(type 2.0) -> int

    (type 2.1) -> num
    (integer? 2.0) -> #t

    1089a1090,1094
    > (xdef 'regexp regexp)
    > (xdef 'r-match regexp-match)
    > (xdef 'r-match-pos regexp-match-positions)
    > (xdef 'r-replace regexp-replace)
    > 

    arc> (= r (regexp "(-[0-9]*)+"))
    #rx"(-[0-9]*)+"
    arc> (r-match r "a-12--345b")     
    ("-12--345" "-345")

   1475 ; Lower priority ideas
   [...]
   1490 ; idea: get rid of strings and just use symbols
   1491 ; could a string be (#\a #\b . "") ?

    (def unfold (f x)
      (let res (f x)
        (if res
            (cons (car res) (unfold f (cdr res)))
            ())))

    (def romanize (i)
      (let r '((M 1000)(CM 900)(D 500)(CD 400)(C 100)(L 50)(XL 40)(X 10)(IX 9)(V 5)(IV 4)(I 1))
        (unfold 
         (fn ((i . ((r n) . rst)))
             (if (is i 0)
                   ()
                 (>= i n)
                   (cons r (cons (- i n) `((,r ,n) . ,rst)))
                   (cons "" (cons i rst))))
         (cons i r))))
    (apply string (romanize 999))