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6.17.7 Load Paths
The procedure in the previous section look for Scheme code in the file system at specific location. Guile also has some procedures to search the load path for code.
- Variable: %load-path
List of directories which should be searched for Scheme modules and libraries.
%load-path
is initialized when Guile starts up to(list (%site-dir) (%library-dir) (%package-data-dir))
, prepended with the contents of theGUILE_LOAD_PATH
environment variable, if it is set. See section Configuration, Build and Installation, for more on%site-dir
and related procedures.
- Scheme Procedure: load-from-path filename
Similar to
load
, but searches for filename in the load paths. Preferentially loads a compiled version of the file, if it is available and up-to-date.
A user can extend the load path by calling add-to-load-path
.
For example, a script might include this form to add the directory that it is in to the load path:
(add-to-load-path (dirname (current-filename)))
It’s better to use add-to-load-path
than to modify
%load-path
directly, because add-to-load-path
takes care
of modifying the path both at compile-time and at run-time.
- Scheme Procedure: primitive-load-path filename [exception-on-not-found]
- C Function: scm_primitive_load_path (filename)
Search
%load-path
for the file named filename and load it into the top-level environment. If filename is a relative pathname and is not found in the list of search paths, an error is signalled. Preferentially loads a compiled version of the file, if it is available and up-to-date.By default or if exception-on-not-found is true, an exception is raised if filename is not found. If exception-on-not-found is
#f
and filename is not found, no exception is raised and#f
is returned. For compatibility with Guile 1.8 and earlier, the C function takes only one argument, which can be either a string (the file name) or an argument list.
- Scheme Procedure: %search-load-path filename
- C Function: scm_sys_search_load_path (filename)
Search
%load-path
for the file named filename, which must be readable by the current user. If filename is found in the list of paths to search or is an absolute pathname, return its full pathname. Otherwise, return#f
. Filenames may have any of the optional extensions in the%load-extensions
list;%search-load-path
will try each extension automatically.
- Variable: %load-extensions
A list of default file extensions for files containing Scheme code.
%search-load-path
tries each of these extensions when looking for a file to load. By default,%load-extensions
is bound to the list("" ".scm")
.
As mentioned above, when Guile searches the %load-path
for a
source file, it will also search the %load-compiled-path
for a
corresponding compiled file. If the compiled file is as new or newer
than the source file, it will be loaded instead of the source file,
using load-compiled
.
- Variable: %load-compiled-path
Like
%load-path
, but for compiled files. By default, this path has two entries: one for compiled files from Guile itself, and one for site packages.
When primitive-load-path
searches the %load-compiled-path
for a corresponding compiled file for a relative path it does so by
appending .go
to the relative path. For example, searching for
ice-9/popen
could find
/usr/lib/guile/2.0/ccache/ice-9/popen.go
, and use it instead of
/usr/share/guile/2.0/ice-9/popen.scm
.
If primitive-load-path
does not find a corresponding .go
file in the %load-compiled-path
, or the .go
file is out of
date, it will search for a corresponding auto-compiled file in the
fallback path, possibly creating one if one does not exist.
See section Installing Site Packages, for more on how to correctly install site packages. See section Modules and the File System, for more on the relationship between load paths and modules. See section Compiling Scheme Code, for more on the fallback path and auto-compilation.
Finally, there are a couple of helper procedures for general path manipulation.
- Scheme Procedure: parse-path path [tail]
- C Function: scm_parse_path (path, tail)
Parse path, which is expected to be a colon-separated string, into a list and return the resulting list with tail appended. If path is
#f
, tail is returned.
- Scheme Procedure: search-path path filename [extensions [require-exts?]]
- C Function: scm_search_path (path, filename, rest)
Search path for a directory containing a file named filename. The file must be readable, and not a directory. If we find one, return its full filename; otherwise, return
#f
. If filename is absolute, return it unchanged. If given, extensions is a list of strings; for each directory in path, we search for filename concatenated with each extension. If require-exts? is true, require that the returned file name have one of the given extensions; if require-exts? is not given, it defaults to#f
.For compatibility with Guile 1.8 and earlier, the C function takes only three arguments.
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