>> That comes back to the point I raised initially.  With hygienic keywords, the library writers cooperate
>> to share the same keywords if they want compatibility.   I don't think it works in reality.
>> Having test: keywords to specify the predicate would be a natural choice, and we can expect multiple,
>> independently developed libraries would use it.  Do they need to cooperate _beforehand_ to share
>> the same library that exports 'test:'?  What if one library already exports 'test:', and
>> another library writer want to have the same semantics of 'test:' but doesn't want to depend on the
>> original library?

This worries me as well. Keyword arguments exist because people are not
good at long-term planning. Sharing keywords from a common library is
exactly that kind of planning.

Another thing is, people (who are not Scheme experts) will not
understand why they have to import from library C in order to use
procedures from libraries A and B. It can be acceptable for advanced
uses, but for basic stuff, I think it's far too complicated.

>> There's one obvious solution: Create a library that effectively exports all possible keywords,
>> and users of keyword arguments import them.  (It is what (gauche keyword) library in Gauche
>> does).  But then, where's hygiene?

Yes, that's like the C type system where people just use void* all over
the place so they can get work done :)

It's good to keep in mind that keyword arguments are basically a more
convenient version of passing in a record. If users have to think about
stuff like exporting identifiers every time they add a keyword argument,
that's going to be too complicated IMHO.

>> That's why I'm claiming keyword arguments isn't much about identifiers but just an extension
>> of ordinary arguments.  For positional parameters, the semantics of the first parameter differs
>> completely among procedures, but we don't think it's conflating the protocol.  It is ok that the first
>> argument of procedure f and the first argument of procedure g has completely different meanings,
>> and it's callers responsibility to pass appropriate one.  If g takes a procedure that takes filename
>> as the first argument, then it's caller's responsibility to pass such procedure to g.
>> The same applies to keyword argument.  If g takes a procedure that takes logger: argument of
>> a specific type of object, then it's caller's responsibility to pass such procedure.
>>
>
> Keyword arguments could/would make it possible to treat some procedure
> arguments in a uniform way.

Just realized that this may be useless without allow-other-keys.

If you define a procedure that can use all of its keyword arguments in a
meaningful way, then the names of those keywords shouldn't be a problem:
you know the full set of keywords when writing the procedure definition.

Hygienic keywords are useful when a keyword procedure is a wrapper for
another keyword procedure. For example, a logging wrapper that only
interprets the logging keywords, and passes all other keywords to the
procedure that is being logged without interpreting those keywords.

In that case it could be nice if the logging keyword is guaranteed
unique so it doesn't override some other logging keyword that the
wrapped procedure may be using.

But even in that case, it will be confusing to the users who have to
juggle two logging keywords. I don't see any way to do it that won't
cause confusion to some people at some point in the chain.

Maybe parameter objects are a better mechanism for all the hygienic
stuff. The logging wrapper can bind the logging parameter in the right
library instead of adding a hygienic logging keyword. People are already
used to binding parameters to variables that follow ordinary scoping and
importing rules, so the details have already been explored and are
understood.