; some useful constants
make "lower_a ascii "a
make "lower_z ascii "z
make "upper_a ascii "A
make "upper_z ascii "Z

; encipher a single character
to encipher_char :char :key
 local "code make "code ascii :char
 local "base make "base 0
 ifelse [and (:code >= :lower_a) (:code <= :lower_z)] [make "base :lower_a] [
     if [and (:code >= :upper_a) (:code <= :upper_z)] [make "base :upper_a] ]
 ifelse [:base > 0] [
   output char (:base + (modulo ( :code - :base + :key ) 26 ))
 ] [
   output :char
 ]
end

; encipher a whole string
to caesar_cipher :string :key
  output map [encipher_char ? :key] :string
end

; Demo
make "plaintext "|The five boxing wizards jump quickly|
make "key 3
make "ciphertext caesar_cipher :plaintext :key
make "recovered  caesar_cipher :ciphertext -:key

print sentence "| Original:| :plaintext
print sentence "|Encrypted:| :ciphertext
print sentence "|Recovered:| :recovered
bye