;;; -*- Mode:LISP; Package:USER; Readtable:CL; Base:10 -*-

(defconst digit-letters '((0)
			  (1) (#\a #\b #\c) (#\d #\e #\f)
			  (#\g #\h #\i) (#\j #\k #\l) (#\m #\n #\o)
			  (#\p #\r #\s) (#\t #\u #\v) (#\w #\x #\y)))

; ((T U V) (M N O) (G H I) - (P R S) (D E F) (D E F) (J K L))

(defun tw (num)
  (loop for l in (cross-n (tw-explode num))
	(let ((a (make-string (length l))))
	  (loop for q in l
		for i from 0
		(setf (aref a i) q))
	  (format t "~&~a" a))))

(defun tw-explode (num)
  (loop for i below (string-length num)
	collect
	(let ((dig (aref num i)))
	  (if (and (>= dig #\0)
		   (<= dig #\9))
	      (setq dig (nth (- dig #\0) digit-letters))
	    (setq dig (list dig)))
	  dig)))

(defun cross-n (l &aux (c '(nil)))
  (loop for q in l
	(setq c (cross c q)))
  c)

(defun cross (l1 l2)
  (loop for p in l1
	append
	(loop for q in l2
	      collect (append p (list q)))))