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Contents
(define-module (atbash-cipher)
#:autoload (srfi srfi-26) (cut)
#:autoload (srfi srfi-1) (iota)
#:autoload (ice-9 regex) (regexp-substitute/global
list-matches)
#:export (encode decode))
;; "zip" a...z and z...a together to create an alist of mappings.
(define alphamap
(let* ((alpha (map integer->char (iota 26 (char->integer #\a)))))
(map cons alpha (reverse alpha))))
;; Look up the given character in the alphamap and return its complement.
(define (convert-char chr)
(or (assoc-ref alphamap chr) chr))
;; Encode the given "val" string using the Atbash cipher.
(define (encode val)
(format-atbash (string-map convert-char (prepare-input val))))
;; Decode the given Atbash cipher.
(define (decode val)
(string-map convert-char (prepare-input val)))
;; Filter any unprocessable characters out of the plain text.
;; Only lowercase a-z and 0-9 are allowed.
(define (prepare-input val)
(regexp-substitute/global #f "[^a-z0-9]" (string-downcase val) 'pre "" 'post))
;; Format atbash ciphertext for output.
;; Add a space every 5 characters
;; Currently generates a preceeding space, which must be trimmed :(
(define (format-atbash val)
(string-trim
(string-concatenate
(map (compose (cut string-append " " <>)
match:substring)
(list-matches "[a-z0-9]{1,5}" val)))))
Version data entries
24 entries across 24 versions & 1 rubygems