Defining data with functions

So far, we looked at data types that take the values of other data types (both simple or complex). Since Haskell functions are also treated as first-class values, we can also use functions in our data type definition. In this recipe, we will define two data types that use functions as one of the field.

The first data type encapsulates a function f :: a -> b, whereas the second data type is an interesting recursive structure.

Getting ready

Use the simple stack template to create a new project called data-type-with-function, and change into this directory:

    stack new data-type-with-function simple

How to do it...

1. Open src/Main.hs for editing.
2. Add a new data type Func a b to represent the function f :: a -> b:

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

3. Add a compose function. The compose function takes in two functions and  composes them together by giving an output of the first function to the next one:

       compose :: Func a b -> Func b c -> Func a c
...