Haskell Cookbook

How to do it...

1. Create a new project read-trans using the simple Stack template.
2. Open read-trans.cabal and add the following dependencies in the build-depends subsection of the executable section:

        executable read-trans        hs-source-dirs: src        main-is: Main.hs        default-language: Haskell2010        build-depends: base >= 4.7 && < 5               , mtl

3. Open src/Main.hs. We will add our example over here. Import the following module after the initial module declaration:

       import Control.Monad.Reader

4. Write an example in which we keep read from an integer state, and check if our state meets certain criteria:

        example :: ReaderT Int IO ()        example = do        s <- ask        lift $ putStrLn $ "Current env state is " ++ (show s)        s_is_10 <- asks (== 10) lift $ putStrLn $ "Current state ...