Can I use Scheme macro to create Perl-like statement modifiers? A
statement modifier controls execution flow at the end of an
expression. For example, instead of saying  if(condition)
{doSomthing()}, we will say doSomthing() if(condition). I was
wondering if I could implement in Scheme something similar, such as
(expression unless condition). I understand that the following code(du
stands for do-unless) works:

(define-syntax du
  (syntax-rules ()
    ((_  expression unless condition) (begin (if (not condition)
expression)))))

but what if I want to remove the "du"? I tried the following, but got
a syntax error as expected:

(define-syntax unless
  (syntax-rules ()
    ((expression _ condition) (begin (if (not conition)
expression)))))

Any suggestion?

Thanks,

On mzscheme, you can use its infix notation (described in 11.2.4) to
mimic statement modifier.

But the infix notation only affect the head, so you still have to
place the condition at the end (which differ from built-in mzscheme
condition macro).  See below for example.

HTH,
yinso