[Haskell-beginners] Hello (First message on the mailing list)

Olivier Revollat revollat at gmail.com
Mon Feb 10 09:56:40 UTC 2020

Hi everybody,
it's my first message on this ML :)

I don't know if it's appropriate to post this here but I would like to have
some feedback with one of my first Haskell code.
I've been inspired by a recent Numberphile video (
https://www.youtube.com/watch?v=HJ_PP5rqLg0) how explain the "Russian
Peasant" algorithm to do multiplication (here in a nutshell :

So I decided I give it a go in Haskell, here is my solution, I appreciate
if you give me some feedback on how to improve this code (make it more
"idiomatic Haskell")

NB : I apologize if it's not the right place to ask this kind of review ...
in that case, where can I post this ?

Thanks !

module DivRusse where

main :: IO ()
main = do
putStrLn "13 x 12 is"
print $ russmul 13 12

russmul :: Int -> Int -> Int
russmul a b =
let filteredPair = filter (\pair -> (fst pair) `mod` 2 /= 0 ) $ (a,b) :
russmulList a b
in foldr (\pair acc -> snd pair + acc) 0 filteredPair

russmulList :: Int -> Int -> [(Int, Int)]
russmulList 1 _ = []
russmulList a b =
let a' = a `div` 2
b' = b * 2
in (a', b') : russmulList a' b'
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