Unary operators as macros

[reneha]

I stumbled over a problem when trying to define unary operators as macros.

The following example defines a macro which converts an identifier to a string:
    
    
    import macros
    
    macro M(s: untyped): string =
      result = toStrLit(s)
    
    echo M(foo)
    
    
    Run

which gives "foo" as output.

But I can't define the macro as a unary operator. If I try the following
    
    
    import macros
    
    macro `@`(s: untyped): string =
      result = toStrLit(s)
    echo @foo
    
    I get: undeclared identifier: 'foo'
    
    
    Run

I wonder what's the reason for this? Is it because there is a system-defined 
operator that gets priority? Is there a way around that?

I noticed that binary macros as operators do work, at least when the first 
argument is not **untyped**.