[Haskell-cafe] Practical introduction to monads

[yoann padioleau]

On 2 août 05, at 22:03, Paul Moore wrote:

> I've started learning Haskell, and I'm going through all the tutorial
> material I can find - there's a lot of good stuff available.
>
> One thing I haven't found a really good discussion of, is practical
> examples of building monads. There's plenty of discussion of the IO
> monad, and the state monad, and a lot of good theory on monads, but
> although I've seen tantalising statements about how powerful the
> ability to define your own monads can be, but no really concrete
> examples - something along the lines of
>
>   - here is problem X
>   - this might be our first cut at coding it
>   - we can abstract out this stuff, as a monad
>   - see how the code looks now, how much cleaner it is
>
> (I've seen this type of model developing a state monad, but I'm
> looking for a more application-specific approach).

have you read this
   http://homepages.inf.ed.ac.uk/wadler/papers/marktoberdorf/ 
marktoberdorf.pdf ?
It presents a pb, show how it sux when coded naively without monad,  
and then show
how beautiful the code is when you use a monad.

I have also one time read an example where you use monads while
implementing the unification or type inference algorithm, perhaps in  
the original
monad paper (the essence of functional programming).