Re: Spirit Semantic actions

From: joel de guzman (isis-tech_at_[hidden])
Date: 2001-06-01 00:32:36

Hi,

Syntax:

I've been tinkering around Spirit's semantic
action syntax. I've come up with this:

    a[action]

The advantage is that we can add facilities into the 
semantic action syntax later (e.g. add attributes or other 
lazy functional tricks or a complete expression template
semantic action framework) and still maintain a clear 
separation of concerns (semantics related elements and 
possibly expressions are clearly separated inside the braces.

(I'm glad we did not commit the [] brackets for iteration :-)

Back tracking:

As was noted by Bruce Florman and originally by Larry 
Evans. There's a problem with semantic actions and back-
tracking. This happens when semantic actions are invoked 
before backtracking occurs. Additional code must be added 
to 'uncommit' a triggered semantic action of a failed parse.

The solution, it would seem, is to invoke all actions in an alternative
(or any expression that backtracks) after parsing; such that
the successful branch is already known. I am currently in search 
of a viable and seamless implementation along these lines. 

I would appreciate comments and feedback very much.

Many thanks,
Joel de Guzman