[Joel, I added some clarifications at the bottom]
grammar(): defs() rules() epilogue(!) {
$grammar = new_grammar ($defs, $rules);
}
;
Here you won't break grammar source compatibility by omitting the ()
altogether.
%destructor(!) { printf ("A symbol was discarded.\n"); } <!>
Here, symbols with no type tags have no values but still have a
%destructor.
Of course, if no symbols in your grammar have type tags, or if you
plan to use $<tag>$ extensively for untagged symbols, it might be
reasonable to have <!> without (!) in a %destructor.
I still don't see much similarity with (!) and Then, why not having
%destructor BLOCK
implement a <*> destruction, and something like
%destructor(!) BLOCK
%destructor BLOCK %pragma(unused-value)
implement a <!> destruction? Going for the latter, of course, would
imply the possibility to do
%destructor BLOCK %pragma(unused-value) <foo>
even if foo is not untagged.
For now, this would mean having only the semantics of <*> available.
But besides debugging code, why would <!> functionality be useful?
Paolo
