At Mon, 7 Mar 2016 03:52:39 -0800 (PST), brendan wrote:
> I'm sure I'm missing something obvious here. In the Guide, introducing syntax
> objects, it says:
>
> "Most notably, free-identifier=? determines whether two identifiers refer to
> the same binding:
>
> ...
>
> (free-identifier=? #'car (let ([car 8])
> #'car))
>
> The last example above, in particular, illustrates how syntax objects
> preserve
> lexical-context information."
>
> To me it looks suspiciously like those two identifiers refer to different
> bindings.
Yep, that example is broken with the new (as of v6.3) macro system.
If we use the longhand form `(quote-syntax .... #:local)`, then the
example works as intended:
> (free-identifier=? #'car (let ([car 8])
(quote-syntax car #:local)))
#f
The problem is that #' prunes some scopes to make it better with
certain macro patterns. That scope pruning works well in a macro
implementation, but it's not so great for examples outside of a macro
implementation that are intended to probe bindings.
For more information on why #' prunes some scopes, see
http://www.cs.utah.edu/plt/scope-sets/general-macros.html#%28part._.Local_.Bindings_and_.Syntax_.Quoting%29
I'll fix the broken example in the docs.
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