Hi Martin,
I have a couple more minor queries/observations as I work through some
of the details of ABNF grammar:
1. For the module-stmt rule below, to be strictly correct, should it
have a comment stating that the statements in any of the "*-stmts"
blocks can appear in any order? Or is the intention that the "*-stmt"
blocks must strictly be in the order defined by the ABNF? If the latter
statement is true then does any of the text in 7.1 need to be
strengthened to explicitly state this?
module-stmt = optsep module-keyword sep identifier-arg-str
optsep
"{" stmtsep
module-header-stmts
linkage-stmts
meta-stmts
revision-stmts
body-stmts
"}" optsep
2. Similarly for import-stmt. Should this have a comment indicating
that prefix-stmt or revision-date-stmt can appear in any order?
import-stmt = import-keyword sep identifier-arg-str optsep
"{" stmtsep
prefix-stmt
[revision-date-stmt]
"}" stmtsep
On a practical note, it seems that YANG allowing various statements to
be in any arbitrary order makes writing a parser quite a lot more
complex and less efficient than writing a parser that only accepts YANG
modules that have been written in the canonical order.
Thanks,
Rob
On 14/10/2015 19:48, Robert Wilton wrote:
On 14/10/2015 18:14, Martin Bjorklund wrote:
Robert Wilton <rwil...@cisco.com> wrote:
Hi Martin,
I was looking at the YANG ABNF grammar a bit more last night (to see
how hard it would be to write a parser for it) and I had a couple more
observations. Apologies that this is after the WG last call ...
1. [Trivial] The indentation of the range statement in 9.3.5 looks
wrong.
9.3.5. Usage Example
typedef my-decimal {
type decimal64 {
fraction-digits 2;
range "1 .. 3.14 | 10 | 20..max";
}
}
I presume that it should be:
9.3.5. Usage Example
typedef my-decimal {
type decimal64 {
fraction-digits 2;
range "1 .. 3.14 | 10 | 20..max";
}
}
Fixed.
2. The description of yang-char (around page 186) doesn't seem to be
quite accurate (relative to description of legal characters in 6. YANG
Syntax), and given that it excludes character values outside the
unicode range.
Hmm, which characters are outside the unicode range?
I was thinking of anything above 0xFFFF, but it looks like my
definition (and possibly quite a few others on the Internet) of
Unicode vs UTF-16 is out of date.
;; any Unicode character including tab, carriage return, and line
;; feed, but excluding the other C0 control characters, the
surrogate
;; blocks, and the noncharacters.
yang-char = %x9 / %xA / %xD / %x20-D7FF /
...
Should this be:
;; any Unicode or IOS/IEC 10646 character including tab,
carriage return,
;; and line
;; feed, but excluding the other C0 control characters, the
surrogate
;; blocks, and the noncharacters.
yang-char = %x9 / %xA / %xD / %x20-D7FF /
I think this would be ok.
3. There are lots of comments where "these stmts can appear in any
order", e.g.
linkageStmts = ;; these stmts can appear in any order
*importStmt
*includeStmt
Am I right in interpreting that there can be any number of import and
include statements and they can be interleaved in any arbitrary
order?
Yes.
E.g. this specific example (but not in the general case) could equally
have been written *(importStmt / includeStmt).
Well, the grammar defines the canonical order. With the alternative
rule above, the canonical order would be different.
Thanks for the clarification,
Rob
/martin
.
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