Solution to SPOJ PRIME1 problem

SPOJ-PRIME1.hs

module Main where

import List

main :: IO ()
main = do
    noOfTestCases <- readLn
    readTestCases noOfTestCases

readTestCases :: Integer -> IO ()
readTestCases noOfTestCases = do
    if noOfTestCases > 0
        then do
            input <- getLine
            let rawLimits = map readInt $ words input
            let limits = (rawLimits !! 0, rawLimits !! 1)
            putStrLn $ concat . List.intersperse "\n" $ map show $ primesBetween limits 
            putStrLn ""
            readTestCases $ noOfTestCases-1
        else
            return ()
            
readInt :: String -> Integer
readInt i = read i :: Integer

primes = 2:3:5:7: filter isPrime [11,13..]

isPrime :: Integer -> Bool
isPrime x
    | x == 1 = False
    | x == 2 = True
    | x == 3 = True
    | not $ or [(x + 1) `mod` 6 == 0, (x - 1) `mod` 6 == 0] = False
    | otherwise = null . primeDivisors $ x
    
primeDivisors x = filter (\y -> x `mod` y == 0) 
        $ takeWhile (<= (ceiling . sqrt . fromInteger $ x)) primes 

primesBetween :: (Integer, Integer) -> [Integer]
primesBetween (n1, n2) = takeWhile (<= n2) $ dropWhile (< n1) primes