ABOUT R7RS

The Scheme programming language is described by the R7RS (small)
standard, which was approved in 2013 by 86% of the voters [1].

The R7RS standard extends and is mostly compatible with the
older R5RS and IEEE standards [2].  The most significant
incompatibility is case-sensitivity: By default, R7RS lexical
syntax is case-sensitive whereas R5RS and IEEE 1178 syntax is
not.

The R7RS is not entirely compatible with the previous R6RS
standard [3], mainly because R7RS lexical syntax differs from
R6RS lexical syntax in several respects.

The R7RS allows implementations to extend its lexical syntax.
To preserve backward compatibility, Larceny accepts both R7RS
and R6RS lexical syntax.  Larceny also accepts R6RS library
syntax as an alternative to R7RS define-library syntax.  In
Larceny, the language described by the older R6RS standard is
a proper subset of the R7RS language as extended by Larceny.


R7RS READ/EVAL/PRINT LOOP

To interact with a traditional read/eval/print loop, invoke
Larceny with the -r7rs or -r7r6 option:

    larceny -r7rs
or
    larceny -r7r6

The -r7rs option imports the R7RS (scheme base) library, while
the -r7r6 option imports all of the standard R7RS and R6RS
libraries (renaming the R6RS bytevector-copy! procedure to
r6rs:bytevector-copy! because it would otherwise conflict with
the R7RS bytevector-copy! procedure).

You can define or import additional libraries while interacting
with the read/eval/print loop.


RUNNING AN R7RS PROGRAM

To execute an R7RS program that is contained within a file named
pgm, type:

    larceny -r7rs -program pgm
or
    larceny -r7r6 -program pgm


RUNNING AN R7RS PROGRAM WITH ADDITIONAL LIBRARIES

To execute an R7RS program that is contained within a file named
pgm and uses libraries defined within other files in the current
directory, type:

    larceny -r7rs -path . -program pgm
or
    larceny -r7r6 -path . -program pgm

Files that contain library definitions must be named using
Larceny's standard naming conventions, which are specified in
Larceny's user manual [4].  Libraries and programs can use the
R7RS cond-expand facility to determine whether specific
libraries are available.


R7RS PROGRAMS

An R7RS program is a sequence of declarations, definitions,
and expressions.  R7RS programs subsume R6RS and R5RS programs.
An R6RS top-level program is equivalent to an R7RS program
that begins with an import declaration and contains no other
declarations.  An R5RS program is equivalent to an R7RS program
that contains no declarations at all.


DEFINING LIBRARIES

As an extension to the R7RS, Larceny allows programs to define
R7RS libraries within the file that contains the program.  These
library definitions must come before the program itself and be
arranged so that no library depends upon libraries that come
later in the file.

This extension is supported by the Chicken implementation of
R7 Scheme and may be supported by other implementations as well,
but it is not fully portable.  Some implementations of the R7RS
may require every library definition to be placed within a
separate file.


LIBRARY PATH

As an extension to the R7RS, Larceny automatically loads
libraries when they are first imported, provided Larceny can
find the libraries in its library search path.  The library
search path defaults to a path that contains the predefined
libraries listed in Larceny's user manual [4], but more
directories can be added to the library search path using
Larceny's -path command-line option.

Autoloaded libraries must be defined in files that follow
Larceny's standard naming conventions for R7RS/R6RS library
files.  These naming conventions are described in Larceny's
user manual [4].

Several other implementations of R7 Scheme provide a similar
feature, but some apparently do not.  Some implementations may
provide a similar feature but use a mapping from library names
to file names that differs from Larceny's mapping.


LIBRARY PATH ENVIRONMENT VARIABLE

As an extension to the R7RS, Larceny allows the library path to
be specified by a LARCENY_LIBPATH environment variable instead
of the --path command-line option.


PREDEFINED LIBRARIES

In addition to the standard R7RS libraries, Larceny predefines a
variety of other libraries that R7RS programs and libraries can
import.  For a partial list of these predefined libraries, see
Larceny's user manual [4].

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[1] http://www.scheme-reports.org/
[2] http://www.schemers.org/Documents/Standards/
[3] http://www.r6rs.org/
[4] http://larceny.ccs.neu.edu/doc/
