Re: [Haskell-beginners] Monadic Project Euler 1

On 17/02/11 20:54, Ozgur Akgun wrote:

On 17 February 2011 19:13, Javier M Mora mailto:jamarier@gmail.com> wrote:

First Step: What I want? ------------------------

In this problem: I think monads as a DSL (Domain Specific Language)

main = do print $ sumM $ do makeList 10 -- create candidates list multiples 3 -- choose multiples of 3 multiples 5 -- choose multiples of 5 (not choosed yet)

Data under de monad is a pair of lists: (validValues, CandidatesNonValidYet)

Although my suggestion is not to use a monad for this problem, assuming this is a learning exercise, a solution using the state monad is as follows.

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. :-(

[...]

And that should be it. If you plug these all together, you'll get 33 as the answer. That is the sum of [3,6,9,5,10]. I don't know why you didn't include 10 in the list of candidates, but if that is very important you can remove it by modifying makeList.

I don't included 10 because the the original problem say multiples below X. But as you know it isn't very important.

Hope this helps.

Yes, a lot. I understand standard libraries are very well done. But they are a bit difficult to understand source code for me yet. That is the point of try very easy problems with ad-hoc Monads. Understand what problems presents Monads and how to solve.

Ozgur

Jamarier.