[r6rs-discuss] [Formal] Replacing the import's "for" syntax with implicit phasing

From: Sam TH <samth>
Date: Fri Nov 17 15:14:07 2006

On Fri, 2006-11-17 at 14:52 -0500, Abdulaziz Ghuloum wrote:

[snip]

> That is what I said, yes. Maybe the terminology got mixed up but I
> consider visiting to be evaluating the right-hand-sides of transformers
> and binding them to the keywords (plus invoking any other libraries as
> required). Since G does not use any of F's macros, none of F's macros
> (if they exist) need to be evaluated.

In this case, if define and 12 are both primitive forms (which is not
true in MzScheme, for example), then no macro-expansion must be done
before G can use the runtime values defined by F. However, if, as in
the example I gave, f is defined by a macro, then macro expansion must
take place before f can be used (or even before we can tell that f is
bound).

In general, nothing can be known about the content of a module before
the module is expanded. And a module cannot be completely expanded
before the RHSs of transformer bindings are evaluated. This process is
referred to as "visiting" in the draft.

>
> > This claim is false, as I
> > demonstrated - both expanding and visiting G require knowing the
> > bindings provided by F, which requires expansion of F.
>
> Expanding F is a separate stage from Visiting F for compiling another
> library which is in turn a different stage from invoking F for running
> another library. The fact that I assumed F is expanded and compiled is
> irrelevant as I was talking about visits (i.e. evaluating the
> transformers rhss) and invokes (i.e. evaluating the variables rhss and
> the init expressions).

If you look at section 6.2 of the draft, you will note that only two
operations on libraries are defined: visit and invoke. It is therefore
unreasonable to assume, when discussing the semantics of the draft, that
some other operation, not defined in the draft, has already been
performed.

>
> > Had F previously
> > been compiled (which you did not state), then that would not be
> > necessary.
>
> The visits and invokes as I stated them in the examples are required by
> the current draft. That is my understanding of what Section "6.2.
> Import and export phases" requires and this is what the reference
> implementations do (Andre, please correct me if I'm making assumptions
> about your implementation).

The visits and invokes are required by the draft - that much we agree
about. However, the discussion was whether they are necessary for the
correct operation of the example program you gave - which they are, but
which some of them would not be if F had previously been fully
expanded.

>
> > However, in your example, nothing has been compiled before
> > the expansion of G, so F must be expanded.
>
> I don't understand what you mean. If H imports G which imports F, then
> F must be compiled (meaning expanded, processed, whatever) before G and
> G must be compiled before H. Visiting and invoking a library are
> different from compiling it (or expanding it).

Again, visiting and invoking are the *only* operations on libraries in
the draft R6RS.

sam th
Received on Fri Nov 17 2006 - 15:13:53 UTC