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Subject: Re: [Caml-list] camlp4 grammar and LIST1
From: Jake Donham <jake@donham.org>
To: Joel Reymont <joelr1@gmail.com>
Cc: "O'Caml Mailing List" <caml-list@yquem.inria.fr>
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X-Spam: no; 0.00; camlp:01 camlp:01 baz:01 baz:01 quux:01 quux:01 recursive:01 branching:01 10,:98 2009:98 token:01 wrote:01 caml-list:01 grammar:02 parse:02 

On Tue, Mar 10, 2009 at 3:07 PM, Joel Reymont <joelr1@gmail.com> wrote:
> I have it like this at the moment. Are you saying it won't work?

Here's an example of what I'm talking about:

  open Camlp4.PreCast
  let bar = Gram.Entry.mk "bar"
  let baz = Gram.Entry.mk "baz"
  let bar_or_baz = Gram.Entry.mk "bar_or_baz"
  ;;
  EXTEND Gram
  bar : [[ LIST0 "quux"; "bar" -> () ]];
  baz : [[ LIST0 "quux"; "baz" -> () ]];
  bar_or_baz : [[ bar | baz ]];
  END
  ;;
  Gram.parse_string bar_or_baz Loc.ghost "quux quux baz"

The given string does not parse because we've already committed to the
bar branch.

However, several variations I tried did not show this behavior (e.g.
only one quux in the string). I think there are some special cases,
although they are not documented anywhere I have found. An approach
that works for me is to think "recursive descent" and always give
rules that check at least one token before branching to another rule.

Jake