.\" S9(1) Manual Page
.\" By Nils M Holm, 2007-2015
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.SH NAME
.B "s9
- Scheme Interpreter
.SH USAGE
.B "s9 [\-hv?] [\-i name|\-] [\-gqu] [\-d image] [\-e expr]
.B "   [\-k size[m]] [\-l prog] [\-n size[m]] [\-r expr]
.B "   [\-f prog [args]] [\-\- [args]] [prog [args]]"
.SH "DESCRIPTION
.B "Scheme 9 from Empty Space
is an interpreter for R4RS Scheme with some additional procedures
for accessing typical Unix system calls and Unix and Curses library
functions (if compiled-in). The
.B s9
command starts the interpreter.
.SH "OPTIONS
.B "\-h, \-v, or \-?
.in +4
Display a brief summary of options.
.in -4
.B "\-i name | \-
.in +4
Load alternative image file `\fIname\fP.image'. When no image file
can be found, try to load `\fIname\fP.scm'. The file will be searched
in the entire
.I S9FES_LIBRARY_PATH
(see below). When this option is used, it
.B must
be the first one of the s9 command.
.br
When `\-' is specified as \fIname\fP, no heap image will be loaded,
and the core library will be read from the source file `s9.scm'.
.in -4
.B "\-d file
.in +4
Dump heap image to
.I file
and exit.
.in -4
.B "\-e expr
.in +4
Read expression from argument, evaluate, and print value. Multiple
.B \-e
options may be given, which will evaluate from left to right.
Interactive mode will not be entered.
.in -4
.B "\-f program [argument ...]
.in +4
Run
.I program
and exit (implies \-q). When there are any
.IR argument s,
they are passed to the
.IR program ,
where they can be extracted from the
.B *arguments*
variable. This option must be the last one. The
.B -f
flag is optional.
.in -4
.B "-g[g]
.in +4
Print GC summaries. A single `g' will report pool growth, a second
`g' will also include data about pool usage after each collection.
.in -4
.B "\-k N[m]
.in +4
Set vector limit to
.I N
kilo (or mega) nodes (\fB-k 0\fP
means no limit; use with care!).
.in -4
.B "\-l program
.in +4
Load
.I program
before entering the REPL or processing
.BR \-f
(may be repeated).
.in -4
.B "\-n N[m]
.in +4
Set node limit to
.I N
kilo (or mega) nodes (\fB\-n 0\fP
means no limit; use with care!).
.in -4
.B "\-q
.in +4
Be quiet: skip banners and prompts, exit on errors.
.in -4
.B "\-r expr
.in +4
Like
.BR \-e ,
but no value will print. Used to run expressions for effect.
.in -4
.B "\-u
.in +4
Short for \fB-k 0 -n 0\fP (use unlimited memory).
.in -4
.B "\-\- [argument ...]
.in +4
Arguments following
.B \-\-
are not interpreted by S9fES, but bound to the
.B *arguments*
variable instead. This option must be the last one.
.in -4
.SH "ONLINE HELP
When the interpreter is running and the default heap image is loaded,
just type \fB(help)\fP or \fB,h\fP to invoke the online help system.
When the online help system is not loaded, you will have to run the
following command first:
.sp
\fB(load\-from\-library "help.scm")\fP
.SH "META COMMANDS
In order to facilitate the invocation of frequently-used top-level
procedures,
.B s9
provides the following "meta commands" (they work only when entered
directly at the
.B s9
prompt):
.sp
.in +4
.nf
\fB,a text\fP  =  (apropos "text")
\fB,h text\fP  =  (help "text")
\fB,l file\fP  =  (load\-from\-library "file")
\fB,q     \fP  =  (sys:exit)
.fi
.in -4
.sp
The arguments of \fB,a\fP and \fB,h\fP are optional.
.SH "ADDITIONS
S9fES supports nestable block comments of the form
.sp
.in +4
.nf
\fB#|\fP \fIcomment ...\fP \fB|#\fP.
.fi
.in -4
.sp
Square brackets may be used in the places of parentheses:
.sp
.in +4
.nf
\fB(cond [(foo) (bar)])\fP.
.fi
.in -4
.sp
The same type of bracket must be used on both ends of a list.
.sp
These S9fES procedures are not in R4RS:
.sp
.ne 3
.B "(argv integer)  ==>  string | #f
.in +4
Retrieve the value of the given command line argument. Return
\fB#f\fP, if there are less than \fIinteger\fP+1 arguments.
Arguments start at 0.
