eval-case and toplevel prohibitions

[Andy Wingo]

Hi all,

I've been hacking at the compiler in recent days, separating out
expansion from compilation (currently they are intertwingled, which
produces some bugs), and making GHIL a more simple language, more
amenable to optimization.

I've grown to really like syncase in its psyntax.scm incarnation. (I
have something of a Dybvig adoration complex.) It has in it an eval-when
construct, but eval-when doesn't have separate rules for toplevel and
nontoplevel, just '(eval compile load):

  http://www.scheme.com/csug7/system.html#g91 (see the section on eval-when)

So I was thinking: why do we have this fetish for prohibiting certain
forms in a non-toplevel context? I am of a mind to replace eval-case
with eval-when, which is actually more expressive, as it allows us to
discriminate the different phases in non-toplevel contexts as well.

Cheers,

Andy
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