SRFI ?: Scheme Catalogs

This SRFI defines a file format to describe to an R6RS implementation how to find the files required for a library on a filesystem or other methods. It provides the capability of specifying different files based on the features provided by the implementation. It also provides a facility to provide meta-data about a library.

Issues

Rationale

R6RS provides a facility to define libraries. However it leaves unspecified where to find the library to load when a top level program references it. SRFI 103 attempts to codify how to find a library file on a filesystem. However, it suffers from the following limitations:

Specification

Syntax

    <catalog> --> (catalog <library>+)

    <library> --> (library <library-name> <versions> <meta>?)

    <library-name> --> Same as R6RS Libraries without versions

    <versions> --> (versions <version-info>+)

    <version-info> --> (<version-number> <features>? <url> <meta>?)

    <version-number> --> Same as R6RS version-numbers

    <features> --> (requires <feature-requirements>+)

    <feature requirement>
       --> <feature identifier>
         | (and <feature requirement>*)
         | (or <feature requirement>*)
         | (not <feature requirement>)
    
    <feature identifier> identifier

    <url> --> See RFC 3986 

    <meta> --> (@ <key-value>*)

    <key-value> --> (<name> <value>)

    <name> --> symbol

    <value> --> datum

Symantics

All scheme catalogs start with the following form:

(catalog library ...)

Libraries

Each library is in the form:

(library (versions ) (@ (name value) ...))

library-name: A R6RS library name without any version info
versions: A list of versions available
metadata (@): A list of arbitrary metadata in the form of an a-list. The name of each key-value pair must be a symbol and the value may be any datum. This specification and all future specifications for this format will not define the meanings of any metadata.

Versions

The versions of the library are in the following form:

(versions (<version-number> <requires> url (@ (name value) ...)) ...)

version-number: A list of numbers or the empty list ()
requires: the set of requirements which must be met for this library to be valid see spec
url: A valid url. This url must point to a valid resource where the library is stored. see spec
metadata (@): A list of arbitrary metadata in the form of an a-list. The name of each key-value pair must be a symbik and the value may be any type. This specification and all future specifications for this format will not define the meanings of any metadata.

Requires

A requirements clause for a particular version follows the form: (requires <requirement-clause>+)

Requirment clauses are an additional discriminator for deciding which version to use. Besides the standard R6RS descriminators of library name and version number, these additional requirements can be used for determining which source code file to use for the same version based on what features are available to the implementation.

Implementation

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The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

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