[racket] Unexpected symbol in namespace-mapped-symbols

The `!!hi.1` symbol is an "unreadable" symbol generated by macro
expansion (to avoid capturing any other identifier in a source
program). You can detect such weird symbols with `symbol-unreadable?`.

At Fri, 20 Dec 2013 20:14:30 -0200, Gustavo Massaccesi wrote:
> I'm not sure that this is a bug. I found this while using
> define-namespace-anchor.
> 
> When I run this program I get an unexpected !!hi.1 symbol in the list
> of namespace-mapped-symbols. (All the variable names begin with !! so
> they are easy to sort in  the list.)
> 
> The variable !!hi is defined inside a macro, so I expect that it
> should not be visible from the module namespace. And I can't use
> namespace-variable-value to get the value of !!hi.1 .  Also, if I
> define a "real" !!hi.1 outside the macro, then there are two !!hi.1
> symbols in the list.
> 
> Gustavo
> 
> ;-----
> #lang racket
> 
> (define-syntax-rule (define-hi)
>   (define !!hi #f))
> 
> (define-hi)
> 
> (define !!tmp #f)
> (define !!ns (variable-reference->namespace (#%variable-reference !!tmp)))
> 
> (define (symbol<? x y)
>   (string<? (symbol->string x) (symbol->string y)))
> 
> (take (sort (namespace-mapped-symbols !!ns) symbol<?) 5)
> ;==> '(!!hi.1 !!ns !!tmp #%app #%datum)
> 
> ;;;(define !!hi.1 #t)
> ;-----
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