Working with Traversal

In this recipe, we will work with traversals, where we can use lens for traversing many fields.

How to do it...

1. Create a new project working-with-traversal with a simple stack template.

        stack new working-with-traversal simple

2. Add a dependency on the lens library in the build-depends sub-section of the executable section. Also add containers, as we will be using Map in this recipe:

        executable working-with-traversal
         hs-source-dirs:      src
         main-is:             Main.hs
         default-language:    Haskell2010
         build-depends:       base >= 4.7 && < 5
                              , containers
                              , lens

3. Open src/Main...