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)))]))