add implode, explode and may-reverse

Add the functions implode, explode, may-reverse and
the variable *number-units-beginning*

1 files changed, 16 insertions, 0 deletions

diff --git a/cl-math.lisp b/cl-math.lisp
index a217df4..86c7a81 100644
--- a/cl-math.lisp
+++ b/cl-math.lisp
@@ -1,6 +1,8 @@
 ;;; plus one function
 ;;; it is the (next-number) and the (next-number-reversed)
 
+(defvar *number-units-beginning* nil)
+
 (defun next-digit (numerals digit)
   "Given a list of a numeral system and a digit, it returns the next digit."
   (cond
@@ -14,6 +16,20 @@
     ((zerop number) nil)
     (t (cons (mod number 10) (split-number-reversed (truncate number 10))))))
 
+(defun may-reverse (number)
+  "If units is placed on the end, reverse; else keep it."
+  (if *number-units-beginning*
+	(reverse number)
+	number))
+
+(defun explode (number)
+  "Given a number (which can have letters), it returns a list of the number"
+  (may-reverse (loop for letter across (write-to-string number) collect (intern (string letter)))))
+
+(defun implode (number)
+  "Given a list of a number (which can have letters), it returns the number"
+  (intern (apply #'concatenate 'string (mapcar #'symbol-name (may-reverse number)))))
+
 (defun next-list-number (numerals number-list-reversed)
   "Given a list of a numeral system and a list of a number, it returns a list of the next number."
   (cond