Issue: PROCLAIM-LEXICAL (Version 7)

[Jon L White <jonl@lucid.com>]

re: I think the semantic implications of adding a declaration that prevents
    dynamic binding are sufficiently straightforward that we should not
    rule it out just because no one implemented it a year ago.

Of course, your right.  I was reacting to the added complication 
more recently added to permit "mixing" the D and G situations.


re: The strangeness in the current proposal is because the dynamic and
    lexical environments meet in a separate global environment.  So
    a shallow bound implementation can't just change the global cell
    when it pushes a new binding.  The shallow binding cell has to
    be a separate cell, making symbols (effectively) larger.  KMP
    and JAR suggested the use of a single cell combined with search
    for the global value if both it and the dynamic are needed.
    This is a new machanism, so we might want to think twice about
    it.

I think moon was right that the problem is really parallel to the
implementation of deep binding.  In fact, PDP10 MacLisp is "shallow
bound", but implemented the restoration stack in such a way that
it could find the toplevel value, or any intermediate value, simply
by "walking" back up that stack -- very similar to a deep-bound 
search [and such "walking" was in fact used when applying downward 
funargs].   There are numerous "cacheing" techniques to accellerate 
deep-bound searches, so I'm not making an inherent performance criticism;
rather, I fear that this is a new arena for all except perhaps ENVOS
[and Lucid's QLISP] and that simply taking on this coding task and
all its performance implications is a venture much bigger than I'd 
like to see labelled as "cleanup".


re: . . . 
    I believe this alternative (which is more or less what was proposed
    before minus all the stuff about CONSTANT proclamations, etc.) solves
    the main problems (an easily referenced global for deep bound 
    implementations and a way to establish a global variable without
    proclaiming it special and without some implementations thinking
    it's a spelling error or an omitted proclamation) and is fairly
    noncontroversial.

This is what I thought I liked about the proposal long ago.


re: In any case, I think there is a fallback better than "do nothing".

Hope so!



-- JonL --