[noise] Machine-readable pattern list

Trevor Perrin trevp at trevp.net
Wed Oct 5 09:29:10 PDT 2016

On Wed, Oct 5, 2016 at 1:30 AM, Rhys Weatherley
<rhys.weatherley at gmail.com> wrote:
> On Wed, Oct 5, 2016 at 4:01 PM, Trevor Perrin <trevp at trevp.net> wrote:
>> Maybe, but if the only benefit here is that a tool that works with
>> text patterns can avoid scanning for "...", that's not that much of a
>> gain.
>> There's not that much cost to this proposal either.  But the visual
>> appearance would be a little messier (we're indicating the same
>> information 2 different ways).
> I'd argue that it is not the same information.  Pre-message tokens come from
> a more restrictive set ("e", "f", and "s" only) and can only occur in
> certain orders.  The grammar can enforce these rules if it knows early
> enough.

Sure, but in terms of the whole pattern, one of these visual
indicators is redundant (we could remove the "...", or the different
arrows, and the pre-messages would still be clear).

So that's a bit more visual clutter, and someone might wonder if the
double-arrows could be used after the dots, or single arrows before.

> I can live with it either way I suppose, but the more context-free the
> better from a langsec point of view.

Langsec is about parsing untrusted inputs, but patterns aren't
transmitted - we're just talking about a (probably small) number of
tools that might do some analysis or code-generation from patterns.

> ABNF for the grammar is appended.  Basic tokens only, no hybrid.  Extending
> it to hybrid tokens is obvious.

That's cool, but it's an easy tweak to have 2 grammars, one for
pre-messages, one without.

>> Also, currently you can think of "->" and "<-" as arrows, rather than
>> text, and I've done this sometimes:
>> https://noiseprotocol.org/docs/noise_stanford_seminar_2016.pdf
>> With "=>" notation this isn't as easy - you'd need a fat and skinny
>> arrow, or an arrow with two tails?
> Unicode has lots of arrows to choose from for fancy presentations. :-)

Yeah, but you have to choose, and the reader has to think about the difference.

I have sort of a minimalist attitude here (would prefer to leave out
any complication that doesn't add significant value), so I'm not yet
sure this is worth it.


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