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module Test.Common.Rot13 (rot13) where
----------------------------------------------------------------------------
import Data.ByteString.Char8 (ByteString)
import qualified Data.ByteString.Char8 as S
import Data.Char( ord, isAsciiUpper, isAsciiLower, isAlpha, chr )
------------------------------------------------------------------------------
rotone :: Char -> Char
rotone x | acc x = f
| otherwise = x
where
aA = ord 'A'
aa = ord 'a'
xx = ord x
f = g $ if isAsciiUpper x then aA else aa
g st = chr $ st + (xx - st + 13) `mod` 26
acc c = isAlpha c && (isAsciiUpper c || isAsciiLower c)
----------------------------------------------------------------------------
rot13 :: ByteString -> ByteString
rot13 = S.map rotone
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