Haskell Cookbook

How to do it...

1. Create a new project priority-queue with the default Stack template:

        stack new priority-queue

2. Delete the src/Lib.hs file. Create a directory src/Data/ and create a new file src/Data/PriorityQueue.hs. We will add implementation of priority queue here.
3. Open priority-queue.cabal. Remove Lib from the exposed-modules subsection from the library section. Replace it with our new Data.PriorityQueue module:

        library
          hs-source-dirs:      src
          exposed-modules:     Data.PriorityQueue
          build-depends:       base >= 4.7 && < 5
          default-language:    Haskell2010

4. Open src/Data/PriorityQueue.hs. We will implement the priority queue here.

5. Add the module definition for Data.PriorityQueue:

        module Data.PriorityQueue where

6. Let's define the Queue as a sum type. ...