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Re: Multiple parallel environments

From: Peter Brett
Subject: Re: Multiple parallel environments
Date: Thu, 30 Jul 2009 16:19:36 +0100
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux)

address@hidden (Ludovic Courtès) writes:

> Hello!
> Peter Brett <address@hidden> writes:
>> address@hidden (Ludovic Courtès) writes:
> [...]
>>> What do you mean by "environment"?  All the global variables associated
>>> with a given file in the editor?
>> Sort of.  The whole of Guile's top level bindings at that point.  (The
>> per-directory config is literally loaded as a Scheme script, so it
>> could define and redefine functions and variables at will).
> Then you are looking for Guile's nifty first-class modules.  The module
> API is unfortunately lightly documented (info "(guile) Module System
> Reflection").

Indeed.  Should I file a feature request for "more useful
documentation of the Guile module system"?  IMHO, examples like
my use case would be very useful and informative.

How much will the way they work be changing in the next stable series
of Guile releases?  How will they work w.r.t. R6RS modules?

>>> What do you mean by "save"?  Serialize to a file the "environment"
>>> associated with a file (or the difference compared to the initial
>>> environment)?
>> It doesn't need to be serialised -- I don't even need to be able to
>> get a C pointer to it! -- it just needs to be "stashed" somewhere so
>> that I can "rewind" Guile's toplevel bindings to that point at a later
>> time.
>> Essentially, I want each directory/"project" to be able to define its
>> own functions, include its own modules etc. without stomping over
>> another project that happens to be loaded into the application at the
>> same time.
> Easy!  :-)
> What you would do is create one module for each file/project/directory:
>   (define (make-per-file-module name)
>     (let ((m (make-module)))
>       (set-module-name! m name) ;; give the module an optional name
>       (beautify-user-module! m) ;; populate the module with the
>                                 ;; default bindings
>       m))

Something like the following?

  create_module_for_dir (char *c_path) /* Path is a UTF-8 string */
    SCM magic = scm_from_locale_symbol ("*magic-dir-module*");
    SCM path  = scm_from_locale_symbol (c_path);
    SCM module = scm_resolve_module (scm_list_2 (magic, path));
    scm_remember_upto_here_2 (magic, path);
    return module;

Not entirely sure how to emulate "beautify-user-module!" in C... any ideas?

> Then you create one such module for each file/directory/etc. and somehow
> associate it with said file/directory/etc. (with an alist, a hash table,
> or something similar).  When entering a file associated with that
> module, you just have to make it current:
>   (define (enter-file-buffer file)
>     (set-current-module! (lookup-per-file-module file)))
> And voilà!  :-)
> Hope this helps,

This does help, thanks!

                               Peter :-)

Peter Brett <address@hidden>
Remote Sensing Research Group
Surrey Space Centre

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