Re: LPeg back captures

[Sean Conner <sean@...>]

It was thus said that the Great Andrew Starks once stated:
> On Wed, Oct 23, 2013 at 10:55 PM, Andrew Starks <andrew.starks@trms.com> wrote:
> > On Wed, Oct 23, 2013 at 10:10 PM, Sean Conner <sean@conman.org> wrote:
> >>> >         DIGIT        = R"09"
> >>> >         delim_char   = P"!" -- Cb("delim")
> >>> >         flags        = P"i"
> >>> >         backref      = P"\\" * DIGIT
> >>> >         escapeddelim = P"\\" * delim_char
> >>> >         anychar      = P(1) - delim_char
> >>> >         string       = (escapeddelim + anychar)^1
> >>> >         repl         = C((string + backref)^0)
> >>> >         ere          = C((P(1) - delim_char)^0)
> >>> >         idelim_char  = Cg(P"/" + P"!" + (P(1) - (DIGIT + flags)),"delim")
> >>> >         regexp       = Ct(
> >>> >                             idelim_char
> >>> >                             * Cg(ere,"re")
> >>> >                             * delim_char
> >>> >                             * Cg(repl,"replace")
> >>> >                             * delim_char
> >>> >                             * Cg(flags^0,"flags")
> >>> >                          )
> >
> > Man... I'm sorry. I thought I was pretty sure on this. I did some
> > tests on a simpler example and I was wrong again. Order of declaration
> > doesn't matter....
> >
> >
> > ```
> > lpeg = require'lpeg'
> >
> > P, Cg, Cb, C = lpeg.P, lpeg.Cg, lpeg.Cb, lpeg.C
> >
> > the_forb_back_there = Cb("forb")
> > forb_cap = Cg(P(P"foo" + "bar"), "forb")
> >
> > main_patt = C(forb_cap * (P(1))^1 * the_forb_back_there)
> >
> > print(main_patt:match("barnillydissle"))
> > -->barnillydissle bar
> > ```
> >
> > bar is coming out as a separate return value.... I think that may be
> > the problem. I'm gonna dig more.
> 
> 
> I'm gonna work on a solution, but at least I think I know the problem:
> 
> Cb doesn't work on nested captures. So your other statements (ere,
> escapeddelim, etc) are "out of scope" with delim_char.

  I've simplified the LPeg code.  What I want is the behavior of this:

	delim  = P"/"
	field  = C((P(1) - delim)^0)
	regexp = Ct(
	               delim
	             * Cg(field,"re")
	             * delim
	             * Cg(field,"replace")
	             * delim
	             * Cg(field^-1,"flags")          
	           )

But where delim is defined as the first character of the string (instead of
the hardcoded pattern I have here).  This is harder than it looks.

  -spc