main =>
  S = "All human beings are born free and equal in dignity and rights.",
  println(S),
  println(caesar(S,5)),
  println(caesar(caesar(S,5),-5)),
  nl.

caesar(String, N) = Cipher =>
  Lower = [chr(I): I in 97..122],
  Upper = [chr(I): I in 65..90],
  M = create_map(Lower, Upper, N),
  % If a char is not in a..zA..z then show it as it is.
  Cipher := [M.get(C,C) : C in String].

create_map(Lower,Upper, N) = M =>
  M = new_map(),
  Len = Lower.length,
  foreach(I in 1..Len)
    II = (N+I) mod Len,
    if II == 0 then II := Len end, % Adjust for 1 based
    M.put(Upper[I],Upper[II]),
    M.put(Lower[I],Lower[II])
  end.