类型是什么意思？

Question

This is the newtype:

newtype Combine a b = Combine { unCombine :: (a -> b) }

I'm having problems understanding many things about this line, but the first is the braces. What are they and what do they do here - create a function from two input datatypes?

Answer 1

The braces allow for record syntax. It can be considered short-hand for the following:

newtype Combine a b = Combine (a -> b)

unCombine :: Combine a b -> (a -> b)
unCombine (Combine a) = a

Record syntax creates the unCombine function for you automatically so you don't have to define it for yourself. It comes in handy when your types have a lot of type parameters.