A library is module declaration for use by multiple programs. Racket further groups libraries into collections. Typically, collections are added via packages (see Package Management in Racket); the package manager works outside of the Racket core, but it configures the core run-time system through collection links files.
Libraries in collections are referenced through lib paths (see require) or symbolic shorthands. For example, the following module uses the "getinfo.rkt" library module from the "setup" collection, and the "cards.rkt" library module from the "games" collection’s "cards" subcollection:
This example is more compactly and more commonly written using symbolic shorthands:
A rel-string in (lib rel-string) consists of one or more path elements that name collections, and then a final path element that names a library file; the path elements are separated by /. If rel-string contains no /s, then /main.rkt is implicitly appended to the path. If rel-string contains / but does not end with a file suffix, then .rkt is implicitly appended to the path.
Libraries also can be distributed via PLaneT packages. Such libraries are referenced through a planet module path (see require) and are downloaded by Racket on demand, instead of referenced through collections.
The most primitive collection-based modules are located in "collects" directory relative to the Racket executable. Libraries for a collection are grouped within a directory whose name matches the collection name. The path to the "collects" directory is normally included in current-library-collection-paths.
Collection-based libraries also can be installed other directories, perhaps user-specific, that are structured like the "collects" directory. Those additional directories can be included in the current-library-collection-paths parameter either dynamically, through command-line arguments to racket, or by setting the PLTCOLLECTS environment variable; see find-library-collection-paths.
Collection links files provide a mapping from top-level collection names to directories, plus additional "collects"-like directories (that have subdirectories with names that match collection names). Each collection links file to be searched is referenced by the current-library-collection-links parameter; the parameter references the file, and not the file’s content, so that changes to the file can be detected and affect later module resolution. See also find-library-collection-links.
The current-library-collection-links parameter’s value can also include hash tables that provide the same content as collection links files: a mapping from collection names in symbol form to a list of paths for the collection, or from #f to a list of "collects"-like paths.
Finally, the current-library-collection-links parameter’s value includes #f to indicate the point in the search process at which the module-name resolver should check current-library-collection-paths relative to the files and hash tables in current-library-collection-links.
To resolve a module reference rel-string, the default module name resolver searches collection links in current-library-collection-links from first to last to locate the first directory that contains rel-string, splicing a search through in current-library-collection-paths where in current-library-collection-links contains #f. The filesystem tree for each element in the link table and search path is effectively spliced together with the filesystem trees of other path elements that correspond to the same collection. Some Racket tools rely on unique resolution of module path names, so an installation and configuration should not allow multiple files to match the same collection and file combination.
The value of the current-library-collection-links parameter is initialized by the racket executable to the result of (find-library-collection-links), and the value of the current-library-collection-paths parameter is initialized to the result of (find-library-collection-paths).
Collection links files are used by collection-file-path, collection-path, and the default module name resolver to locate collections before trying the (current-library-collection-paths) search path. The collection links files to use are determined by the current-library-collection-links parameter, which is initialized to the result of find-library-collection-links.
A collection links file is read with default reader parameter settings to obtain a list. Every element of the list must be a link specification with one of the forms (list string path), (list string path regexp), (list 'root path), (list 'root path regexp), (list 'static-root path), (list 'static-root path regexp). A string names a top-level collection, in which case path is a path that can be used as the collection’s path (directly, as opposed to a subdirectory of path named by string). A 'root entry, in contrast, acts like an path in (current-library-collection-paths). A 'static-root entry is like a 'root entry, but where the immediate content of the directory is assumed not to change unless the collection links file changes. If path is a relative path, it is relative to the directory containing the collection links file. If regexp is specified in a link, then the link is used only if (regexp-match? regexp (version)) produces a true result.
A single top-level collection can have multiple links in a collection links file, and any number of 'root entries can appear. The corresponding paths are effectively spliced together, since the paths are tried in order to locate a file or sub-collection.
