Project Euler 37

trunc_prime.hs

import Data.List (nub, unfoldr)
-- FIXME
primeItr :: Integer -> Integer -> Bool
primeItr n i
  | (i * i) > n   = True
  | otherwise     = if (n `mod` i) == 0
                    then False 
                    else primeItr n (i + 1)
isPrime :: Integer -> Bool
isPrime n = primeItr n 2 -- 2-7 primes do not count (n > 10)

truncL :: Integer -> [Integer]
truncL n = nub $ map (\(k, s) -> read (drop k s)) (pairs)
  where str   = show n
        strs  = take (length str) (repeat str)
        pairs = zip [0..] strs

truncR :: Integer -> [Integer]
truncR n = unfoldr (\b -> if (b == 0) then Nothing else Just(b, b `div` 10)) n

isTruncL :: Integer -> Bool
isTruncL n = all isPrime lTruncations
  where lTruncations = truncL n

isTruncR :: Integer -> Bool
isTruncR n = all isPrime rTruncations
  where rTruncations = truncR n

isTrunc :: Integer -> Bool
isTrunc n = (isTruncR n) && (isTruncL n)