• To learn Monads I've followed these steps

  1. Implement an alias of a state transformer function - see SimpleState.
  2. After that, replace the alias with a constructor and add the accessor function to apply the state transformer out of the monad - see State. Only runState needs to be exported now.
  3. Finally, create the Monad instance for State, reusing the bind and the return functions. This State monad can be used in a do block - see State.StateMonad`
  4. Implement a state monad with a transactional state inside that provides commit/rollback actions on the state - see TransactionalStateMonad.

• IMPORTANT: Monad formal definition available here

Run:

• Compile and build executables: stack build

• Compile and run all tests: stack test

• List the tests you can run individually: stack test --dry-run

• Run an individual test: stack test --test-arguments "--match=SimpleState"