[antlr-interest] new action syntax proposal

[Benjamin Niemann]

Terence Parr wrote:

> Actions are not executed during backtracking as we cannot undo
> stateful actions.  The problem is that some semantic predicates that
> test, for example, the symbol table rely on actions updating the
> symbol table during backtracking.  I propose {...} stay same as an
> action but {{...}} (double curlies) implies always execute even when
> backtracking.
> 
> Counterproposals?

I'd vote for "@always { ... }" or a similar keyword: exploit existing
syntax, use explicit keywords instead of adding more 'magic' characters.

And what about the 'undo' part? Or must the state changes be limited to
@scope stuff that can be reverted by ANTLR without user intervention?


Or did you think about stuff like "@init {{ ... }}". That would conflict
with the @always proposal. But a prefix could be used: "@always::init".
This could even be extended to

r
@always::init { change state }
@backtracking::after { revert state only in backtracking }
...
;


-- 
Benjamin Niemann
Email: pink at odahoda dot de
WWW: http://pink.odahoda.de/