Title

Author

Status

• Received: 2008/03/25
• Draft: 2008/03/25 - 2008/05/24
• Revised: 2008/07/22
• Draft extended: 2008/07/22 - 2008/08/22
• Revised: 2008/12/22

Table of contents

• Abstract
• Rationale
• Specification
• Referencing SRFI Libraries
• Naming convention
• Included SRFIs
• Omitted SRFIs
• Withdrawn SRFIs
• Future SRFIs
• Existing SRFIs and R⁶RS
• Relation to SRFIs 0 and 7
• Implementation
• Acknowledgments
• References
• Copyright

Abstract

Over the past ten years, numerous libraries have been specified via the Scheme Requests for Implementation process. Yet until the recent ratification of the Revised⁶ Report on the Algorithmic Language Scheme, there has been no standardized way of distributing or relying upon library code. Now that such a library system exists, there is a real need to organize these existing SRFI libraries so that they can be portably referenced.

This SRFI is designed to facilitate the writing and distribution of code that relies on SRFI libraries. It identifies a subset of existing SRFIs that specify features amenable to provision (and possibly implementation) as libraries (SRFI Libraries) and proposes a naming convention for this subset so that these libraries may be referred to by name or by number.

Rationale

With the advent of R⁶RS, it has become possible to write and distribute portable Scheme code as libraries. However, there is no agreed upon way to refer to SRFI libraries, leaving implementors to create their own conventions thus thwarting portability of code which relies on SRFIs. So there is an immediate and obvious need for standardized SRFI library names.

The naming convention proposed in this document enjoys the following properties:

1. it fully conforms with the R⁶RS library reference syntax,
2. it is consistent with the naming convention employed by R⁶RS Standard Libraries,
3. it is based on SRFI numbers so that names for libraries can be chosen simply and without conflict,
4. it allows (optional) mnemonic based references for readability and sub-libraries,
5. it ensures uniqueness of names over time,
6. it avoids the need for a naming authority,
7. and it represents a consensus among several Scheme implementors at the time.

Specification

This specification includes the following: a library referencing scheme for all past and future SRFI libraries, a naming convention for selecting library names, and enumeration of library names selected for all currently finalized SRFIs that specify libraries.

Although R⁶RS's notion of a library is the one used here, this SRFI attempts to minimize assumptions made about a Scheme system's conformance to R⁶RS so that systems may support SRFI Libraries without needing to support all of the R⁶RS library system. In particular, the for clause is not needed for any existing SRFI Library, and versioning information is not used. This is important for systems such as ERR⁵RS, which do not support these features.

Referencing SRFI Libraries

The purpose of this SRFI is to name SRFI libraries in a consistent and uniform manner, both in the case of existing SRFIs and in the case of SRFIs yet to be written.

A SRFI library reference consists of two required components:

• the identifier srfi,
• and the SRFI number, represented as the identifier :n.

Discussion: Several current Scheme implementations supporting SRFIs use names consisting of srfi and the relevant SRFI number. For example, Larceny, PLT Scheme, Scheme 48 all do. Use of these components also has precedents in SRFIs 0 and 7.

Discussion: Since this SRFI is only concerned with the naming of SRFI libraries, the srfi prefix is included to clearly distinguish it as a SRFI reference, and the number component is included to disambiguate among SRFIs, while allowing for simple naming without clashes or authorities. During the discussion period, it was made clear some would prefer libraries not be distinguished as SRFIs and that names be strictly mnemonic. Such a requirement broadens the scope of this proposal from a convention for SRFI libraries to the more general case of Scheme libraries and poses a much more difficult problem to solve. Instead, the particular problem is solved in such a way as to hopefully not interfere with future more general naming conventions.

Additionally, a SRFI library reference consists of one or more optional mnemonic components following the naming convention described below.

A SRFI library reference has the following form,

(srfi :<uinteger 10> <identifier> ...),

Discussion: The colon (:) prefix is used in order to make the SRFI number component an identifier, as required by R⁶RS. Several Scheme implementors expressed the importance of R⁶RS conformance and supported the colon prefix as a reasonable, if somewhat arbitrary, way to render the number as an identifier. The issue of mapping library references to file paths is left completely unspecified by this SRFI and R⁶RS.

