Re: Parse RecDescent Nesting (Followup)

I'm doing this quickly, as I'm rushing off to the airport for a cross-US trip, but it looks like your grammar is something like:

document: chunk(s?) /\z/
chunk: open chunk close | word(s)
open: "<open>"
close: "<close>"
word: /\w+/
[download]

That should be enough to hang the proper return values from.

-- Randal L. Schwartz, Perl hacker
Be sure to read my standard disclaimer if this is a reply.

update:

document: stuff /\z/ { return $item{stuff} }
stuff: chunk(s?) { return [map {@$_} @{$item[1]} ] } # flatten adjacen
+t arrayrefs
chunk: open stuff close { return $item{stuff} } | word(s?) # returns a
+rrayref
open: "<open>"
close: "<close>"
word: /\w+/
[download]

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Re^2: Parse RecDescent Nesting (Followup) by tphyahoo (Vicar) on Jan 21, 2005 at 15:53 UTC
Thanks again Randal (for the update). The stuff to flatten the arrayrefs looks promising, and I am trying to integrate that into what I have. The updated grammar seemed dodgy to me though, because it had a circular reference -- "stuff" has "chunks", and "chunks" have "stuff". Or are circular references allowed/desirable/cool in a grammar specification? Trying to understand what this was doing made my brain swim. Best, thomas. Note: this was second reply to Randal.	[reply]
Re^3: Parse RecDescent Nesting (Followup) by merlyn (Sage) on Jan 21, 2005 at 23:55 UTC
Circular references are what permits nested open-close pairs. I wrote it the way I did so that the grammar was never ambiguous, and yet permits empty open-close pairs, or empty adjacent opens or closes. Allowing "empty" can get you into trouble in a grammar. And that fixes the problem from before. -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply]
Re^3: Parse RecDescent Nesting (Followup) by bart (Canon) on Jan 22, 2005 at 13:07 UTC
The "circular references", or, as they're more commonly known, "recursive definitions", are precisely what differentiates a grammar from a flat, regular pattern, and the thing Perl's regex-engine can't properly handle, making a parser like Parse::RecDescent useful.	[reply]