Re: r6rs libraries

[Julian Graham]

Hi Guilers,

Find attached a very early, definitely broken first draft of R6RS
library support.  I was hoping to send this before / during Libre
Planet '09, but AC outlets were scarce (and boozing at The Red Line so
much easier than hacking) so I'm attempting to send this using the
free WiFi on the Acela back to NYC.

As discussed, this version uses the following approach for mapping
Guile's module search / autoloading mechanism onto locating R6RS
libraries: When a user or a library calls `import' with an import
spec,

1. The import spec is unwrapped until an actual library reference is found.
2. If a matching library reference has already been loaded, an
interface meeting the import spec's requirements is created and
returned.
3. Otherwise, `resolve-interface' is called on the name portion of the
library reference.  If a satisficing interface cannot be loaded, the
import fails.
4. Otherwise, the import system expects that either:

   a. The loaded Guile module has registered one or more versions of a
corresponding R6RS library under the library name in the internal
library registry via the `register-library' or `register-from-path'
functions in `(ice-9 r6rs-libraries)'.  If any versions of the library
can be found in the registry, their versions are matched against the
version in the library reference as per R6RS.

   b. The loaded Guile module is a non-R6RS Guile module (e.g.,
`(guile)' or `(ice-9 syncase)').  In this case, it is wrapped in an
R6RS compatibility layer to make it accessible to the library system.

What this means is that `(ice-9 r6rs-libraries)' can automatically
load normal Guile modules, and that R6RS library expressions don't
need to be modified in order to be loadable.  It does require,
however, that every installed set of versions of an R6RS library have
a Guile module that serves as a catalog of sorts.  This catalog module
file might use `register-library' to register the entire library
expression:

(define-module (mystuff mylibrary)
  #:use-module (ice-9 r6rs-libraries))

(register-library
 '(library (mystuff mylibrary (1 2))
    (export foo)
    (import (mystuff myotherlibrary))

    (define (foo) (display "Hello, world!"))))

...or it could use the search path to register a library expression
from an external file:

(define-module (mystuff mylibrary)
  #:use-module (ice-9 r6rs-libraries))

(register-from-path "mystuff/mylibrary.scm.1")
(register-from-path "mystuff/mylibrary.scm.1.2")


This mechanism might need some tweaking, but I think it resolves some
of the issues we were discussing earlier re: users installing R6RS
libraries having to keep them separate from other Guile modules.

If anyone's interested, I've created catalog modules and library
expressions for the bits and pieces of the core set of R6RS libraries
(including `(rnrs base)') necessary for testing, and I'd be happy to
tar them up and make them available somewhere.


Some other points:

* This draft doesn't do any real validation of the `library' form.

* Phased imports for the `define-syntax' form sort of work, but there
are issues with cross-module visibility of bindings for symbols
included in the output of transformers, as discussed here [1].

* Phased imports for the `letrec-syntax' and `let-syntax' forms don't
work at all yet.


Regards,
Julian


[1] - http://lists.gnu.org/archive/html/guile-user/2009-03/msg00015.html

r6rs-libraries.scm
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