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From: Carsten Bormann <cabo@tzi.org>
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Date: Wed, 26 Mar 2025 15:56:44 +0100
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To: Vladimir Gorej <vladimir.gorej@gmail.com>
Message-ID-Hash: 555EJXZGPMYPMQM754RR5FRDO7WPTAOP
CC: "Andrew Newton (andy)" <andy@hxr.us>,
 RFC Errata System <rfc-editor@rfc-editor.org>,
 stefan.goessner@fh-dortmund.de, glyn.normington@gmail.com,
 Orie Steele <orie@transmute.industries>, james.ietf@gmail.com,
 Tim Bray <tbray@textuality.com>, jsonpath@ietf.org
Precedence: list
Subject: =?utf-8?q?=5BJsonpath=5D_Re=3A_=5BTechnical_Errata_Reported=5D_RFC9535_=2883?=
	=?utf-8?q?43=29?=
Archived-At: 
 <https://mailarchive.ietf.org/arch/msg/jsonpath/DwLTymyyqD9wmLH5j7YIDs8lKq0>

On 2025-03-26, at 15:19, Vladimir Gorej <vladimir.gorej@gmail.com> =
wrote:
>=20
> Would something like that work for the GLOBAL errata report?

I would probably simplify this to the below.
(And Apple Mail will then destroy the alignment, sorry about that.)

Gr=C3=BC=C3=9Fe, Carsten



Original Text
-------------

;; Section 2.3.5.1
comparable          =3D literal /
                      singular-query / ; singular query value
                      function-expr    ; ValueType

;; Section 2.4
function-argument   =3D literal /
                      filter-query / ; (includes singular-query)
                      logical-expr /
                      function-expr

;; Appendix A copies these two rules into the collected ABNF.

Corrected Text
--------------

;; Section 2.3.5.1
comparable          =3D singular-query / ; singular query value
                      function-expr /  ; ValueType
                      literal

;; Section 2.4
function-argument   =3D logical-expr /
                      filter-query / ; (includes singular-query)
                      function-expr /
                      literal

;; Appendix A needs to copy these two updates in the collected ABNF.

Notes
-----

The ABNF grammars in RFC 9535 were designed to be directly usable with =
PEG (Parsing Expression Grammar) parsers.

However, PEG parsers will fail to parse $[?blt(1=3D=3D1)] or =
$[?true(1)=3D=3D0] with the grammar as given, as they employ prioritized =
choice, where the order matters.

In the order given, they will try to match the `literal` rule in =
`function-argument` with the input `1=3D=3D1`, and find that the `1` =
indeed matches a `number`, completing the match for `function-argument` =
and preempting the other choices.  The intended rest of the =
`function-argument`, `=3D=3D1` does not match anything, and the rule =
fails.
By putting the more complex `logical-expr` first, the whole `1=3D=3D1` =
matches, and the rule succeeds as intended.

Similary, the function name `true` matches as the literal `true` =
instead, and preempts parsing `true(1)` as the more complex =
`function-expr`.  Putting the `literal` choice last prevents the =
preemptive match.