---
title: Monad Transformers
author: Michael Snoyman <michael@fpcomplete.com>
description: What transformers are, why they're useful, what to be aware of
first-written: 2015-02-24
last-updated: 2015-02-24
last-reviewed: 2015-02-24
---

* Basic transformers
* Simple examples of usage
* Pitfalls of Writer laziness
* Dealing with exceptions and control structures (monad-control and exceptions packages), and losing state
* Monad transformers: [EitherT vs IO](http://stackoverflow.com/questions/25752900/exceptions-and-monad-transformers/25753497#25753497)
* https://github.com/kqr/gists/blob/master/articles/gentle-introduction-monad-transformers.md (need to get permission to relicense)