Caesar Cypher in Haskell

caeser.hs

import Char

cCipher s = encode 3 s
cDecipher s = decode 3 s
encode sh s = map (encodeChar sh) s
decode sh s = encode (-sh) s
encodeChar sh c 
  | isChar c = shift sh c
  | otherwise = c

shift sh c = toChar (((toInt c) + sh) `mod` 74)

isChar c = (ord c >= ord '0' && ord c <= ord 'z')
toInt c = ord c - ord '0'
toChar i = chr (i + ord '0')