Type error in application

I'm 开发者_开发知识库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?

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))))

You are using div as infix, but it is not an operator so you have to write it like this:

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

or like this:

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

You have

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

but it should be

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

(at least)

Basically, you are using an infix operator, you'll have to mark it using back-quotes.

However, in this case, to reduce the number of parantheses, I'll rewrite it as

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

Edit: s/inline/infix