Re: [Haskell-cafe] How to dynamic plan in Haskell?

This is also an interesting solution: sums :: [[Integer]] sums = do   x <- [1..9]   go x [x] (10 - x)   where     go x xs r       | r > 0       = do         x <- [1..min x r]         go x (x:xs) (r - x)       | otherwise = return xs On 05/18/2019 02:00 AM, Magicloud Magiclouds wrote:

I see. Did not got the filterM part in mind. Thanks.

On Sat, May 18, 2019 at 1:48 PM Francesco Ariis wrote:

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Hello,

On Sat, May 18, 2019 at 12:33:00PM +0800, Magicloud Magiclouds wrote:

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I solved the question. But I could not figure out a FP style solution.

Question:

1 - 9, nine numbers. Show all the possible combinations that sum up to 10. Different orders are counted as the same. A possible solution takes advantage of powersets with the [] Monad.

λ> :m +Control.Monad λ> f cs = filterM (\x -> [True, False]) cs λ> filter ((==10) . sum) (f [1..10])

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