Well, I'm not only new to Perlmonks, but even newer to Lisp, as I just started to learn it. So, since a lot of different solutions have been posted, I thought I post my Common Lisp version (there's probably a better way to do it and I hope there isn't a bug):

  (defun roman_to_dec (roman)
    (if (not (equal roman ""))
      (let ((rtoa '((#\M . 1000)
                    (#\D . 500)
                    (#\C . 100)
                    (#\L . 50)
                    (#\X . 10)
                    (#\V . 5)
                    (#\I . 1))))
        (reduce #'(lambda (a b) (- (+ a b) (* (mod a b) 2)))
                (map 'list
                     #'(lambda (c) (cdr (assoc c rtoa)))
                     (string-upcase roman))))))
[download]

Update: Ok, the

(if (not (equal roman ""))

could probably be removed, because no error checking is necessary regarding to the description, and it is halfhearted to boot.

---

---

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:

  <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>

• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or How to display code and escape characters are good places to start.