Re: [Haskell-cafe] Could someone help me to understand funB?

I do not think pointfree works here: Transformed to pointfree style: funB = id (fix (const (flip takeWhile primes . (. join (*)) . flip (<=)))) Optimized expression: funB = id (fix (const (flip takeWhile primes . (. join (*)) . flip (<=)))) funB = fix (const (flip takeWhile primes . (. join (*)) . flip (<=))) funB = flip takeWhile primes . (. join (*)) . flip (<=) On Sat, Dec 20, 2014 at 1:21 AM, Alex Hammel wrote:

I suspect that somebody has been abusing pointfree https://github.com/bmillwood/pointfree.

On Thu, Dec 18, 2014 at 8:35 PM, Magicloud Magiclouds < magicloud.magiclouds@gmail.com> wrote:

...

Thank you. This will take some time for me to read.

On Fri, Dec 19, 2014 at 12:32 PM, Lyndon Maydwell wrote:

...

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

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