[[R6rsChapter]]

R6RS standard libraries
-----------------------

This chapter explains which features of the R6RS standard
libraries are available in each of Larceny's major modes
of execution.

Larceny was the first substantially complete implementation
of the R6RS.  Any features that are missing from R6RS modes
are missing because of bugs or because the features are
deprecated in Larceny.
The most up-to-date listing of Larceny's known deviations
from the R6RS standard can be found on the web page
that describes the current status of
http://larceny.ccs.neu.edu/larceny-trac/wiki/DargoMode[Larceny's R6RS-compatible mode].

Larceny is R6RS-compatible but not R6RS-conforming.
When Larceny is said to support a feature of the R6RS,
that means the feature is present and will behave as
specified by the R6RS so long as no exception is raised.
Larceny does not always raise the specific conditions
specified by the R6RS, and does not perform all of the
checking for portability problems that is mandated by
the R6RS.  These deviations do not affect the execution
of production code, and do not compromise Larceny's
traditional safety.


[[R6rsBaseSection]]

Base library
~~~~~~~~~~~~

ERR5RS and R6RS modes support all procedures and syntaxes
exported by the `(rnrs base)` library.

Larceny's R5RS mode does not support `library`, `import`, or
`identifier-syntax`.

The following deviations from R6RS semantics are known bugs
that should be fixed in a future release.

In Larceny v0.96, the imaginary part of an inexact real is
inexact.  Some of the algebraic and transcendental functions
do not yet behave as specified by the R6RS, especially with
regard to branch cuts.

The `number->string` and `string->number` procedures do not
yet support mantissa widths.

The semantics of `quasiquote`, `let-syntax`, and `letrec-syntax`
differ between the R5RS and the R6RS.  Larceny's R5RS mode still
supports the R5RS semantics.


[[R6rsUnicodeSection]]

Unicode
~~~~~~~

All of Larceny's modes support all features of the `(rnrs unicode)`
library.

Larceny v0.96 conforms to
<<Standards, The Unicode Standard>>, Version 5.0.


[[BytevectorsLibrary]]
[[R6rsBytevectorsSection]]

Bytevectors
~~~~~~~~~~~

ERR5RS and R6RS modes support all procedures and syntaxes
exported by `(rnrs bytevectors)`, but the `endianness`
syntax is deprecated because it is redundant with `quote`.
Larceny's R5RS mode does not support `endianness`.

In Larceny, any symbol names a supported endianness.
The symbols `big` and `little` have their expected meanings.
All other symbols mean `(native-endianness)` with respect
to integer operations, but mean the opposite of
`(native-endianness)` with respect to
<<Standards, IEEE-754>> operations.
For string operations, the endianness must be the symbol
`big` or the symbol `little`.  All of these extensions are
permitted by the R6RS standard.

Larceny's `utf16->string` and `utf32->string` accept one,
two, or three arguments.  The R6RS specification of these
procedures does not allow them to accept a single argument,
but that is believed to be an error in the R6RS.


[[R6rsListsSection]]

Lists
~~~~~

All of Larceny's modes support all features of the
`(rnrs lists)` library.


[[R6rsSortingSection]]

Sorting
~~~~~~~

All of Larceny's modes support all features of the
`(rnrs sorting)` library.


[[R6rsControlSection]]

Control
~~~~~~~

All of Larceny's modes support all features of the
`(rnrs control)` library.


[[R6rsRecordsSection]]

Records
~~~~~~~

ERR5RS and R6RS modes support all procedures and syntaxes
exported by
`(rnrs records procedural)`,
`(rnrs records inspection)`, and
`(rnrs records syntactic)`.

Those libraries are deprecated, however;
the `make-record-constructor-descriptor` procedure does
not simplify unusually complex cases enough to justify
the complexity it adds to typical cases, and
the entire syntactic layer is gratuitously incompatible
with the procedural layer.

Larceny's R5RS mode supports all features of the deprecated
`(rnrs records procedural)` and `(rnrs records inspection)`
libraries.  R5RS mode does not support `(rnrs records syntactic)`.

All of Larceny's modes support all features of the
<<Err5rsRecordsProceduralSection, `(err5rs records procedural)`>>
and
<<Err5rsRecordsInspectionSection, `(err5rs records inspection)`>>
libraries.  ERR5RS and R6RS modes also support the
<<Err5rsRecordsSyntacticSection, `(err5rs records syntactic)`>>
library.

The record definition syntax of
http://srfi.schemers.org/srfi-9/[SRFI 9]
is a proper subset
of the syntax provided by the `(err5rs records syntactic)`
library.  In R5RS mode, SRFI 9 can be loaded dynamically
using the
<<require, `require`>> procedure:

----------------------------------------------------------------
    > (require 'srfi-9)
----------------------------------------------------------------

We recommend the ERR5RS and/or SRFI 9 libraries be used instead
of the corresponding R6RS libraries.

[WARNING]
================================================================
The R6RS spouts some tendentious nonsense about procedural
records being slower than syntactic records, but this is not
true of Larceny's records, and is unlikely to be true of other
implementations either.
================================================================

[WARNING]
================================================================
Larceny continues to support its old-style
records, which are almost but not quite compatible
with ERR5RS and R6RS records.  This can be confusing,
since some of Larceny's procedures have the same names
as R6RS procedures.  That has made it necessary to overload
those procedures to work with both old-style and R6RS
records.  We apologize for the mess.
================================================================


[[R6rsExceptionsSection]]
[[R6rsConditionsSection]]

Exceptions and conditions
~~~~~~~~~~~~~~~~~~~~~~~~~

All of Larceny's modes support all features of the
`(rnrs exceptions)` and `(rnrs conditions)` libraries.


