[Haskell-beginners] Monadic Project Euler 1

[Ozgur Akgun]

On 17 February 2011 21:02, Javier M Mora <jamarier at gmail.com> wrote:

> Yes, I'm trying to learn/practice Design Patterns in Haskell making euler
> problems three times:
>
> 1. Non Monad
> 2. Ad-hoc Monad
> 3. Standard Monad
>
> Thank you for help me in the 3rd Stage. I was trying to solve 2nd Stage.
> :-(
>

Sorry for jumping over one of the stages then :)

For this problem though, I can't see what the semantics of your ad-hoc monad
would be. You'll end up reimplementing a state monad, I suppose. If so, you
can always check the definition of the "standard" state monad:

http://hackage.haskell.org/packages/archive/mtl/1.1.1.1/doc/html/Control-Monad-State-Lazy.html#g:1

http://hackage.haskell.org/packages/archive/mtl/1.1.1.1/doc/html/src/Control-Monad-State-Lazy.html#State

(Disclaimer: This one is mtl-1, in mtl-2 there is no State monad. There is
the StateT monad transformer, whose Monad instance declaration might be a
bit harder to get a grasp of, and State s is a type alias to StateT s
Identity)

-- 
Ozgur Akgun
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