[gambit-list] Lexical scope

Jason E. Aten j.e.aten at gmail.com
Mon Sep 5 15:31:25 EDT 2011


One thing that helped me grok a little better lexical vs dynamic scope  is
to make a crude but perhaps useful comparison to C++:


lexical scope  <-->  tracing C++ method calls on non-virtual methods. You
can tell trace the flow of control on paper beforehand; and know what's
going to happen before running it, always.


dynamic scope <--> C++ virtual method invocation.  You don't know until
runtime which code (or variable value in the case of dynamic variables) are
being talked about, because method dispatch (and variable access in the case
of dynamic variables) depends on runtime current state.


I think dynamic variables (which are available in Common Lisp but not in
most Schemes, if I understand right) and dynamic scoping are broader in
application (a superset of) the facilities provided by C++ virtual methods,
but it's the nearest thing in a language that you more likely familiar with.


Does that help?

Experts, feel free to improve on this comparison.

- Jason


On Mon, Sep 5, 2011 at 9:51 AM, Raffael Cavallaro
<raffaelcavallaro at mac.com>wrote:

>
> On Sep 5, 2011, at 10:02 AM, Steve Graham wrote:
>
> > Can someone help?
>
> Marc's reply is, of course, succinct and correct.
>
> If you want a fuller understanding of scope, I've found the wikipedia
> article to be relatively clear and to the point:
> <http://en.wikipedia.org/wiki/Scope_(computer_science)>
>
> It covers both lexical (a.k.a. "static") scope, and dynamic scope, and
> gives examples.
>
> hth
>
> warmest regards,
>
> Ralph
>
>
> Raffael Cavallaro
> raffaelcavallaro at me.com
>
>
>
>
>
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