On Wed, Sep 27, 2006 at 09:12:02PM +0000, [EMAIL PROTECTED] wrote:
> The documentation should distinguish between those that are just 
> pre-defined characters classes (E.G., <alpha> and <digit>) and 
> those that are special builtins (E.G., <before ...> and <commit>.  
> The former are things that you should be freely allowed to redefine 
> in a derived grammar, while the other second type may want to be 
> treated as reserved, or at least mention that redefining them may 
> break things in surprising ways.

FWIW, thus far in development PGE doesn't treat <before ...>
and <commit> as "special built-ins" -- they're subrules, same
as <alpha> and <digit>, that can indeed be redefined by 
derived grammars.

And I think that one could argue that redefining <alpha> or
<digit> could equally break things in surprising ways.  

I'm not arguing against the idea of special builtins or saying it's
a bad idea -- designating some named assertions as "special/non-derivable" 
could enable some really nice optimizations and implementation shortcuts  
that until now I've avoided.  I'm just indicating that I haven't
come across anything yet in the regex implementation that absolutely
requires that certain named assertions receive special treatment
in the engine.



>  -------------- Original message ----------------------
> From: "Patrick R. Michaud" <[EMAIL PROTECTED]>
> > On Wed, Sep 27, 2006 at 11:59:32AM -0700, David Brunton wrote:
> > > A quick scan of S05 reveals definitions for these seven special named 
> > assertions:
> > >   [...]
> > 
> > I don't think that <'...'> or <"..."> are really "named assertions".
> > 
> > I think that <!xyz> (as well as <+xyz> and <-xyz>) are simply special forms
> > of the named assertion <xyz>.
> > 
> > I should probably compare your list to what PGE has implemented and see if
> > there are any differences -- will do that later tonight.
> > 
> > Pm
> > 

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