(find-library-collection-paths [ pre-extras post-extras]) → (listof path?) pre-extras : (listof path-string?) = null post-extras : (listof path-string?) = null
The path produced by (build-path (find-system-path 'addon-dir) (get-installation-name) "collects") is the first element of the default collection path list, unless the value of the use-user-specific-search-paths parameter is #f.
Extra directories provided in pre-extras are included next to the default collection path list, converted to complete paths relative to the executable.
If the directory specified by (find-system-path 'collects-dir) is absolute, or if it is relative (to the executable) and it exists, then it is added to the end of the default collection path list.
Extra directories provided in post-extras are included last in the default collection path list, converted to complete paths relative to the executable.
If the PLTCOLLECTS environment variable is defined, it is combined with the default list using path-list-string->path-list, as long as the value of use-user-specific-search-paths is true. If it is not defined or if the value use-user-specific-search-paths is #f, the default collection path list (as constructed by the first three bullets above) is used directly.
Note that on Unix and Mac OS X, paths are separated by :, and on Windows by ;. Also, path-list-string->path-list splices the default paths at an empty path, for example, with many Unix shells you can set PLTCOLLECTS to ":‘pwd‘", "‘pwd‘:", or "‘pwd‘" to specify search the current directory after, before, or instead of the default paths, respectively.
As long as the values of use-user-specific-search-paths and use-collection-link-paths are true, the second element in the result list is the path of the user–specific collection links file, which is (build-path (find-system-path 'addon-dir) (get-installation-name) "links.rktd").
As long as the value of use-collection-link-paths is true, the rest of the list contains the result of get-links-search-files. Typically, that function produces a list with a single path, (build-path (find-config-dir) "links.rktd").
file : path-string? collection : path-string?
(collection-file-path file collection ...+ #:fail fail-proc) → any file : path-string? collection : path-string? fail-proc : (string? . -> . any)
If file is not found, but file ends in ".rkt" and a file with the suffix ".ss" exists, then the directory of the ".ss" file is used. If file is not found and the ".rkt"/".ss" conversion does not apply, but a directory corresponding to the collections is found, then a path using the first such directory is returned.
Finally, if the collection is not found, and if fail-proc is provided, then fail-proc is applied to an error message (that does not start "collection-file-path:" or otherwise claim a source), and its result is the result of collection-file-path. If fail-proc is not provided and the collection is not found, then the exn:fail:filesystem exception is raised.
collection : path-string?
(collection-path collection ...+ #:fail fail-proc) → any collection : path-string? fail-proc : (string? . -> . any)
NOTE: This function is deprecated; use collection-file-path, instead. Collection splicing implies that a given collection can have multiple paths, such as when multiple packages provide modules for a collection.
Like collection-file-path, but without a specified file name, so that a directory indicated by collections is returned.
When multiple directories correspond to the collection, the first one found in the search sequence (see Collection Search Configuration) is returned.
→ (listof (and/c path? complete-path?)) (current-library-collection-paths paths) → void? paths : (listof (and/c path-string? complete-path?))
(listof (or/c #f (and/c path? complete-path?) (hash/c (or/c (and/c symbol? module-path?) #f) (listof (and/c path? complete-path?))))) (current-library-collection-links paths) → void?
(listof (or/c #f (and/c path-string? complete-path?) (hash/c (or/c (and/c symbol? module-path?) #f) (listof (and/c path-string? complete-path?)))))
Parameter that determines collection links files, additional paths, and the relative search order of current-library-collection-paths for finding libraries (as referenced in require, for example) through the default module name resolver and for finding paths through collection-path and collection-file-path. See Collection Search Configuration for more information.
(use-user-specific-search-paths on?) → void? on? : any/c
If -U or --no-user-path argument to racket, then use-user-specific-search-paths is initialized to #f.
If this parameter’s value is #f on start-up, then collection links files are effectively disabled permanently for the Racket process. In particular, if an empty string is provided as the -X or --collects argument to racket, then not only is current-library-collection-paths initialized to the empty list, but use-collection-link-paths is initialized to #f.