funB = flip takeWhile primes . ( . join (*)) . flip (<=)

funB x = flip takeWhile primes ((( . join (*)) . flip (<=)) x)

funB x = takeWhile ((( . join (*)) . flip (<=)) x) primes

funB x = takeWhile (foo x) primes

foo x = (( . join (*)) . flip (<=)) x

foo x = (( . join (*)) (flip (<=) x)

foo x = flip (<=) x . join (*)

foo x = (x <=) . join (*)

-- join :: Monad m => m (m a) -> m a

-- join (*) == (**2)

foo x = (x <=) . (** 2)

foo x y = x <= (y ** 2)

isLessThanTheSquareOf = foo

funB x = takeWhile (x `isLessThanTheSquareOf`) primes

Helpful?

On Fri, Dec 19, 2014 at 2:52 PM, Magicloud Magiclouds <magicloud.magiclouds@gmail.com> wrote:

Hi,

Following code is to get a list of primes. Now it is hard for me to understand funB. I mean I can see what it does. But I cannot see the detailed process by every language part.

import Control.Monad

isPrime :: Integer -> Bool
isPrime i = ap funA funB i

funA :: Integer -> [Integer] -> Bool
funA x xs = all (\x' -> (mod x x') /= 0) xs

funB :: Integer -> [Integer]
funB = flip takeWhile primes . ( . join (*)) . flip (<=)

primes :: [Integer]
primes = 2 : filter isPrime [3, 5 ..]

main :: IO ()
main = print $ take 10 primes

--
竹密岂妨流水过
山高哪阻野云飞

And for G+, please use magiclouds#gmail.com.

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