Reverse data constructor

Question

How can I define a function that will accept my type and return its primitive "synonym"? For example:

newtype MyInt = MakeInt Int

And i want a function:

unMyInt :: MakeInt -> Int

Answer 1

By pattern matching on the constructor:

unMyInt (MakeInt i) = i

Answer 2

The other (and more comfortable way sometimes) is record syntax:

newtype myInt a = MyInt { unMyInt :: Int }

This automatically defines a function

unMyInt :: MyInt -> Int