[[R6rsIoSection]]

Input and output
~~~~~~~~~~~~~~~~

ERR5RS and R6RS modes support all names exported by the
`(rnrs io ports)`, `(rnrs io simple)`, and
`(rnrs files)` libraries.

The `buffer-mode`, `eol-style`, and `error-handling-mode`
syntaxes are deprecated because they are redundant
with `quote`.  These deprecated syntaxes may be provided
in the form of procedures rather than syntax, but this
deviation from R6RS semantics cannot be detected by
portable R6RS programs.

Larceny's R5RS mode supports all non-deprecated features
of those libraries.

Larceny supports four distinct buffer modes: `none`,
`line`, `datum`, and `block`.  The R6RS requires
the `buffer-mode` syntax to raise an exception for the
`datum` buffer mode, which is the buffer mode Larceny
uses for interactive output ports.

In Larceny, any symbol names a supported end-of-line
style.  All end-of-line and error-handling-mode symbols
whose meanings are not described by the R6RS have
locale-dependent meanings, which is an extension
permitted by the R6RS standard.

Although Larceny supports the UTF-16 codec, it is not
really useful on Windows machines (where it should be
most useful) because Larceny's low-level file system
mimics a byte-oriented Unix file system even on
Windows.  This problem should be addressed in some
future version of Larceny.

The most up-to-date list of known deviations from R6RS
io semantics can be found on the web page
that describes the current status of
http://larceny.ccs.neu.edu/larceny-trac/wiki/DargoMode[Larceny's R6RS-compatible mode].


[[R6rsProgramsSection]]

Programs
~~~~~~~~

ERR5RS and R6RS modes support the `(rnrs programs)` library.

Larceny's R5RS mode provides the `exit` procedure but
not the `command-line` procedure of that library.
Larceny's traditional `command-line-arguments` procedure
can be used to implement an approximation to `command-line`.
For a definition, see `lib/R6RS/rnrs/programs.sls`.


[[R6rsArithmeticSection]]

Arithmetic
~~~~~~~~~~

All of Larceny's modes support all features of the
`(rnrs arithmetic fixnums)`,
`(rnrs arithmetic flonums)`, and
`(rnrs arithmetic bitwise)`
libraries.

[NOTE]
================================================================
R6RS fixnum and flonum operations may be slower than the
corresponding generic operations, since the fixnum and flonum
operations are required to check their arguments and may also
have to check their results.
Isolated operations in small micro-benchmarks are likely to
be slower than groups of similar operations in larger programs,
because the Twobit compiler removes redundant checks and
propagates type information.
================================================================


[[R6rsSyntaxCaseSection]]

Syntax-case
~~~~~~~~~~~

ERR5RS and R6RS modes support the `(rnrs syntax-case)` library.
Larceny's R5RS mode does not.


[[R6rsHashtablesSection]]

Hashtables
~~~~~~~~~~

All of Larceny's modes support all features of the
`(rnrs hashtables)` library.

[NOTE]
================================================================
Larceny's traditional `make-hashtable` procedure has been
renamed to `make-oldstyle-hashtable`.  In Larceny v0.96,
`make-hashtable` prints a warning when it is called.  To
avoid that warning, call `make-r6rs-hashtable` instead.
================================================================


[[R6rsEnumerationsSection]]

Enumeration sets
~~~~~~~~~~~~~~~~

ERR5RS and R6RS modes support the `(rnrs enums)` library.
Larceny's R5RS mode provides all of the procedures exported by
`(rnrs enums)` but does not provide the `define-enumeration`
syntax.


[[R6rsEvalSection]]

Eval
~~~~

ERR5RS and R6RS modes are believed to support the `(rnrs eval)`
library, but the `environment` procedure has not been tested.
Larceny's R5RS mode provides an R5RS-compatible eval procedure,
not an R6RS-compatible eval procedure, and does not provide the
`environment` procedure.


[[R6rsMutablePairsSection]]
[[R6rsMutableStringsSection]]

Mutable pairs and strings
~~~~~~~~~~~~~~~~~~~~~~~~~

All of Larceny's modes support all features of the
`(rnrs mutable-pairs)` and `(rnrs mutable-strings)` libraries.


[[R6rsR5rsSection]]

R5RS
~~~~

All of Larceny's modes support all features of the
`(rnrs r5rs)` library.