.in -4
.sp
.ne 3
.B "(bit\-op integer1 integer2 integer3 ...)  ==>  integer | #f
.in +4
Implement a variety of bitwise operations. See the
.B bit\-op
help page for details.
.in -4
.sp
.ne 3
.B "(delete\-file string)  ==>  unspecific
.in +4
Delete the file specified in the
.I string
argument. If the file does not exist
or cannot be deleted, report an error.
.in -4
.sp
.ne 3
.B "(environ string)  ==>  string | #f
.in +4
Retrieve the value of the given environment variable. Return
\fB#f\fP, if the variable is undefined.
.in -4
.sp
.ne 3
.B "(error string)         ==>  undefined
.br
.B "(error string object)  ==>  undefined
.in +4
Print an error message of the form
.I "error: string: object
and terminate program execution.
.in -4
.sp
.ne 3
.B "(eval object1)          ==>  object
.br
.B "(eval object1 object2)  ==>  object
.in +4
Evaluate
.I object1
in the current environment and return its normal form.
If
.I object2
is also specified, it is ignored.
.in -4
.sp
.ne 3
.B "(exponent real)  ==>  integer
.in +4
Extract the exponent part from a real number.
.in -4
.sp
.ne 3
.B "(file\-exists? string)  ==>  boolean
.in +4
Return
.B "#t
if the file specified in the
.I string
argument exists and otherwise \fB#f\fP.
.in -4
.sp
.ne 4
.B "(fold\-left proc base list ...)  ==>  object
.in +4
Combine the elements of the
.IR list s
using
.IR proc .
Combine elements left-associatively.
.I Base
is the leftmost element.
.in -4
.sp
.ne 4
.B "(fold\-right proc base list ...)  ==>  object
.in +4
Combine the elements of the
.IR list s
using
.IR proc .
Combine elements right-associatively.
.I Base
is the rightmost element.
.in -4
.sp
.B "(gensym)         ==>  symbol
.br
.B "(gensym symbol)  ==>  symbol
.br
.B "(gensym string)  ==>  symbol
.in +4
Return a fresh symbol. When a
.I string
or
.I symbol
argument is given, use it as prefix for the fresh symbol.
.in -4
.sp
.ne 2
.B "(load\-from\-library string)  ==>  unspecific
.in +4
Attempt to
.B load
the file
.I string
from each directory of
.IR S9FES_LIBRARY_PATH .
.in -4
.sp
.ne 2
.B "(locate\-file string)  ==>  string | #f
.in +4
Search for the file
.I string
in each  directory of
.I S9FES_LIBRARY_PATH
in sequence.
When the file can be located, return its full path, else
return \fB#f\fP.
.in -4
.sp
.ne 3
.B "(macro\-expand object)  ==>  object
.br 
.B "(macro\-expand\-1 object)  ==>  object
.in +4
If
.I object
is a list resembling a macro application, return the expanded form,
else return the object.
.B Macro\-expand\-1
expands macros only once while
.B macro\-expand
expands them recursively.
.in -4
.sp
.ne 3
.B "(mantissa real)  ==>  integer
.in +4
Extract the mantissa part from a real number.
.in -4
.sp
.ne 2
.B "(print object ...)  ==>  unspecific
.in +4
Write multiple
.IR object s
separated by spaces.
.in -4
.sp
.ne 2
.B "(require\-extension ext ...)  ==>  unspecific
.in +4
Require the named extensions to be compiled-in. Signal an error
if not all of the required extensions are present.
.I Ext
may be of the form \fI(or ext1 ext2 ...)\fP. In this case,
it is sufficient if at least one of the given \fIext\fPs is present.
.in -4
.sp
.ne 2
.B "(reverse! list)  ==>  list
.in +4
Reverse
.I list
destructively and return the reverse list.
.in -4
.sp
.ne 2
.B "(set\-input\-port! input\-port)  ==>  unspecific
.in +4
Destructively set the current input port.
.in -4
.sp
.ne 2
.B "(set\-output\-port! output\-port)  ==>  unspecific
.in +4
Destructively set the current output port.
.in -4
.sp
.ne 2
.B "(stats form)  ==>  form
.in +4
Evaluate the given
.I form
and return a list containing its normal form plus a summary
of the resources used to compute that normal form:
.sp
.in +4
.nf
- reduction steps
- conses allocated
- total nodes allocated
- garbage collections
.fi
.in -4
.sp
Each resource count will be returned as a group of integers
representing ones, thousands, millions, etc. Note that
.I form
must be quoted or it will be evaluated before passing it to
.BR stats .
.in -4
.sp
.ne 2
.B "(symbols)  ==>  list
.in +4
Return a list of all defined symbols.
