I'm a little rusty remembering my compilers course, but do you mean separating syntax from inflection? So that you can parse just based on a "syntax grammar" an

I'm a little rusty remembering my compilers course, but do you mean separating syntax from inflection? So that you can parse just based on a "syntax grammar" and then you can trivially assume the inflection based on where things fell in the AST? Can you explain more why this makes macros AST -> AST transformation only vacuously true? I didn't follow the argument. Also why macros require top down parsing? Perhaps more interesting, would the property you described still be called homoiconic if the the parser were context sensitive?