Re: [Cbor] Suresh Krishnan's No Objection on draft-ietf-cbor-cddl-06: (with COMMENT)

[Carsten Bormann <[e-mail]>]

Hi Suresh,

> On Nov 21, 2018, at 15:33, Suresh Krishnan <[e-mail] <mailto:[e-mail]>> wrote:
> 
> Suresh Krishnan has entered the following ballot position for
> draft-ietf-cbor-cddl-06: No Objection
> 
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> 
> 
> ----------------------------------------------------------------------
> COMMENT:
> ----------------------------------------------------------------------
> 
> * Section 3.8.1
> 
> Looks like there is an off-by-one error here. Shouldn't
> 
> BYTES_N == 256**N
> 
> be
> 
> BYTES_N == 256**N-1

That would be correct if the line said 

   “0..BYTES_N”, where BYTES_N == 256**N-1.

But it says:

   "0...BYTES_N”, where BYTES_N == 256**N.

where “…” is the half-closed range operator that is closed on the left and open on the right, i.e., does not include the upper bound in the interval (“..” is closed on both sides and therefore does).
Please see Section 2.2.2.1 about the two range operators “..” and “…”.

(And, yes, I’m now aware that Swift uses “...” for the closed and “..<“ for the half-closed range operator (originally the latter even was “..”, the other way around from CDDL…).  Nice, but we nailed down those for CDDL quite a while ago, based on the range operators in Ruby, which are in turn somewhat, but not quite, based on those in Perl, which of course were informed by subranges in Pascal, where “..” also is a closed range.  Maybe we can add “..<“ for more visual attention in CDDL 2.0, keeping “...” to also mean half-closed.)

Grüße, Carsten

PS.: Yes, I admit I constructed the example to induce attentive readers to do a double-take, so they look up the two range operators again.  
Apparently, it kind of almost worked :-)