; caesar.xom
global integer gi-k initial {13}
global stream gs-ed initial {'encode'}
global stream gs-phrase

define stream function apply-cipher (value stream phrase, value integer k, value stream ed) as
  local integer b
  local stream ciphered
  open ciphered as buffer
  repeat scan phrase
    match letter => char
      set b to char binary 0
      increment b by k when ed = 'encode'
      increment b by 26 - k when ed = 'decode'
      decrement b by 26 when char matches uc and b > 90
      decrement b by 26 when char matches lc and b > 122
      put ciphered "b" % b
    match any => char
      put ciphered char
  again
  close ciphered
  return ciphered

process
  output apply-cipher(gs-phrase, gi-k, gs-ed) || '%n%n'