Question

I want to list all integers that divide n. This is a homework question. So far I have done this.

divisors :: Int -> [Int]
divisors n | n < 1 = []
           | otherwise = filter (\n -> n `mod` x == 0) [1..n]
             where x = [1..n]

I know this is wrong, but I am not getting the right filter predicate. I don’t know how the syntax is for doing this. and ofcourse I cannot use n mod n since that is just lists all elements 1 to n.

Answer 1

You want to check if mod n k == 0 for each k from 1 to n. The n is fixed (the argument of divisors) and the k varies, i.e. that is what should be the argument of the lambda expression

| otherwise = filter (\k -> n `mod` k == 0) [1 .. n]