On 12/9/2015 1:41 PM, Alexis King wrote:
> On Dec 6, 2015, at 10:03 PM, George Neuner <gneun...@comcast.net> wrote:
>
> I would disagree that multiple dispatch isn't needed. The Visitor pattern is
used fairly frequently in real programs and it is just a overly complex,
error-prone way of doing double dispatch. Trying to handle more than 2 dimensions
of dispatch using Visitor involves considerable pain.
>
My understanding of the “vistor pattern” is that it’s just a way to emulate
double dispatch in a single dispatch system, so I’m not sure that’s much of a
use case. That said, I get the obvious advantages to multiple dispatch for
modeling certain classes of problems. It would be nice to support multimethods,
but I don’t think it’s currently clear how to implement multiple dispatch while
maintaining the guarantees that racket/generic has been carefully designed to
ensure.
I agree re: Visitor. My first point was that Visitor is used
extensively - proof that the need for multiple dispatch is quite
common. My other point was that Visitor doesn't scale easily to handle
dispatch on more than 2 arguments.
> On Dec 7, 2015, at 9:56 AM, brendan <bren...@cannells.com> wrote:
>
> Does the current implementation use caching? The ideal (I think) would be to
do a whole-program transformation that collects all the interface implementations.
I'm not sure if Racket even has a mechanism for that, though. Even a per-module
system would be handy, though, and that should be doable.
I’m unclear on what you’re specifically referring to here when discussing
caching, and by extension, I’m not sure what question you’re asking. It sounds
like an interesting topic, though, so I’d be curious to hear some clarification.
I *think* Brendan is referring to caching the dispatch path - i.e. once
you've determined the proper function to call for a set of arguments,
you cache the arguments (or their relevant characteristics) and the
resulting function, so if you see them again you don't need to go
through the whole dispatch process.
I've heard of this only as a research question - I've never encountered
any language implementation that actually did it.
George
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