On 8/4/2018 7:24 AM, Philip McGrath wrote:
On Sat, Aug 4, 2018 at 5:26 AM, George Neuner <gneun...@comcast.net
<mailto:gneun...@comcast.net>> wrote:
On Sat, 4 Aug 2018 00:08:46 -0500, Philip McGrath
<phi...@philipmcgrath.com <mailto:phi...@philipmcgrath.com>> wrote:
>and you can create a function that accepts arbitrary or
>dynamically-calculated keyword arguments (which is rarely
desirable) using
>make-keyword-procedure
But this creates a procedure that accepts anything. This seems worse
than the solution using the plist: the keyword accepting variant of
the function can't have named positional arguments.
Actually, the function passed to `make-keyword-procedure` can have
required and/or optional named positional arguments. You can use
`procedure-reduce-keyword-arity` to further specialize what arguments
the resulting function requires and/or accepts.
Ok, but it's really confusing ... the more so because there isn't a
relevant example in the docs. The signature:
(((listofkeyword?)list?)()#:restlist?. ->*.any)
doesn't readily indicate to me that additional arguments are possible.
Playing with it, it seems that the function in fact can have its own
positional arguments, but the 1st and 2nd arguments always will receive
the keyword and keyarg lists - the function's own positional arguments
(if any) must begin with the 3rd argument.
Whether this is a doc issue or an issue with my brain is a toss up. If
that empty list in the signature is meant to represent the function's
own arguments, I'd have expected some indication of that: something
like (listof name)?, or (formals*), or something instead of ().
Racket's built-in keyword argument system is fully dynamic (though
admittedly not always convenient to use dynamically out of the box),
but it also provides great support for the common case where the
keywords to be applied are statically visible, which an ad-hoc
symbols-as-"keywords" system can't.
It's the uncommon cases that are interesting. I'm going to have to play
much more with it. Thank you for the examples - I'm trying to
understand them.
George
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