[racket] #%top and hopeless toplevel stuff

Just an idea, every REPL interaction sexp is wrapped in
#%top-interaction, that could be how it communicates to set!, but I
don't really know.

Jay

On Wed, Aug 25, 2010 at 5:52 PM, Danny Yoo <dyoo at cs.wpi.edu> wrote:
> I wanted to make sure I understand how toplevel variables, REPLs and
> namespaces work.  I need to understand this because what I'm doing in
> WeScheme's REPL is not quite right because it doesn't match what is
> happening with DrRacket's REPL.
>
> I see that the error messages regarding toplevel variables are
> slightly different, depending on context.  e.g. set! can produce
> either the error message
>
>    set!: unbound identifier in module in: x
>
> or the message:
>
>    set!: cannot set undefined variable: x
>
> depending on the compilation context.  Furthermore, from talking with
> Carl Eastlund, I understand that interactions do something with
> namespaces when hitting toplevel variables.  The following transcript
> confirms to me that toplevel variable lookup and set! cooperates with
> namespaces, at least at the REPL:
>
>
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>> my-unbound-variable
> reference to undefined identifier: my-unbound-variable
>
>> (set! x 16)
> set!: cannot set undefined variable: x
>
>> (namespace-set-variable-value! 'my-unbound-variable "hello world")
>
>> my-unbound-variable
> "hello world"
>
>> (set! my-unbound-variable 'ok)
>
>> my-unbound-variable
> 'ok
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>
> I'm trying to understand what's happening.  How does set! know in what
> context (definitions or interactions) it is being used?  What in the
> documentation should I be looking at to better understand this?
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-- 
Jay McCarthy <jay at cs.byu.edu>
Assistant Professor / Brigham Young University
http://teammccarthy.org/jay

"The glory of God is Intelligence" - D&C 93