[plt-scheme] problem w/ namespace-require

--- Sam Tobin-Hochstadt <samth at ccs.neu.edu> wrote:
>   For list-related administrative tasks:
>   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
> 
> The following code produces #t when run at the (module-language)
> prompt.
> 
> (begin
>     (namespace-require '(prefix foo: mzscheme))
>     (namespace-require 'mzscheme)
>     (display (module-identifier=? (syntax +) (syntax foo:+))))
> 
> But the following module, when run in the module language, prints
> #f:
> 
> (module foo mzscheme
>     (begin
>     (namespace-require '(prefix foo: mzscheme))
>     (namespace-require 'mzscheme)
>     (display (module-identifier=? (syntax +) (syntax foo:+)))))
> 
> Why are these different, and what do I need to do to get the second
> to produce #t?

The namespace-require forms within the module affect the current
namespace--they have no effect on the module at all. The syntax forms
on the next line are given the lexical context information from the
module, where + is imported from mzscheme and foo:+ is unbound.

If you want to talk about the names bound in the *module*, try this:

  (module foo-mod mzscheme
    (require (prefix foo: mzscheme))
    (require mzscheme)
    (display (module-identifier=? (syntax +) (syntax foo:+))))

If you want to talk about the names in the current namespace, try
this:

  (module foo-ns mzscheme
    (namespace-require '(prefix foo: mzscheme))
    (namespace-require 'mzscheme)
    (display (module-identifier=? 
              (namespace-symbol->identifier '+)
              (namespace-symbol->identifier 'foo:+))))

Here I used namespace-symbol->identifier instead of syntax, because
you don't want the meaning of + and foo:+ with respect to "right
here" (which is what syntax does), but rather the meaning in the
current namespace.

Ryan



		
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