The new primitives that you add to Guile with
(see Primitive Procedures) or with any of the other mechanisms are
placed into the module that is current when the
scm_c_define_gsubr is executed. Extensions loaded from the REPL,
for example, will be placed into the
(guile-user) module, if the
REPL module was not changed.
To define C primitives within a specific module, the simplest way is:
(define-module (foo bar)) (load-extension "foobar-c-code" "foo_bar_init")
When loaded with
(use-modules (foo bar)), the
load-extension call looks for the foobar-c-code.so (etc)
object file in Guile’s
extensiondir, which is usually a
subdirectory of the
libdir. For example, if your libdir is
extensiondir for the Guile 2.0.x
series will be /usr/lib/guile/2.0/.
The extension path includes the major and minor version of Guile (the “effective version”), because Guile guarantees compatibility within a given effective version. This allows you to install different versions of the same extension for different versions of Guile.
If the extension is not found in the
extensiondir, Guile will
also search the standard system locations, such as /usr/lib or
/usr/local/lib. It is preferable, however, to keep your extension
out of the system library path, to prevent unintended interference with
other dynamically-linked C libraries.
If someone installs your module to a non-standard location then the object file won’t be found. You can address this by inserting the install location in the foo/bar.scm file. This is convenient for the user and also guarantees the intended object is read, even if stray older or newer versions are in the loader’s path.
The usual way to specify an install location is with a
at the configure stage, for instance ‘./configure prefix=/opt’
results in library files as say /opt/lib/foobar-c-code.so.
When using Autoconf (see Introduction in The GNU
Autoconf Manual), the library location is in a
variable. Its value is intended to be expanded by
can by substituted into a source file like foo.scm.in
(define-module (foo bar)) (load-extension "XXextensiondirXX/foobar-c-code" "foo_bar_init")
with the following in a Makefile, using
(see Introduction in SED, A Stream Editor),
foo.scm: foo.scm.in sed 's|XXextensiondirXX|$(libdir)/guile/2.0|' <foo.scm.in >foo.scm
The actual pattern
XXextensiondirXX is arbitrary, it’s only something
which doesn’t otherwise occur. If several modules need the value, it
can be easier to create one foo/config.scm with a define of the
extensiondir location, and use that as required.
(define-module (foo config)) (define-public foo-config-extensiondir "XXextensiondirXX"")
Such a file might have other locations too, for instance a data
directory for auxiliary files, or
localedir if the module has
gettext message catalogue
It will be noted all of the above requires that the Scheme code to be
%load-path (see Load Paths). Presently it’s left up
to the system administrator or each user to augment that path when
installing Guile modules in non-default locations. But having reached
the Scheme code, that code should take care of hitting any of its own
private files etc.