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## 9. 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.

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 or expected. 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.

For example, Larceny has extended the R6RS `library` syntax to allow R6RS libraries to import R7RS libraries even when the names of those imported libraries use the more liberal R7RS syntax.

Furthermore, Larceny has extended several R6RS procedures so they behave as specified by the newer R7RS (small) standard. In Larceny, for example, the `utf8->string` procedure accepts one, two, or three arguments, and the `finite?` procedure accepts any object as its argument. According to the R6RS, `utf8->string` must raise an exception when passed more than one argument, and `finite?` must raise an exception if it detects an argument that is not a real number. Although the R6RS says these exceptions are "absolute requirements", they interfere with interoperability between R6RS and R7RS code, and are best honored in the breach.

### 9.1. Base library

R7RS 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`.

### Note

As of v0.99, Larceny ignores the R6RS `for` and `meta` keywords of R6RS `library` syntax, which were intended to enforce proper phasing in libraries and programs that define `syntax-case` macros. Several other implementations of the R6RS have been ignoring those keywords, and there is growing consensus that they are unnecessary and unhelpful.

### Note

The semantics of `quasiquote`, `let-syntax`, and `letrec-syntax` differ between the R5RS, R6RS, and R7RS. Larceny's R5RS mode still supports the R5RS semantics. R7RS and R6RS modes support the R6RS semantics.

### 9.2. Unicode

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

Larceny v0.99 conforms to The Unicode Standard, Version 7.0.

### 9.3. Bytevectors

R7RS 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 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.

### 9.4. Lists

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

### 9.5. Sorting

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

### 9.6. Control

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

### 9.7. Records

R7RS 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 extends the R7RS `define-record-type` syntax exported by `(scheme base)` to accept the deprecated R6RS syntax, and extends the deprecated `define-record-type` syntax exported by `(rnrs records syntactic)` to accept R7RS syntax. Larceny's unification of the two syntaxes within a single implementation of `define-record-type` allows libraries and programs to import both `(scheme base)` and `(rnrs)` without having to rename one version of `define-record-type`.

Larceny also extends its unified R7RS/R6RS `define-record-type` to support all features of `(srfi :99 records syntactic)` and `(srfi 131)`. So long as the deprecated R6RS syntax is not used, Larceny's `define-record-type` is fully compatible with the procedural layers defined by `(srfi :99 records procedural)` and by `(rnrs records procedural)`.

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 `(err5rs records procedural)` and `(err5rs records inspection)` libraries. R7RS and R6RS modes also support the `(err5rs records syntactic)` library. These libraries are equivalent to the `(srfi :99 records procedural)`, `(srfi :99 records inspection)`, and `(srfi :99 records syntactic)` libraries.

The record definition syntax of 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` procedure:

        > (require 'srfi-9)

We recommend the R7RS, SRFI 9, and/or SRFI 131 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 R7RS 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.

### 9.8. Exceptions and conditions

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

### 9.9. Input and output

R7RS 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`. Larceny may provide these deprecated syntaxes 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 Larceny's R6RS-compatible mode.

### 9.10. Programs

R7RS 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`.

### 9.11. 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, however, because Larceny's compiler removes redundant checks and propagates type information.

### 9.12. Syntax-case

R7RS and R6RS modes support the `(rnrs syntax-case)` library. Larceny's R5RS mode does not.

### 9.13. 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`.

### Note

When you use Larceny's R5RS or R7RS mode to dump a heap image that contains `eq?` or `eqv?` hashtables you have created, they are automatically reset so they will rehash themselves whenever you begin a new session with the dumped heap.

### 9.14. Enumeration sets

R7RS 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.

### 9.15. Eval

R7RS and R6RS modes support the `(rnrs eval)` library. Larceny's R5RS mode provides an R5RS-compatible eval procedure, not an R6RS-compatible eval procedure, and does not provide the `environment` procedure.

### 9.16. Mutable pairs and strings

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

### 9.17. R5RS

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

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