Haskell Cookbook

How it works...

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

        stack new working-with-STM simple

2. Add the ghc-options subsection to the executable section. Set the option to -threaded. Also add stm to the build-depends subsection:

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

3. Open src/Main.hs. We will be adding our source here. Import Control.Concurrent.STM to importing STM module:

        module Main where

        import Control.Concurrent.STM
        import Control.Concurrent

4. Define the account type which points to TVar Int, which represents the current balance:

        newtype Account = Account (TVar Int)

5. Define ...