Questions, loose ends, misprints, etc.

[Andre van Tonder <andre@xxxxxxxxxxxxxxxxxxx>]

Here are a few questions and possible loose ends that occurred to me 
while reading the document.  Some of these may of course only reflect 
a lack of understanding on my part:

- Can I shadow CAR from the R6RS language, either with an import 
  or a local definition?  This kind of thing is potentially useful.  
  However, the document says: "No identifier can be imported multiple 
  times...", which seems to preclude this, unless the "language" is 
  conceptually not an import?  
  
- Is "scheme://r6rs" also a library?  Specifically, can I say
  
    (import (add-prefix "scheme://r6rs" r6rs:)) 
    
- Related to previous: Does the language specification act semantically
  like an import?  It might be helpful to explain the difference, if any.  
  In particular, is "scheme://r6rs" also visited/invoked, and what do
  these mean, if anything, for the R6RS dynamic environment? 
  
- Can I import different bindings for the same identifier into different 
  phases?  I'm not sure if the document forbids this.  In fact, it
  explicitly allows the /same/ binding to be imported into different
  phases (which is also conceptually a "multiple" import).  
  I know MzScheme allows this, and it is also potentially 
  quite useful.  
  
- Is the "language" imported into all reflective levels (no matter
  how deep LET-SYNTAX is nested)?

- Would it be possible to provide a rationale for the notion of 
  indirect exports.  The thing is, I know of at least two module
  systems that do well without this notion.  I kind of see why it 
  is in there, but at the same time it kind of seems to conflict 
  (at least a little bit) with the notion of lexical scoping. 
  
- The IMPORT DSL makes me uncomfortable, since the directives do
  not seem to compose.  For example, it would be nice to compose ONLY
  and ADD-PREFIX.  
  
  However, this objection might be unfounded.  In fact, I think there is
  a misprint in the document.  Shouldn't <X-set> be <import-set> in 
  this snippet?
  
  <import-set> = <lib-path>
               | (only <X-set> <identifier>*)
               | (except <X-set> <identifier>*)
               | (add-prefix <X-set> <identifier>)
               | (rename <X-set> (<identifier> <identifier>)*)
  
- It would be more general, and would simplify the IMPORT DSL, if one could 
  specify arbitrary computations on imported identifiers.  Something like
  
          (import "scheme" (lambda (symbol)
                               (case symbol
                                 ((car) 'scheme:car)
                                 ((cdr) 'scheme:cdr)
                                 (else #f))))
                             
  from http://www.het.brown.edu/people/andre/macros/srfi-module.htm. 
  
  However, you may have other reasons for preferring a syntactic DSL.
  
- It would be nice if the toplevel could also be considered an implicit
  library.  But the no-shadowing and no-redefinition rule would
  seem to preclude this.  
  
- Can I export an unbound identifier?  For example, can I export
  literals (such as ELSE, UNQUOTE, etc.), or does this not even make
  sense.  
  
  Another potential application of this would be to make a module
  that "undefines" some bindings from "scheme://r6rs" to make a restricted
  language.  

Regards
Andre