Haskell Recursion and Type Error

Question

I'm teaching myself Haskell and the best way to learn any programming language is to use it. My current "exercise" is an implementation of take. The pseudo-code is:

take(0, list) = [] --empty list
take(n, list) = const(head(list), take(n-1, tail(list))

What I've worked out in Haskell is:

myTake :: (Num a) => a -> [b] -> [b]
myTake 0 l = []
myTake n (l:ls) = l :  myTake n-1 ls

This doesn't compile when I load the file in GHCi. This is the error message I get:

Couldn't match expected type `[b]'
       against inferred type `[b1] -> [b1]'
In the second argument of `(:)', namely `myTake n - 1 ls'
In the expression: l : myTake n - 1 ls
In the definition of `myTake':
    myTake n (l : ls) = l : myTake n - 1 ls

My current Haskell resource is "Learn You a Haskell for Great Good!" and I've read the section on types several times trying to figure this out. Google has been unusually unhelpful too. I think that I don't entirely understand typing yet. Can anyone explain what's going wrong?

Answer 1

myTake n - 1 ls

is parsed like

(myTake n) - (1 ls)

because function application binds higher than any infix operator. Parenthesize it:

myTake (n - 1) ls