On Mon, Dec 30, 2019 at 04:56:26PM +0000, Asbjørn Sloth Tønnesen wrote: > This RFC patch series is a first stab, at adding some syntactic sugar > making it more plessant to implement non-trivial dual-stack configurations, > like https://bgpfilterguide.nlnog.net/ > > I'm not completely happy with the naming at this stage, but I want to > get this series out before 36C3 ends. > > Looking forward to your feedback.
Hi
Thanks for the patchset, sorry for not giving feedback sooner, was on
vacation.
If i understand it correctly, the main point of this patchset is to
introduce 'typed symbols', which have multiple values based of network
type of processed route.
I must say that i do not like the approach taken in the patch, seems to
me that for intended purpose it is too intrusive change and the feature
is too idiosyncratic - i don't recall any language where a constant may
represent multiple unrelated values based on context. It is also
over-specific (dispatch hardcoded for net_type, while there are other,
context-specific properties, like protocol type). One way to make it less
intrusive would be to keep symbol table the same (just symbol->value
mapping) and do the change just in 'value' part.
You have this example:
define default_route:ipv4 = 0.0.0.0/0;
define default_route:ipv6 = ::/0;
This could be done by using function instead of constant:
function default_route()
{
case net.type
{
NET_IP4: return 0.0.0.0/0;
NET_IP6: return ::/0;
}
}
I agree that it is more cumbersome than your version.
Seems to me that your intended objective could be achieved, while keeping
it universal and reasonable, by several independent changes:
1) Allow 'lazy-evaluated constants', that could depend on context. These
are essentially zero-argument functions in disguise.
2) Allow something like if/case expressions (instead of just statements).
3) (optional) partially-evaluate/adapt filters based on context.
So one could wrote something like:
define default_route = case net.type {
NET_IP4: 0.0.0.0/0;
NET_IP6: ::/0;
}
(The remaining wart is a current style of enum constants, like 'NET_IP4'.)
--
Elen sila lumenn' omentielvo
Ondrej 'Santiago' Zajicek (email: santi...@crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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