Monadic Philosophy

(Since I accidentally published part one of this series a few minutes ago, I figured I might as well start publishing the series.)

If you start learning functional programming, eventually you’ll come across the idea of a monad. Coming from the object/imperative world of languages like C#, I’ve had a hard time wrapping my head around this concept. There’s no shortage of monad tutorials out there, but most use Haskell’s IO as the prototypical example of a monad. Given that I don’t know Haskell very well, I found it hard to separate the Haskell stuff from monad stuff. So I set monads on the back burner and decided not to worry about them.

However, all that changed when Stephan Tolksdorf alerted me to his very cool monadic parser combinator library FParsec. I found the FParsec parsers much easier to read my F# parser efforts, so I became very interested in monadic parser combinators. As you might guess, a “monadic parser combinator library” makes heavy use of monads. Time to switch burners.

The problem with learning monads with FParsec is that it’s really designed for production use. I needed to break monads down to first principles, so I rolled my own monadic parser library. Make no mistake, if I were looking to build a production parser in F# right now, I’d use with FParsec. My monadic parser library might “get there” eventually, but right now it’s a toy.

Over a series of posts, I’m going to describe what I know about monads. I didn’t set out to write a tutorial on monads – as I said, there are plenty of them out there. However, I found most of the the many monad tutorials I read lacking because the did a good job explaining the “how”, but not such a good job on the “why”. Coming from an imperative world, I wanted to understand the philosophy better. That being said, there’s a lot of tutorial in and around the philosophy. Hopefully, you’ll find both useful.


It is interesting to know that you are going to blog about monads. i am curiously looking forward.
I remember having trouble with monads until I understood that monads made things quasi-imperative by taking advantage of the fact that in order to evaluate the body of a function, you have to evaluate the parameters first. So, imperative form: function1(state); function2(state); function3(state); And monadic form: function3(function2(function1(state), state), state) Something like that, anyway. The point being, in both forms function1 must execute before function2, which must execute before function3.