhaustive patterns

Your countInRange function only expects a list that contains one list. When you write countInRange v1 v2 [iL] you only define it to match pattern when your list contains single element called iL. You can also use count = length

You can fix this issue by defining it like this:

countInRange v1 v2 xs  = sum (map (length.filter (rangeHelper v1 v2)) xs)
-- or
countInRange v1 v2     = sum.map (length.filter (rangeHelper v1 v2))