Haskell List Monad Example

Euler.hs

import Control.Monad
import Data.List
import Primes

primes4 = takeWhile (<10000) $ dropWhile (<1000) primes

result = do 
    a <- primes4
    b <- dropWhile (<= a) primes4
    guard ((sort $ show a) == (sort $ show b))
    let c = 2 * b - a
    guard (c < 10000)
    guard ((sort $ show a) == (sort $ show c))
    guard $ isPrime c primes
    return (a, b, c)

isPrime n (x:xs) = (x*x > n) || (mod n x /= 0) && (isPrime n xs)
primes = 2 : filter (\x -> isPrime x primes) [3..]

Not my code, just keeping for reference.