Haskell Cookbook

How to do it...

1. Create a new project combine-trans with the simple Stack template.
2. Add mtl to the build-depends subsection of the executable section:

        executable combine-trans          hs-source-dirs: src          main-is: Main.hs          default-language: Haskell2010          build-depends: base >= 4.7 && < 5                 , mtl

3. Open src/Main.hs and add the following imports after the initial module declaration. Import Prelude as well to avoid a clash with some names:

        import Prelude hiding (Either(..))        import Control.Monad.Reader        import Control.Monad.Writer        import Data.Monoid

4. Define Cursor data type to show Cursor position from top-left position of the screen:

        data Cursor = Cursor Int Int deriving Show

5. Define monoid instance for Cursor. When we combine two cursors, we simply sum ...