Finish reading of The Typeclassopedia

Finish reading of The Typeclassopedia from The Monad.Reader 13, but it’s just the beginning of a series of reading about papers, articles, wikibooks, blog posts, and codes, as the author said.

It’s a great article, talks about Haskell’s type class and their relationship, has plenty of very useful references.

Sieve of Eratosthenes In Haskell

Algorithm description, see Sieve of Eratosthenes

module Main where

import System.Environment

isPrime p (x:xs)
	| x*x > p	 = True
	| p `mod` x == 0 = False
	| otherwise	 = isPrime p xs

primes = 2 : oprimes
	where oprimes = 3 : [ p | p <- [5,7..], isPrime p oprimes]

main = do
	args <- getArgs
	let	n = read $ args !! 0
		x = takeWhile (< n) primes
	print $ length x
	print x

There is a HackageDB package called primes which provides an efficient lazy wheel sieve for prime generation.

This version looks nicer, but less effective:

sieve (x:xs) = x : sieve xs'
	where xs' = filter (\y -> y `mod` x /= 0) xs

primes = 2 : sieve [3,5..]

See also The Genuine Sieve of Eratosthenes