Re: [Chicken-users] How to load an extension?

[Felix]

From: Alejandro Forero Cuervo <address@hidden>
Subject: [Chicken-users] How to load an extension?
Date: Sun, 4 Jul 2010 19:19:20 +0200

> 
> If an extension called, say, 'hello' has been installed, what's the
> canonical way, with Chicken 4, to load it?

(require-extension hello)

> 
> I'm confused with require-extension, require-library, require, import,
> use and declare uses.  I'm looking for an answer that only has two
> words, the second being "hello", and two parenthesis.  I would hate to
> find out that one must use the words like "depends" to answer this
> question.

(require-extension hello)

"hello" in this case should be a normal, canonical, standard extension
library for the CHICKEN Scheme system. It's always `require-extension'
for these. When in doubt, use `require-extension'.

If the extension does not provide a module (which implies it also
doesn't provide an import library), which means it is *NOT* a normal,
canonical, standard extension library for the CHICKEN Scheme system,
then of course, it depends.

> 
> PPs: http://chicken.wiki.br/eggs%20tutorial seems confusing, it talks
> about mpeg.import.scm without specifying that it's an autogenerated
> file and it assumes that mpeg.scm uses "(module ...)", which may not
> be the case.  I'd recommend fixing that or erasing that page
> (replacing it with a link to the proper documentation that egg authors
> should use).

I will try to improve this page. All existing documentation is indeed
confusing, and everybody (including myself) gets regularly confused
about the correct way to use extensions, but that is caused by
some things that, AFAICT, can not be easily circumvented:

1. There exists an alias to `require-extension' called `use', which is
   totally equivalent, but short. I wouldn't want to remove this,
   because, lazy as I am, I try to reduce keypresses here and there,
   particularly for boilerplate forms like this.

2. CHICKEN supports static linking of extensions in a relatively
   convenient manner, something very few language implementations
   provide. Since this influences translation, compilation,
   linking/loading, extension-building and extension-installation, it
   necessarily requires some machinery (even if controlled by obscure
   command-line-options or non-standard loading/linking forms).  Note
   that you don't have to worry about this, if you are just trying to
   put together normal extensions.

3. It is also possible to link library units into a single shared
   library (that's what libchicken.so is, in the end), this and static
   linking requires all this "unit" stuff that appears in the manual.

So things are actually not that bad:

(require-extension X)/(use X) loads and imports an extension module.

(require-library X) loads an extension, but doesn't import.

(import X) imports a module, which must have been loaded somehow.

Just ignore the rest. Don't worry about static linking until you need
it. Write extensions that use `(module ...)' and all is well.


cheers,
felix