Roman Numerals in Racket Sources

The other day, while discussing Church numerals in class, I pointed out that Racket could support Roman numeral in source programs. The essence of the idea is that, whenever an unbound identifier matches the syntax of a Roman numeral, it is automatically converted into the corresponding number. The implementation of this is here. The test client best illustrates this in action. For instance, here is a valid test case:

(define (square x) (* x x))
(check-equal? (square X) C)

The essence of the implementation is just this macro:

(define-syntax (handle-id stx)
  (syntax-case stx ()
    [(_ . any)
     (let ([str (symbol->string (syntax->datum #'any))])
       (if (roman-string? str)
           (with-syntax [(n (datum->syntax stx (roman->number str)))]
             #'(#%datum . n))
           #'(#%top . any)))]))