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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.
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:
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.
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:
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
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> ...),
<identifier> is one of the included
SRFI library names defined below, and
10> is a SRFI number. The non-terminals
<uinteger 10> and
are defined as given in R6RS Chapter
4, Lexical syntax.
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.
A SRFI Library can be referenced by number, as in
or equivalently using the library's name, as in
(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
derived libraries within the
streams library. These can be referenced as
(srfi :41 streams primitive),
(srfi :41 streams derived).
Mnemonic library names are chosen according to the following
conventions: Libraries that define datatypes are typically pluralized
Libraries that provide new expression forms are named by the name of
their new form (e.g.,
and-let*). Libraries that define a single procedure (or
that have a primary procedure) are given the name of the procedure
cat). Libraries that provide
a large API of syntaxes and values are named in a descriptive manner
derived from their title (e.g.,
real-time-multithreading). This naming convention is
consistent with the names chosen in the R6RS Standard
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
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.
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
clear that making the alternative binding for
available as a library binding is desirable. Authors that wish to
use SRFI 5's
let, rather than R6RS's
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
because the SRFI 63 document does not explicitly state this should
replace the standard
The following SRFI library names are defined:
|2||and-let*||AND-LET*: an AND with local bindings, a guarded LET* special form|
|5||let||A compatible let form with signatures and rest arguments|
|6||basic-string-ports||Basic String Ports|
|9||records||Defining Record Types|
|11||let-values||Syntax for receiving multiple values|
|16||case-lambda||Syntax for procedures of variable arity|
|19||time||Time Data Types and Procedures|
|21||real-time-multithreading||Real-time multithreading support|
|23||error||Error reporting mechanism|
|25||multi-dimensional-arrays||Multi-dimensional Array Primitives|
|26||cut||Notation for Specializing Parameters without Currying|
|27||random-bits||Sources of Random Bits|
|28||basic-format-strings||Basic Format Strings|
|31||rec||A special form for recursive evaluation|
|38||with-shared-structure||External Representation for Data With Shared Structure|
|41||streams, streams primitive, streams derived||Streams|
|45||lazy||Primitives for expressing iterative lazy algorithms|
|46||syntax-rules||Basic Syntax-rules Extensions|
|48||intermediate-format-strings||Intermediate Format Strings|
|51||rest-values||Handling rest list|
|60||integer-bits||Integers as Bits|
|61||cond||A more general |
|63||arrays||Homogeneous and Heterogeneous Arrays|
|64||testing||A Scheme API for test suites|
|69||basic-hash-tables||Basic hash tables|
|74||blobs||Octet-Addressed Binary Blocks|
|86||mu-and-nu||MU and NU simulating VALUES & CALL-WITH-VALUES, and their related LET-syntax|
|87||case||=> in case clauses|
|95||sorting-and-merging||Sorting and Merging|
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||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||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).|
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
(streams primitive), and
(streams derived), but according to this SRFI, they must
also be named with the prefix
(srfi :41 *).
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.
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
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
:n" as "
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
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.
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