never executed always true always false

    1 {-|
    2 Module:      Y2015.D04
    3 Description: Advent of Code Day 04 Solutions.
    4 License:     MIT
    5 Maintainer:  @tylerjl
    6 
    7 Solutions to the day 04 set of problems for <adventofcode.com>.
    8 -}
    9 module Y2015.D04
   10   ( crack
   11   ) where
   12 
   13 import Crypto.Hash.MD5 (hash)
   14 import Data.ByteString.Base16 (encode)
   15 import qualified Data.ByteString.Char8 as C
   16 
   17 -- |Cracks password hash to retrieve original value
   18 crack
   19   :: C.ByteString -- ^ Input hash
   20   -> Int -- ^ Number of leading zeroes
   21   -> Int -- ^ Original password value
   22 crack prefix d = head $ dropWhile (not . validSuffix) [0 ..]
   23   where
   24     validSuffix = check . encode . hash . (prefix <>) . C.pack . show
   25     check = (>= d) . C.length . C.takeWhile (== '0')