Re: new-model.text, please comment

[Rob Browning]

Marius Vollmer <address@hidden> writes:

> I have written down my thoughts about an evaluation model that allows
> an optimizing ahead-of-time compiler.  It's in CVS:
>
>   guile/workbook/compilation/new-model.text
>
> Please have a look and comment on it.

I've read it through once, though I need to do so again, before
commenting much, but one part wasn't completely clear to me:

> The compiler is free to reuse top-level frames for several top-level
> forms, even when executing a form will change the name/module mapping
> used in the next.  You must explicitely tell the compiler that it must
> construct a new top-level frame.  You can do this with the
> 
>   (:module-barrier)                       XXX - need better name
> 
> compiler directive.  The directive guarantees that code prior to it is
> fully executed before top-level frames for forms after it are
> constructed.  The directive must be a top-level form.

Could you provide a bit of elaboration here.  More specifically, what
does "fully executed" mean?  (I tend to start thinking of
"define-macro" when I hear that, though I guess any top-level form,
macro or not could be relevant.)  For example, does the above mean
that given the following code:

  (foo ...)
  (do-something-that-changes-the-current-module!)
  (bar ...)

the results would be undefined because the compiler is within its
rights to presume that do-something *doesn't* change the current
module unless a without a :module-barrier call like so:

  (foo ...)
  (do-something-that-changes-the-current-module!)
  (:module-barrier)
  (bar ...)

This seems to be implied by the later examples of use-modules, etc.,
but I just wanted to make sure I understood what you were stating.

-- 
Rob Browning
rlb @defaultvalue.org, @linuxdevel.com, and @debian.org
Previously @cs.utexas.edu
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