Question

I’m trying to get this piece of haskell code to work, however I keep getting this error message:

> ERROR file:.\4.hs:9 - Type error in application
> Expression     : fact n div (fact m * fact (n - m))
> Term           : fact
> Type           : Int -> Int
> Does not match : a -> b -> c -> d

Here’s the code:

fact :: Int -> Int
fact q 
 | q == 1 = 1
 | otherwise = q * fact(q-1)

comb :: Int -> Int -> Int
comb n m
 | n < m = error "undefined as n < m"
 | otherwise = ((fact n) div ((fact m) * (fact (n - m))))

Any idea how to fix it?

Answer 1

The problem is div in the last line.

When you want to make a function infix, you have to write it between `. So, simply change the last line to:

| otherwise = ((fact n) `div` ((fact m) * (fact (n - m))))