Project Euler Problem 060

import Control.Monad
import Data.Ord
import Data.List
primes :: [Integer]
primes = 2:f [3] [3,5..] where
  f (x:xs) ys = ps ++ f (xs++ps) [z | z<-qs,z`rem`x/=0] where
    (ps,qs) = span (< x*x) ys
isPrime :: Integer -> Bool
isPrime nn = imp nn primes where    
  imp n (p:ps) = if n< p*p then True
                    else if n`rem`p==0 then False
                         else imp n ps
factor :: Integer -> [Integer]
factor nn = factorimpl nn primes where
  factorimpl n pri@(p:xs) =
    if p*p>n then [n]
    else if n`rem` p == 0 then
      p:factorimpl (n `quot` p) pri
         else
           factorimpl n xs
cche :: (Show a1, Show a) => a1 -> a -> Bool
cche a b = isPrime (read(show a++show b)) && isPrime (read(show b++show a))
p60primes :: [Integer]
p60primes = takeWhile (<10000) primes
l :: [Integer]
l=p60primes
solve' :: [[Integer]]
solve' = sortBy (comparing sum ) [[a,b,c,d,e] |
          a<-l,let m=next a l,
          b<-m,let n=next b m,
          c<-n,let o=next c n,
          d<-o,let p=next d o,
          e<-p]
         where next x lst= filter (cche x) $ dropWhile (<=x) lst
p60 :: Integer
p60 = sum (head solve')
-- コンパイルして13sec
-- 26033
main :: IO ()
main = print p60