(srfi :1),

(srfi :1 lists).

Discussion: Even though the latter uses a library name, the SRFI number must still be supplied. This is done to ensure fairness and uniqueness—a SRFI should not be able to prevent other SRFIs from using the same name, but at the same time, SRFI library references should remain unambiguous.

Discussion: Since the number-only naming scheme ensures both uniqueness and fairness, the named-library scheme is redundant, but it is included to make library imports more readable. Although the same could be achieved via a comment, comments are not checked. The named-library scheme can thus be used to increase the likelihood that the correct library is imported.

The remaining identifier subforms are used to name sublibraries within a SRFI Library. For example, SRFI 41, Streams, defines primitive and derived libraries within the streams library. These can be referenced as

(srfi :41 streams primitive),
(srfi :41 streams derived).

Naming convention

Mnemonic library names are chosen according to the following conventions: Libraries that define datatypes are typically pluralized (e.g., arrays, basic-string-ports). Libraries that provide new expression forms are named by the name of their new form (e.g., let-values, rec, and-let*). Libraries that define a single procedure (or that have a primary procedure) are given the name of the procedure (e.g., error, cat). Libraries that provide a large API of syntaxes and values are named in a descriptive manner derived from their title (e.g., lightweight-testing, real-time-multithreading). This naming convention is consistent with the names chosen in the R⁶RS Standard Libraries.

Discussion: Some authors specified names that should be used for libraries. These names are not used here. Instead, a consistent naming scheme is used that happens to differ from the authors' originally chosen names.

Discussion: There is opportunity for grouping related SRFIs together. For example, SRFI 28, Basic Format Strings, and SRFI 48, Intermediate Format Strings, could be grouped into a common format library with simple and intermediate components. This has been avoided, preferring instead to follow a one SRFI, one (top-level) library convention. Although within a single SRFI, several sub-libraries can be defined, thus achieving grouping. This simplifies the naming convention and prevents the need for a naming authority which decides what shall and shall not be grouped together. Instead, grouping must be achieved by the SRFI process, as it should.

Included SRFIs

The criterion for inclusion in the set of SRFI Libraries is that the finalized SRFI only specify a set of bindings which can be provided as a library. SRFI Libraries need not be implementable as an R⁶RS library, but they must specify an interface which could be used as if it were. This means, for example, that lexical syntax extensions cannot be a part of a SRFI Library. SRFIs that specify global semantic changes to Scheme also cannot be SRFI Libraries. For example, a Lazy Scheme SRFI or a SRFI that fixed order of evaluation in procedure application could not be a SRFI Library because these features cannot be provided as a set of bindings.

Some SRFIs specify alternative semantics to standard Scheme bindings. In some cases, such as SRFI 5's let, it's clear that making the alternative binding for let available as a library binding is desirable. Authors that wish to use SRFI 5's let, rather than R⁶RS's let, simply import the SRFI 5 binding and exclude the R⁶RS binding for let (or rename to avoid the clash).

Other SRFIs, however, define alternative bindings that are intended to be used throughout a Scheme system. For example, SRFI 63's equal? and most of SRFI 70, Numbers, are defined like this. But if the author intends for these bindings to replace the standard bindings, then there is no way of making this feature available as a library, so the SRFI cannot be a SRFI Library.

The approach taken in this SRFI is that a SRFI is excluded as a SRFI Library if it explicitly states the binding is to replace the standard one. For example, SRFI 70, Numbers, is excluded because it explicitly revises the text of R⁵RS, thus intending to make a global semantic change to the language which cannot be provided as a library. On the other hand, SRFI 63, Homogeneous and Heterogeneous Arrays, is included and provides a binding for equal? because the SRFI 63 document does not explicitly state this should replace the standard equal? binding.

The following SRFI library names are defined:

Omitted SRFIs

SRFIs are not libraries, they are requests for features. Thus, several SRFIs specify features which cannot be provided as a library and those SRFIs are intentionally omitted here. For example, SRFIs which specify extensions to concrete syntax or extensions to the semantics of top-level programs cannot be provided as libraries and are therefore omitted from this SRFI. The following table lists omitted (finalized) SRFIs and the reason for their omission.

