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    <p><em>(See also the answers at <strong><a href="https://stackoverflow.com/questions/44965/what-is-a-monad">What is a monad?</a></strong>)</em></p> <p>A good motivation to Monads is sigfpe (Dan Piponi)'s <a href="http://sigfpe.blogspot.com/2006/08/you-could-have-invented-monads-and.html" rel="nofollow noreferrer">You Could Have Invented Monads! (And Maybe You Already Have)</a>. There are <a href="http://www.haskell.org/haskellwiki/Monad_tutorials_timeline" rel="nofollow noreferrer">a LOT of other monad tutorials</a>, many of which misguidedly try to explain monads in "simple terms" using various analogies: this is the <a href="http://byorgey.wordpress.com/2009/01/12/abstraction-intuition-and-the-monad-tutorial-fallacy/" rel="nofollow noreferrer">monad tutorial fallacy</a>; avoid them.</p> <p>As DR MacIver says in <em><a href="http://www.drmaciver.com/2008/02/tell-us-why-your-language-sucks/" rel="nofollow noreferrer">Tell us why your language sucks</a></em>: <blockquote> <P> <strong>So, things I hate about Haskell:</strong> </p> <p> Let’s start with the obvious. Monad tutorials. No, not monads. Specifically the tutorials. They’re endless, overblown and dear god are they tedious. Further, I’ve never seen any convincing evidence that they actually help. Read the class definition, write some code, get over the scary name. </p></blockquote></p> <p>You say you understand the Maybe monad? Good, you're on your way. Just start using other monads and sooner or later you'll understand what monads are in general.</p> <p>[If you are mathematically oriented, you might want to ignore the dozens of tutorials and learn the definition, or follow <a href="http://lambda-the-ultimate.org/node/2455" rel="nofollow noreferrer">lectures in category theory</a> :) The main part of the definition is that a Monad M involves a "type constructor" that defines for each existing type "T" a new type "M T", and some ways for going back and forth between "regular" types and "M" types.]</p> <p>Also, surprisingly enough, one of the best introductions to monads is actually one of the early academic papers introducing monads, Philip Wadler's <a href="http://homepages.inf.ed.ac.uk/wadler/papers/marktoberdorf/baastad.pdf" rel="nofollow noreferrer">Monads for functional programming</a>. It actually has practical, <em>non-trivial</em> motivating examples, unlike many of the artificial tutorials out there.</p>
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    1. POWhat is a monad?
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    1. COThe only problem with Wadler's paper is the notation is different but I agree that the paper is pretty compelling and a clear concise motivation for applying monads.
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      1. USJared Updike
    2. CO+1 for the "monad tutorial fallacy". Tutorials on monads are akin to having several tutorials trying to explain the concept of integer numbers. One tutorial would say, "1 is similar to an apple"; another tutorial says, "2 is like a pear"; a third one says, "3 is basically an orange". But you never get the whole picture from any single tutorial. What I've taken from that is that monads are an abstract concept which can be used for many quite different purposes.
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    3. CO@stakx: Yes, true. But I didn't mean that monads are an abstraction that you cannot learn or shouldn't learn; only that it's best to learn it after you've seen enough concrete examples to perceive a single underlying abstraction. See [my other answer here](http://stackoverflow.com/questions/3261729/monad-in-non-programming-terms/3261837#3261837).
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