[Jscheme-user] Re: modules?

[Timothy H. <tim...@ma...>]

On Friday, March 7, 2003, at 11:15 AM, Ken Anderson wrote:

> Some questions about modules.
>
> ? is there a way to export symbols?
Currently, everything is exported....
>  For example, in the elf/future.scm i wanted to export future, future?, 
> determined?, touch, and i wanted to have the other procedures not show 
> up in the user's environment.
>
> Rather than loading a module and seeing the exported symbols, i have to 
> explictly import it with a prefix say, "f:".
or you can import everything without a prefix ...
>  Then i either have to say
> (f:future x) or
> (define future f:future)
The current implementation allows either a prefixed importation
(environment-import "abc.scm" "f:")
or a non-prefixed import
(environment-import "abc.scm")
There is currently no way to import only a selected subset
or to export a selected subset...

Actually, you can "hack" export using set!,
The set! makes the assignment occur in the toplevel
environment and the (let () ...) hides all the other
assignments ...

> (
>   (let ()    ;;; define future, future? etc inside a let() environment
>     (define (future x) ...)
>     (define (future? x) ...)
>      ...
>     (list future future? ...))
>
>   (lambda R  ;;; use set! to lift these definitions to the global 
> environment
>     (set! future (first R))
>     (set! future? (second R))
>     ...)
> )

We could easily write a little macro which implements this style
of export:

>   (export (future future? ...)
>     (define (future x) ...)
>     (define (future? x) ...)
>     ...
>   )
>


Similarly, we could wriite a macro to import just a few values from a 
file
> (import "elf/future.scm" (future future?  ...))

which could expand to
>  (import "elf/future.scm" "HIDDEN:")
>  (define future HIDDEN:future)
>  (define future? HIDDEN:future?)
>  ...

Other variations could be implemented as well (import-all-but ....) etc.

---Tim---