.in -4
.sp
.ne 3
.B "(system string)  ==>  number
.in +4
Run the given shell command and return its exit code.
.in -4
.sp
.ne 3
.B "(vector\-append vector ...)  ==>  vector
.in +4
Return a fresh vector containing the concatenation of the given
vectors.
.in -4
.sp
.ne 3
.B "(vector\-copy vector)                           ==>  vector
.br
.B "(vector\-copy vector integer)                   ==>  vector
.br
.B "(vector\-copy vector integer1 integer2)         ==>  vector
.br
.B "(vector\-copy vector integer1 integer2 object)  ==>  vector
.in +4
Return a copy of the given vector. When
.I integer1
is specified, skip the given number of elements. When
.I integer2
is also specified, copy elements from
.I integer1
up to, but not including,
.IR integer2 .
When
.I integer2
exceeds the size of the original vector, add unspecific slots to the
copy. When an
.I object
argument is given, fill extra slots with that argument.
.in -4
.sp
.ne 3
.B "(void)  ==>  unspecific
.in +4
Return an unspecific value.
.in -4
.sp
Refer to the help pages for descriptions of the Scheme 9 extension
procedures.
.SH "SPECIAL VARIABLES
These variables are predefined in the dynamic top-level scope of the
interpreter.
.sp
.ne 2
.B "** (form)
.in +4
The normal form of the expression most recently evaluated at the
top level.
.in -4
.ne 2
.B "*arguments* (list of strings)
.in +4
A list of command line arguments passed to the
.I "Scheme program
(not to the interpreter), i.e. the
.I args
in \fIs9 -f file args\fP.
.in -4
.ne 2
.B "*extensions* (list of symbols)
.in +4
Compiled-in extensions.
.in -4
.ne 2
.B "*host-system* (symbol)
.in +4
The host system running the \fBs9\fP interpreter: \fBunix\fP, \fBplan9\fP, or
.B "#F
(unknown).
.in -4
.ne 2
.B "*library-path* (string)
.in +4
A verbatim copy of the
.I S9FES_LIBRARY_PATH
environment variable (see below).
.in -4
.ne 2
.B "*loading* (boolean)
.in +4
Set to
.B #t
when \fBload\fPing a file, else \fB#f\fP.
.in -4
.SH "MACROS
A macro is a procedure that is applied to its unevaluated arguments.
The macro application is replaced with the value returned by the procedure.
This happens before the expression containing the macro application is
evaluated, so a macro
.I rewrites
its own application:
.sp
.ne 2
.nf
(define\-syntax (when p . c)
  `(if ,p (begin ,@c)))
(macro\-expand '(when (= 1 1) (display "true") (newline) #t))
  ==>  (if (= 1 1)
           (begin (display "true")
                  (newline)
                  #t))
(when (= 1 1) 1 2 3)  ==>  3
.fi
.sp
The
.B define\-syntax
form introduces a new macro:
.sp
.ne 3
.B "(define\-syntax name procedure)        ==>  unspecific
.br
.B "(define\-syntax (name args ...) body)  ==>  unspecific
.sp
Both of these forms introduce the keyword
.I name
and bind it to a procedure. The first form requires the
second argument to be a procedure. Like in
.B define
forms the second variant implies a procedure definition.
.sp
Macros may contain applications of macros that were defined earlier.
Macros may not recurse directly, but they may implement recursion
internally using
.B letrec
or by rewriting their own applications. The following macro,
for example, does
.I not
work, because
.I d
is undefined in the body of
.IR d :
.sp
.B "(define\-syntax (d x) (and (pair? x) (d (cdr x)))) ; wrong"
.sp
The following version
.I does
work, though:
.sp
.B "(define\-syntax (d x) (and (pair? x) `(d ,(cdr x)))) ; OK"
.sp
The body of
.B define\-syntax
may be a
.B syntax\-rules
transformer, as described in R4RS, if the
.B syntax\-rules
extension has been loaded.
.SH "TECHNICAL DETAILS
S9fES is a tree-walking interpreter using deep binding and hashed
environments. It employs an extremely reliable[1] constant-space mark
and sweep garbage collector with in-situ string and vector pool
compaction. Memory pools grow on demand. The interpreter uses
arbitrary-precision integer arithmetics and decimal-based real number
arithmetics.
.SH "INTERPRETER START-UP
When the
.B s9
interpreter is started, the following steps will be performed in this
order:
.sp
Load library.
