procedure main()
ctext := caesar(ptext := map("The quick brown fox jumped over the lazy dog"))
dtext := caesar(ctext,,"decrypt")
write("Plain text  = ",image(ptext))
write("Encphered text = ",image(ctext))
write("Decphered text = ",image(dtext))
end

procedure caesar(text,k,mode)   #: mono-alphabetic shift cipher
/k := 3
k := (((k % *&lcase) + *&lcase) % *&lcase) + 1
case mode of {
  &null|"e"|"encrypt": return map(text,&lcase,(&lcase||&lcase)[k+:*&lcase])
  "d"|"decrypt"      : return map(text,(&lcase||&lcase)[k+:*&lcase],&lcase)
  }
end