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Re: Modules

From: Andy Wingo
Subject: Re: Modules
Date: Sun, 30 Jan 2011 12:42:07 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.2 (gnu/linux)

Hi Neil,

On Sun 30 Jan 2011 00:17, Neil Jerram <address@hidden> writes:

> Andy Wingo <address@hidden> writes:
>> If you are using modules, they are already in one global namespace,
>> the various roots of which are in the %load-path and/or
>> %load-compiled-path.  (resolve-module '(foo bar)) should work
>> regardless of what file calls it.
> If the modules are installed, that's true.  What if they are not?

In that case you have to modify the load path, somehow.  I have been
doing this with scripts that add to $GUILE_LOAD_PATH and
$GUILE_LOAD_COMPILED_PATH.  (Which is another thing to note; if you have
an autotooled project, the .go files go in the $builddir.)

So if I'm hacking against an uninstalled tekuti, for example, I run my
code within ~/src/tekuti/env.

> For scripts that use uninstalled modules, then, some kind of solution is
> needed; ideally one that works for both 1.8 and 1.9/2.0, allows the code
> needed to live in a single common file, rather than duplicated at the
> top of each script; and continues to work if the script+module tree as a
> whole is moved to a different place in the filesystem.  Also I think
> it's preferable if the solution is a Guile one, as opposed to based on
> the #! line, or needing a shell script wrapper.

How would it look?

I guess I am unclear on the actual problem being solved here :)  Let's
consider that I am hacking on my "analysis" script, which lives at
~/src/foo/analysis.  I guess it's helping me in my "foo" project.  Now
the script gets too big; time to split into modules.  How to do that?

We have basically one option of a path to automatically add to the load
path: ~/src/foo.  It seems tractable, unless we start to consider
installing the script to /usr/bin, combined with the presence of "" in
the default load-extensions list, in which case the unexpected
interactions with other members of that path look daunting.

No, I think that the script itself will need to indicate some path to
add to the load path.

What you can do, perhaps, is add a macro:

(define-syntax add-relative-load-path
  (lambda (x)
    (syntax-case x ()
      ((_ path) (string? (syntax->datum #'path))
       (let* ((src (syntax-source #'x))
              (current-file (or (and src (assq-ref src 'filename))
                                (error "Could not determine current file 
              (vicinity (dirname (canonicalize-path current-file)))
              (path-elt (in-vicinity vicinity (syntax->datum #'path))))
         #`(eval-when (compile load eval)
             (set! %load-path (cons #,path-elt %load-path))))))))

Then in "analysis", you could `(add-relative-load-path ".")'.

But...  If you compile a .go, then install both .scm and .go somewhere,
the installed .go file will reference the build path, which was inserted
into the source via the current-file business.

(You could argue that this is precisely the case that we are _not_
interested in, given that currently we only install .go files for files
that are in the load path.  But I guess we should figure out a better
autocompilation story for files in $bindir.)

It _is_ true that we need to figure out what's going on with
(current-load-port) in 1.9, but it's not clear what to do, exactly, when
you have compiled files; you could not have the corresponding .scm at
all, or in any case when you've loaded the .go you don't actually have a
port to the .scm, and in fact if the file was loaded via
`load-from-path' you don't know exactly where the .scm is at all.

Perhaps we should residualize into the .go whether the file was compiled
for `load' or for `load-from-path', and what was the original path of
the file.

> Good point, thanks for the reminder about that.  But (for 1.9/2.0)
> `include' will always be well-defined and reliably relative to the
> containing file's name, won't it?

Yes, at expansion time.  But note the .scm/.go installation case; and
also note that the code that chooses when to use a .go over a .scm
doesn't know anything about dependencies, currently, so a change to an
included file doesn't trigger recompilation of the includer.


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