to-rna.lisp

(define-condition invalid-nucleotide-error (error)
  ((nucleotide :initarg :nucleotide)))

(defvar *nuc-table*
  '((#\G . #\C) (#\C . #\G) (#\T . #\A) (#\A . #\U)))

(defun transcribe (nucleotide)
  (or (cdr (assoc nucleotide *nuc-table*))
      (error 'invalid-nucleotide-error :nucleotide nucleotide)))

(defun to-rna (string)
  (map 'string #'transcribe string))