Haskell Cookbook

How to do it...

1. Use Stack to create a new project working-with-functors with the simple template:

        stack new working-with-functors simple

2. Open src/Main.hs in the editor. We will use this file to demonstrate the usage of Functors.
3. After initial module definition for Main, import the module that includes the Functor type class:

        import Data.Functor

4. Define a function to square a number. We will use it to demonstrate application of this function over several data structures:

        -- Square a number        square :: Num a => a -> a        square x = x * x

5. Functor f is a type class that needs  fmap :: (a -> b) -> f a -> f a. Data.Functor defines a function <$> synonymous to fmap. List defines an instance for Functor. We will use a square function to apply ...