Re: Proposal for new LPeg function: lpeg.Ctab()

[Sean Conner <sean@...>]

It was thus said that the Great Daurnimator once stated:
> On 14 September 2016 at 04:59, Sean Conner <sean@conman.org> wrote:
> >
> > Nothing at all what I want.  The next solution is to use a folding capture:
> >
> >         foo   = Cg(C"foo"  * EQ * C(value)) * EOL
> >         bar   = Cg(C"bar"  * EQ * C(value)) * EOL
> >         other = Cg(C(name) * EQ * C(value)) * EOL
> >
> >         list = Cf( -- FOLDING CAPTURE
> >                    Ct(Cc()) -- SEE [1]
> >                    * Cg(Cc "foo" * Cc "en")
> >                    * Cg(Cc "bar" * Cc "false")
> >                    * (foo + bar + other)^0,
> >                    function(t,n,v)
> >                      t[n] = v
> >                      return t
> >                    end
> >                  )
> >
> > It's closer to what I want, and certainly usable:
> >
> >         {
> >           bravo = "Conner",
> >           bar   = "true",
> >           alpha = "Sean",
> >           foo   = "de"
> >         }
> >
> > and yes, I can complicate the folding function to stuff the non-standard
> > headers into a sub table, but honestly, I'd rather not do that.
> 
> Hold on. This is the solution I use and I'm pretty happy with it.
> Instead of you little helper function, you can use `rawset`, which is
> a lua builtin and does exactly what you wrote (except with raw
> accesses). This is mentioned in the lpeg manual.

  It's close to what I want, but not quite there.  When parsing email [1], I
placed the defined headers at the top level of a table, and other,
non-standard headers in a sub-table named "generic" (okay, maybe not the
best name, but hey ... ).  So, a message like:

	From: <spc@conman.org>
	To: <lua-l@lists.lua.org>
	Subject: An example
	X-Non-Standard-Header: boo!

would end up being:

	{
	  from = { { address = "spc@conman.org" } }, -- a sequence because there can be multiple froms
	  to   = { { address = "lua-l@lists.lua.org" } },
	  subject = "An example",
	  generic = 
	  {
	    ['X-NON-standard-Header'] = "boo!"
	  }
	}

That way, I can interate over the non-standard headers without having to
filter out the standard headers, if that makes sense.

> Furthermore, your 'foo' and 'bar' cases are redundant.
> For clarity, I'd usually just mention them in a comment.

  For this example yes.  I did add a comment about pretending there was
additional processing since the point was there were a few fields that were
"standard."

  I don't use rawset simply because I don't really use rawset all that much
in my code.  Had I remembered it, I might have used it in the example.  But
a reason not to use rawset---either a field can only appear once and a
custom function can signal an error, or a field can repeat and I want to
keep all possible values.  

  -spc 

[1]	https://github.com/spc476/LPeg-Parsers/blob/master/email.lua