binding a partially applied function in Haskell

Question

I'm a Haskell newbie, so please excuse me if you find this question trivial:

How would I get GHCi to accept a declaration of this sort: let foo = fmap (*3) . fmap (+10)?

I tried adding a type declaration to foo (let foo :: [Int] -> [Int] = etc) to make the functor type explicit but the compiler responds Illegal Signature.

Thanks!

EDIT - Apparently there are quite a few ways to do this. I picked Tikhon's answer because his was among the first, and also fairly intuitive. Thanks, everyone!

Answer 1

To give type signatures in ghci, the best way, not requiring any extensions, is to separate the signature and the binding with a semicolon,

let foo :: Num n => [n] -> [n]; foo = map (*3) . map (+ 10)