Haskell Cookbook

How to do it...

1. Create a new project shopping-cart using the simple Stack template:

        stack new shopping-cart simple

2. Open shopping-cart.cabal and add a dependency on the containers library in the build-depends subsection of the executable subsection:

        executable shopping-cart
         hs-source-dirs:      src
         main-is:             Main.lhs
         default-language:    Haskell2010
         build-depends:       base >= 4.7 && < 5
                       , containers

3. Open src/Main.hs; we will add our code here. Import the module Data.Set:

        module Main where

        import Data.Set as Set

4. Create a type to represent a book. The book contains the ISBN number, title of the book, and name of the author:

        data Book = Book { isbn :: String
                 , title :: String
                 , author :: String }
                   deriving Show

5. Create the equality and ordering ...