Working with MVar

In this recipe, we will look at MVar and Chan as the basic ingredients of a concurrent pipeline. We will create a Forex Order processing system, in which the orders to buy or sell currency are sent to an exchange. The exchange backend will process the orders, and print the summary.

How to do it...

1. Create a new project called working-with-mvar with the simple stack template:

        stack new working-with-mvar simple

2. Add dependencies on the containers and random libraries in the build-depends sub-section of the executable section. Also add the -threaded option to the ghc-options subsection:

        executable working-with-mvar
          hs-source-dirs:      src
          main-is:             Main.hs
          ghc-options:         -threaded
          default-language:    Haskell2010
          build-depends:       base >= 4.7 && < 5
                             , containers
                             , random

3. Open src/Main.hs. We will be adding our source here. Define...