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beginners@haskell.org

February 2016

46 participants
23 discussions

Why does sequence (map print [1, 2, 3, 4, 5]) produce [(), (), (), (), ()] at the end?
by Olumide 03 Feb '16

03 Feb '16

Hello list, The question says it all. BTW, I'm studying LYH and I'm on the chapter on IO. The book offers and explanation but its not very clear -- to me at least. Thanks, - Olumide

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foldr on infinite list to decide prime number
by Chul-Woong Yang 03 Feb '16

03 Feb '16

Hi, all. While I know that foldr can be used on infinite list to generate infinite list, I'm having difficulty in understaind following code: isPrime n = n > 1 && -- from haskell wiki foldr (\p r -> p*p > n || ((n `rem` p) /= 0 && r)) True primes primes = 2 : filter isPrime [3,5..] primes is a infinite list of prime numbers, and isPrime does foldr to get a boolean value. What causes foldr to terminate folding? Any helps will be deeply appreciated. Thank you. Chul-Woong

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foldr with short circuit and accumulator
by Chul-Woong Yang 03 Feb '16

03 Feb '16

Hi, all. Can it be possible to do fold with short circuit and accumulator both? For example, can we find an element which is same value to adjacent one? findAdjacent [1,2..n, n, n+1, n+2.......] => n \__very long__/ Though there can be many ways to do it, Can we do it with fold[r|l]? I'll be happy to receive any comments. Chul-Woong

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