Sure, with whatever improvements you'd like to make.

At 23 Jan 2018 16:53:15 -0500, "John Clements" wrote:
> Permission to paste this summary on Stack Exchange?
> 
> 
> > On Jan 23, 2018, at 1:20 PM, Matthew Flatt <mfl...@cs.utah.edu> wrote:
> > 
> > At 23 Jan 2018 15:57:34 -0500, "'John Clements' via Racket Users" wrote:
> >> despite being inside of a binding of the name map
> > 
> > That's the essence of the problem. Which things are in the scope of a
> > top-level definition?
> > 
> > For example, is the reference to `f` in the scope of a binding of `f`
> > in
> > 
> >  (define (g x) (f x))
> >  (define (f x) x)
> > 
> > ?
> > 
> > How about in
> > 
> >  (begin
> >    (define (g x) (f x))
> >    (define (f x) x))
> > 
> > ? 
> > 
> > Or in 
> > 
> > (expand '(define (f x) x))
> > (define (g x) (f x))
> > 
> > or
> > 
> > (begin
> >   (expand '(define (f x) x))
> >   (define (g x) (f x)))
> > 
> > ?
> > 
> > The rule in Racket is that a top-level `define` doesn't change the
> > binding of an identifier until the `define` is evaluated. So, in
> > 
> >  (define (map x) ... map ...)
> > 
> > the reference to `map` is expanded/compiled at a point where `map`
> > refers to a module import, not a variable named `map`. By the time the
> > definition is evaluated, it's too late to redirect the meaning of `map`
> > as a reference to an import.
> > 
> > There are other choices, but I don't think there are going choices that
> > end up being significantly better or more consistent. The top level is
> > hopeless.
> > 
> > Modules behave significantly better, in part because the scope of a
> > definition is clear: from the start of the module to the end.
> > 
> >> When I try doing the same thing with a value defined in the empty program 
> >> (with the name’f’), I see the error 
> >> 
> >> define-values: assignment disallowed;
> >> cannot re-define a constant
> >>  constant: f
> >> 
> >> Which leads me to the suspicion that maybe possibly this message is 
> supposed 
> >> to be shown for the re-definition of ‘map’, as well?
> > 
> > The difference is that `f` starts out bound to the variable `f`, not to
> > an `f` import. For various reasons, we have decided that definitions
> > are allowed to shadow imports.
> > 

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