Sieve of Eratosthenes in Haskell

sum_of_primes.hs

import Data.List
import qualified Data.Map as Map
import System.Environment (getArgs)

-- credit The Genuine Sieve of Eratosthenes (Melissa E. O’Neill)

sieve xs = sieve' xs Map.empty
sieve' [] table = []
sieve' (x:xs) table =
  case Map.lookup x table of
    Nothing -> x: sieve' xs (Map.insert (x*x) [x] table)
    Just facts -> sieve' xs (foldl' reinsert (Map.delete x table) facts)
      where reinsert table prime = Map.insertWith (++) (x+prime) [prime] table

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

-- module Main (main) where

main :: IO ()
main = do
  args <- getArgs
  let lim = case args of
            (a:_) -> read a
            _     -> 1000000
  print . sum $ takeWhile (<= lim) primes