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Re: Featuritis: Token actions

From: Frank Heckenbach
Subject: Re: Featuritis: Token actions
Date: Thu, 24 Jul 2003 18:14:00 +0200
User-agent: semail 20030303

Hans Aberg wrote:

> If one should do such a combination, then that is perhaps that such
> immediate action tokens, when arriving, are put in a queue, until a real
> (non-action) token arrives. Then the actions of the queued tokens are
> executed when the parser discovers that the real token must be shifted onto
> the stack. That should give the right action, right?

I think so.

In fact, this might be a little better than my solution where the
action (via locations) is done when the token is reduced, because
shifting always happens in order, while reducing may not (e.g.,
`1 + 2 * 3' will reduce the `2 * 3' tokens before `1 + '). In my
code, I had to work around this problem (which wasn't too hard,
though). So this feature might be useful for me, though not

BTW, I think we'd get essentially the same power if there was a way
to stick actions to a token (independent of the token value), i.e.
basically just a way to invoke some user-defined routine when a
token is shifted. This would shift (pun intended) some work from
bison (no queue required) to the user's code -- I don't know what's
generally considered preferable ...


Frank Heckenbach, address@hidden
GnuPG and PGP keys: http://fjf.gnu.de/plan (7977168E)

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