.in +4
The interpreter searches its library path (either built-in or specified
in the
.I S9FES_LIBRARY_PATH
environment variable)
for a heap image file or the library source code. The heap image file
is the name of the interpreter with a
.I .image
suffix appended. An alternative name can be specified with the
.B \-i
option (see
.BR OPTIONS ).
The default library source code is named
.IR s9.scm .
First all directories of the library path are searched for images,
then the directories are searched for library sources.
.in -4
.sp
Initialize extensions.
.in +4
Any extensions compiled into the interpreter are initialized by calling
the nullary procedure
.B ext:ext
(where
.B ext
is the name of the extension). The procedures are optional. The last
`extension' being initialized is
.B S9
itself, so when a procedure named
.B s9:s9
exists, it will be called at this point.
.in -4
.sp
Evaluate command line options.
.in +4
When a
.B "\-l file
option is found, the program contained in the given file will be
.BR load ed.
When a
.B "\-f file args
option is found, the program contained in the file will be run and then
S9 will exit.
.B Args
will be passed to the program.
.in -4
.sp
.ne 2
Enter REPL.
.in +4
Interactive mode is only entered, when no
.BR \-e ,
.BR \-f ,
or
.BR \-r
option was given and no program was specified.
.in -4
.SH "ALLOCATION STRATEGY
The S9fES memory pools grow exponentially until the memory limit
is reached. When the limit is reached, the current computation
is aborted. A memory limit can be specified using the \fB-k\fP,
\fB-n\fP, and
.B -u
command line options. The limit is specified in units of 1024
nodes/cells (or in units of 1024*1024 nodes/cells by appending an
.B m
suffix).
.sp
Note that computations may abort
.I before
the limit is reached due to the way the pool grows. Use the
.B \-g
command line option to experiment with pool sizes.
.br
Specifying a limit of zero (or using the
.B -u
option) disables the memory limit completely
and the interpreter will allocate as much memory as it can get.
This option should be used with care.
.SH "LIMITATIONS
These parts of R4RS are not implemented:
.sp
I/O:
.B char\-ready?
(this is in the
.B sys\-unix
extension).
.br
Transcripts:
.BR transcript\-off ,
.BR transcript\-on .
.br
Rational and complex numbers and related procedures.
.br
The
.B atan
procedure does not accept a second argument.
.SH "BUGS
You may not quasiquote
.B quasiquote
unless in
.BR unquote
(e.g.:
.B ``x
does not work, but
.B `,`x
does).
.br
The macro expander will expand
.B (x)
in \fB(cond (x))\fP,
if
.B x
is a macro.
.br
.B Syntax-rules
is not fully hygienic.
.br
.B Call/cc
must be the only argument when used in
.B lambda
(or derived binding syntax, such as
.BR let ).
Not observing this rule
.I will
break the interpreter.
.SH "FILES
.ne 2
.B /usr/share/scheme9
.in +4
The S9fES procedure library (source code).
.in -4
.ne 2
.B /usr/share/scheme9/s9.image
.in +4
The interpreter heap image.
.in -4
.ne 2
.B *.scm
.in +4
Scheme source code.
.in -4
.SH "ENVIRONMENT
.B S9FES_LIBRARY_PATH
.in +4
A colon-separated list of directories which will be searched for
the s9 library when the interpreter is launched. The same directories
will be searched by the
.B locate\-file
procedure.
.br
Default:
.I \&.:~/.s9fes:/usr/share/scheme9
.in -4
.SH "SIGNALS
.ne 3
.B "SIGINT
.in +4
Abort input or terminate program execution.
.in -4
.ne 3
.B "SIGQUIT
.in +4
Terminate the interpreter process (emergency exit).
.in -4
.B "SIGTERM
.in +4
Silently terminate the interpreter process.
.in -4
.B """interrupt"""
.in +4
On Plan 9, receiving an
.I interrupt
note will abort input or terminate program execution, as
.I SIGINT
would on Unix.
.in -4
.SH "FOOTNOTES
.B [1]
See
.I comp.lang.scheme
Usenet message
.in +4
.I "<vhtzl9lupyp.fsf@maharal.csail.mit.edu>
.br
(Thu, 27 Aug 2009 13:27:42 \-0400) and its follow-ups.
.in -4
.SH "REFERENCES
.ne 3
The Revised^4 Report on the Algorithmic Language Scheme.
.in +4
.B "http://www\-swiss.ai.mit.edu/~jaffer/r4rs_toc.html
.in -4
.sp
.ne 3
Scheme 9 from Empty Space -- A Guide to Implementing Scheme in C.
.in +4
.B "Available at Lulu.com, see http://www.t3x.org
.in -4
.SH AUTHOR
Nils M Holm