Re: FYI: default %printer/%destructor

[Hans Aberg]

On 21 Nov 2006, at 22:39, Joel E. Denny wrote:

> > But here, the LHSs should somehow be adapted to Bison notation.
>
> I think this is the key.  We can't hope to avoid collisions with every
> notation Bison might possibly want to use in the future or that users
> might already be familiar with.

The problem is that EBNF is so fundamental, it is important to find a  
good notation of it.

> There are only so many characters on the
> keyboard.

Well, Unicode has some 100000 plus characters, and one might  
substitute poor-mans-ASCII for some of them.

> Bison will have to develop its own alternatives in some cases.
> However, using () in a grammar to group symbols is pervasive in my
> experience, and so we might ought to avoid using it for other  
> purposes.

So this seems.

> I suspect that using [] in a grammar to mean optional is not nearly as
> common.

I think it is quite common, in fact.

> > I think "[ ]" will work much
> > better than "(...)?", which is sometimes used - one needs to  
> > attach actions to
> > these EBNF constructs as well, and postfix operators like "?" may  
> > cause
> > problems.
>
> I don't follow.

It might cause a long lookahead, though I do not know if it is needed  
in this case. I had to implement the implicit set notation used in a  
metamath book
  {f|P}_x
where x is the variable bound by the set construct. Then one does not  
know what variable is bound until after the "_x" subscript has been  
read, making it hard to parse f and P. So I changed it to:
  {_x f|P}

Perhaps not a problem here, as "?" will be a key symbol. Just came to  
my mind.

  Hans Aberg