Haskell类型签名

Question

I'm having trouble understanding this type signature:

config :: Config Snap ()
config = setPort 8888 defaultConfig

Where are the -> stating the params and return type of the function? What am I missing here?

Answer 1

The -> infix type constructor takes an argument type on the left and a result type on the right. config has no parameters, and it makes no sense to write -> with nothing on the left, so the result type is the only type.

You can do the same thing with types you're more familiar with. For example:

example1 :: Int
example1 = 1

example2 :: Maybe Integer
example2 = Just 2

example3 :: [Double]
example3 = [1,2,3]

example4 :: Either String Int
example4 = Right 4

Answer 2

It's not really a function here - it's a value (well it's the configuration for snap): a Snap Config with the Snap monad and empty () additional ( other ) information sitting on it.

As you can read in the documentation it's more or less a starting point and you use the functions here to set additional informations.

So in a sense it's just the same as writing

myInt :: Int
myInt = 4