projecteuler/60_alt.hs

{-# LANGUAGE BangPatterns #-}
import Data.List

upper = 8000

isPrime :: Int -> Bool
isPrime x = null [k | k <- [2..x-1], k * k <= x, x `mod` k == 0]

!primes = [x | x <- [2..upper], isPrime x]
    
isPrimeNew :: Int -> Bool
isPrimeNew x
    | x <= upper = elem x primes
    | otherwise = isPrime x

isPrimePair :: Int -> Int -> Bool
isPrimePair a b = isPrime(read(show a ++ show b)) && isPrime(read(show b ++ show a))

primePairs = [(a, b) | a <- primes, b <- primes, a < b, isPrimePair a b]

primeSets = [(a, b, c, d, e) | a <- primes,
                               b <- primes,
                               a < b,
                               isPrimePair b a,

                               c <- primes,
                               b < c,
                               isPrimePair c a,
                               isPrimePair c b,

                               d <- primes,
                               c < d,
                               isPrimePair d a,
                               isPrimePair d b,
                               isPrimePair d c,

                               e <- primes, 
                               d < e,
                               isPrimePair e a,
                               isPrimePair e b,
                               isPrimePair e c,
                               isPrimePair e d]


main = print $ head primeSets