SRFI	Title	Reason for omission
0	Feature-based conditional expansion construct	Modifies semantics of top-level programs.
4	Homogeneous numeric vector datatypes	Modifies lexical syntax.
7	Feature-based program configuration language	Defines a configuration language distinct from Scheme.
10	#, external form	Modifies lexical syntax.
22	Running Scheme Scripts on Unix	Does not specify a library.
30	Nested Multi-line Comments	Modifies lexical syntax (subsumed by R6RS).
34	Exception Handling for Programs	Subsumed by R6RS.
36	I/O Conditions	Subsumed by R6RS.
37	args-fold: a program argument processor	Does not specify a library.
40	A Library of Streams	Deprecated by SRFI 41, Streams.
49	Indentation-sensitive syntax	Modifies lexical syntax.
55	require-extension	Modifies semantics of top-level programs.
58	Array Notation	Modifies lexical syntax.
62	S-expression comments	Modifies lexical syntax (subsumed by R6RS).
70	Numbers	Modifies standard semantics for number system.
72	Hygienic macros	Modifies macro expansion semantics.
88	Keyword objects	Modifies lexical syntax.
89	Optional positional and named parameters	Modifies syntax and semantics of application, which cannot be provided by a library. Dependent on lexical syntax modification (SRFI 88).
90	Extensible hash table constructor	Dependent on lexical syntax modification (SRFI 88).
94	Type-Restricted Numerical Functions	Dependent on number system modification (SRFI 70).

Withdrawn SRFIs

Future SRFIs

Authors of future SRFIs that specify libraries may choose names as they please, but they are encouraged to use library names following the naming convention of this SRFI. If names are chosen that are not compatible with the referencing scheme given here, authors should specify alternative names that can be used to refer to the library consistent with this specification.

SRFI 41, Streams, for example, specifies that its libraries are named by (streams), (streams primitive), and (streams derived), but according to this SRFI, they must also be named with the prefix (srfi :41 *).

Issues with existing SRFIs and R⁶RS

There are many issues involved in the use and implementation of some of the existing SRFIs in an R⁶RS or related system. This SRFI resolves none of them.

See the discussion archive and previous revisions of this document for a list of some of these issues.

Relation to SRFIs 0 and 7

Both SRFI 0, Feature-based conditional expansion construct, and SRFI 7, Feature-based program configuration language, use feature identifiers of the form srfi-N, with the expectation "that features will eventually be assigned meaningful names (aliases) by the SRFI editors to make reading and writing code less tedious than when using srfi-N feature identifiers."

It is recommended that implementations which support SRFIs 0 or 7 use the SRFI names defined here as aliases. SRFI feature identifiers are constructed by

1. interpolating library references with a hyphen (-),
2. interpreting the SRFI number component of a library reference ":n" as "n".

For example, the feature identifier for SRFI 1, List Library, is srfi-1, or equivalently, srfi-1-lists. Feature identifiers for sub-libraries are constructed in the same way, so for example the feature identifier for the streams primitive library is srfi-41-streams-primitive.

Implementation

Acknowledgments

For discussions, I thank Will Clinger, Aziz Ghuloum, Dave Herman, Olin Shivers, Andre van Tonder, and my fellow SRFI editors. I also thank all those who participated during the draft period of this SRFI.

References

Revised⁶ Report on the Algorithmic Language Scheme

Michael Sperber, et al. (Editors)
http://www.r6rs.org/

A proposal for an Extended R⁵RS Scheme

William Clinger, et al.
http://scheme-punks.cyber-rush.org/wiki/index.php?title=ERR5RS:Charter

Ikarus Scheme

http://www.cs.indiana.edu/~aghuloum/ikarus/

Larceny

http://www.ccs.neu.edu/home/will/Larceny/

PLT Scheme

http://plt-scheme.org/

Scheme 48

http://s48.org/

Copyright

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

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

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. REMEMBER, THERE IS NO SCHEME UNDERGROUND. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.