[racket] Nested scope in D vs Racket

How about these two points from the referenced rationale:

1. "Allowing global symbol masking is necessary for writing good modular
code that's assembled out of separately compiled parts..."

2. "...enclosing-scope masking is useless as a modularity device..."


#1 What exactly is global symbol masking?
I have been forced to learn the options of require due to naming conflicts.
Is this global masking not being allowed?  Or are my require conflicts
problematic because my imported identifiers are coming in AT THE SAME LEVEL?
Perhaps global symbol masking says you are allowed to shadow only global
variables, but not globally.  That is, global variables can be shadowed but
only from within a nested scope.

#2 I get the impression that Racket/HtDP thinks opposite to the second
quote.  local is given a lot of detailed attention in Intermezzo 3 of
HtDP/1e, which ends by discussing nested scopes and demonstrating name
reuse.  local is important for abstraction and, due to the importance of
meaningful variable names, I would say enclosing-scope masking is very
important as a feature.  Not necessary but certainly not useless.

-Paul

> -----Original Message-----
> From: users-bounces at racket-lang.org [mailto:users-bounces at racket-lang.org]
> On Behalf Of Eduardo Cavazos
> Sent: Saturday, August 21, 2010 3:33 AM
> To: users at racket-lang.org
> Subject: [racket] Nested scope in D vs Racket
> 
> Hello,
> 
> The first example in this note is illegal in the D programming language:
> 
> http://lists.puremagic.com/pipermail/digitalmars-d/2010-August/081424.html
> 
> Coming from a Scheme background, I was surprised as this is allowed in
> Scheme. I.e. this is the quivalent code in Scheme:
> 
> (let ((a 20))
>    (let ((a 30))
>      ...))
> 
> Andrei Alexandrescu pointed out the rationale for this design decision
> here:
> 
> http://lists.puremagic.com/pipermail/digitalmars-d/2010-August/081430.html
> 
> It sounds like the D designers are "protecting" the programmers. The
> Racket team is of course concerned with the "teachability" of their
> languages and have experience with the known pitfalls in languages. So
> my question is, do any Racket people agree with the rationale provided
> by the D guys? In all your years of teaching Scheme/Racket, has this
> situation of shadowing names been a problem? (I've always seen it as a
> feature, even C supports it.)
> 
> Ed
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