Re: guile-vm 0.4

[Marius Vollmer]

Martin Grabmueller <address@hidden> writes:

> > From: Dirk Herrmann <address@hidden>
> > Date: Tue, 8 May 2001 16:21:16 +0200 (MEST)
> > 
> > On 11 Apr 2001, Marius Vollmer wrote:
> > 
> > > [ I just reread the "Proper Tail-Recursive" section of R5RS, and I
> > >   noticed that `eval' is required to be proper.  That is,
> > > 
> > >     (define (loop)
> > >       (eval '(loop) (current-module)))
> > >     (loop)
> > > 
> > >   is supposed to not grow the stack.  Do we want to fix that?  This
> > >   would kick out my loved `current-module' scheme...
> > > ]
> > 
> > I had kept this in my mailbox with the hope to find some time to think
> > about it.  But, unfortunately I don't seem to find the time.  Thus the
> > question:  In which way does a proper tail recursive implementation
> > conflict with the current-module scheme that guile's current module system
> > uses?
> 
> I suspect that saving/restoring the current module while evaluating
> the expression will grow the stack (or, at least the dynamic-wind
> chain), even though saving/restoring is not strictly necessary in the
> example above.

Yes, but that was a false alarm on my part.  We can keep the
save/restore semantics when implementing tail-calls to eval.  When
such a tail-call happens, we can just replace the current module
without stacking another save/restore pair on the wind-chain.  Maybe
we could make this into a general pattern that is not only available
for eval but for all uses of dynamic-wind...