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case-lambda integration

From: Andy Wingo
Subject: case-lambda integration
Date: Mon, 12 Oct 2009 22:31:30 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.92 (gnu/linux)


I am climbing out of a case-lambda hole, and am wondering about
integration. If you missed the first part of this, check:

The deal is that we need case-lambda, and then some kind of
typecase-lambda to get efficient dispatch of the default generic
function protocol into the VM.

OK then, my wip-case-lambda branch is shaping up, with support for
case-lambda at the VM, debugging, assembly, GLIL, and tree-il levels. I
had to adapt psyntax too to make the new tree-il structures.

In order to expose the case-lambda functionality to Scheme though, we
need a way to make lambdas with more than one case; so I think I will
export case-lambda as an identifier by default.

That is probably uncontroversial.

But what might be is that while I was at it, I made allowances for
efficient optional and keyword argument dispatch -- so we can have
keyword arguments without consing, and arguments which are positionally
optional yet can have keywords. This is so lambda* and define* can be
implemented nicely.

There are hooks in <lambda-case> for these, but again the question is
how to expose to Scheme. As I see it there are two options:

   1. Implement lambda* (and define*) in psyntax


   2. Make the stock lambda accept #:optional, #:keyword, et al
      arguments (also a hack to psyntax)

I'm kindof leaning towards (2) actually. But I could go either way. Both
ways expose lambda* capability in the default environment -- because
psyntax boots before modules have booted, and these things need access
to psyntax internals.

Perhaps we should do (1) in the interest of interoperability; but you
still have to know you want to code portable Scheme in order to code
portable Scheme. Dunno.

Anyways, input appreciated.



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