Re: Quick syncase/syntax-rules question.

["Marisha Ray & Neil Jerram" <mpriz at dircon dot co dot uk>]

From: Rob Browning <rlb@cs.utexas.edu>

>
>I'm a little confused about define-syntax and syntax-rules as
>implemented by syntax-rules.  If I say
>
>  ;; file a
>  (define-module (x a))
>  (defmacro baz () 21)
>  (export-syntax baz)
>
>  ;; file b
>  (define-module (x b))
>  (define-syntax foobar
>    (syntax-rules ()
>      ((foobar) (baz)))
>  (export-syntax foobar)
>
>and then from the guile top-level I say (use-modules (x b)) and try to
>evaluate (foobar), I get an error because baz is not defined at the
>top level.  This seems to indicate that foobar isn't recursively
>expanding baz at macroexpansion time.  Why not?


(Well I'm still testing my own understanding here, but I think ...)
Because baz in file b is an unbound variable.  There's no way for the macro
expander to know that baz may later be bound to syntax and so should be
expanded (whatever that could mean).

I guess it would work if you changed the first line of file b to
(define-module (x b) :use-module (x a)).

A third possibility: I'm not sure what happens if you say (use-modules (x
a)) at top level before (use-modules (x b)).  The export-syntax in file a
will then export baz into the guile top-level environment, but is the guile
top-level environment inherited when loading (x b)?

    Neil