Re: cond-expand and import

Dan,

Dan <[email protected]> writes:

> the (module) and (import) macros, or whatever they
> are, have never ceased to surprise me, with issues
> ranging from compilation problems to (define-macro)
> behavior inside a module.

We are waiting for the R6RS module system to rescue us.

> netcafe:~# cat >x.scm
> (module x (f)
>   (define (f x) x)
> )
>
> netcafe:~# sisc
> SISC (1.13.7)
> #;> (cond-expand (sisc (require-library 'x) (import
> x)))
> Error: import from unknown module x
>
> However,
>
> netcafe:~# sisc
> SISC (1.13.7)
> #;> (cond-expand (sisc (require-library 'x)))
> (x)
> #;> (cond-expand (sisc (import  x)))
> #;> f
> #<procedure |@x::f|>

require-library is a *function* that when *evaluated* loads the
specified library. By contrast, import is a *macro* that when *expanded*
makes the specified module bindings available. Therefore it is not
surprising that the first example doesn't work because at the time the
import happens - which is macro expansion time - the library has not
been loaded yet.

> #;> (define-syntax reqimp (syntax-rules ()
> ((_ lib)
> (begin (require-library 'lib) (import lib)))))
> #;> (reqimp x)
> Error: import from unknown module x
>
> does not work.

require-extension does the above and gets it right, e.g.

   (cond-expand (sisc (require-extension (srfi 1))))

works just fine. If you look at the implementation of require-extension
you'll see that it calls require-library at macro expansion time.


Matthias.