made debugger handle errors in printing *DEBUG-CONDITION*

[sbcl.git] / doc / sbcl.1

.\" -*- Mode: Text -*-
.\"
.\" man page introduction to SBCL
.\"
.\" SBCL, including this man page, is derived from CMU Common Lisp, of
.\" which it was said (ca. 1991)
.\"   **********************************************************************
.\"   This code was written as part of the CMU Common Lisp project at
.\"   Carnegie Mellon University, and has been placed in the public domain.
.\"   If you want to use this code or any part of CMU Common Lisp, please
.\"   contact Scott Fahlman or slisp-group@cs.cmu.edu.
.\"   **********************************************************************
.\"
.TH SBCL 1 "$Date$"
.AT 3
.SH NAME
SBCL -- "Steel Bank Common Lisp"

.SH DESCRIPTION

SBCL is a free Common Lisp programming environment. It is derived from
the free CMU CL programming environment. (The name is intended to
acknowledge the connection: steel and banking are the industries where
Carnegie and Mellon made the big bucks.)

.SH COMMAND LINE SYNTAX

Command line syntax can be considered an advanced topic; for ordinary
interactive use, no command line arguments should be necessary.

In order to understand the command line argument syntax for SBCL, it
is helpful to understand that the SBCL system is implemented as two
components, a low-level runtime environment written in C and a
higher-level system written in Common Lisp itself. Some command line
arguments are processed during the initialization of the low-level
runtime environment, some command line arguments are processed during
the initialization of the Common Lisp system, and any remaining
command line arguments are passed on to user code.

The full, unambiguous syntax for SBCL is
.TP 3
.B sbcl [runtime options] --end-runtime-options [toplevel options] --end-toplevel-options [user options]
.PP

For convenience, the --end-runtime-options and --end-toplevel-options
elements can be omitted. Omitting these elements can be convenient
when you are running the program interactively, and you can see that
no ambiguities are possible with the option values you are using.
Omitting these elements is probably a bad idea for any batch file
where any of the options are under user control, since it makes it
impossible for SBCL to detect erroneous command line input, so that
erroneous command line arguments will be passed on to the user program
even if they was intended for the runtime system or the Lisp system.

Supported runtime options are
.TP 3
.B --core <corefilename>
Run the specified Lisp core file instead of the default. (See the FILES
section.) Note that if the Lisp core file is a user-created core file, it may
run a nonstandard toplevel which does not accept the standard toplevel options.
.TP 3
.B --noinform
Suppress the printing of any banner or other informational message at
startup. (This makes it easier to write Lisp programs which work in
Unix pipelines. See also the "--noinform" option.)
.PP

In the future, runtime options may be added to control behavior such
as lazy allocation of memory.

Runtime options, including any --end-runtime-options option,
are stripped out of the command line before the
Lisp toplevel logic gets a chance to see it.

Supported toplevel options for the standard SBCL core are
.TP 3
.B --sysinit <filename>
Load filename instead of the default system-wide
initialization file. (See the FILES section.)
There is no special option to cause
no system-wide initialization file to be read, but on a Unix
system "--sysinit /dev/null" can be used to achieve the same effect.
.TP 3
.B --userinit <filename>
Load filename instead of the default user
initialization file. (See the FILES section.)
There is no special option to cause
no user initialization file to be read, but on a Unix
system "--userinit /dev/null" can be used to achieve the same effect.
.TP 3
.B --eval <command>
After executing any initialization file, but before starting the
read-eval-print loop on standard input,
evaluate the command given. More than
one --eval option can be used, and all will be executed,
in the order they appear on the command line.
.TP 3
.B --noprint
When ordinarily the toplevel "read-eval-print loop" would be
executed, execute a "read-eval loop" instead, i.e. don't print
a prompt and don't echo results. (Combined with the --noinform
runtime option, this makes it easier to write Lisp
"scripts" which work in Unix pipelines.)
.TP 3
.B --noprogrammer
Ordinarily the system initializes *DEBUG-IO* to *TERMINAL-IO*.
When the --notty option is set, however, *DEBUG-IO* is instead
set to a stream which sends its output to *ERROR-OUTPUT* and
which raises an error on input. As a result, any attempt by the
program to get programmer feedback through the debugger
causes an error which abnormally terminates the entire
Lisp environment. (This can be useful behavior for programs
which are to run without programmer supervision.)
.PP

Regardless of the order in which --sysinit, --userinit, and --eval
options appear on the command line, the sysinit file, if it exists, is
loaded first; then the userinit file, if it exists, is loaded; then
any --eval commands are executed in sequence; then the read-eval-print
loop is started on standard input. At any step, error conditions or
commands such as SB-EXT:QUIT can cause execution to be terminated
before proceeding to subsequent steps.

Note that when running SBCL from a core file created by a user call to
the SB-EXT:SAVE-LISP-AND-DIE, the toplevel options may be under the
control of user code passed as arguments to SB-EXT:SAVE-LISP-AND-DIE.
For this purpose, the --end-toplevel-options option itself can be
considered a toplevel option, i.e. the user core, at its option, may
not support it.

In the standard SBCL startup sequence (i.e. with no user core
involved) toplevel options and any --end-toplevel-options option are
stripped out of the command line argument list before user code gets a
chance to see it.

.SH OVERVIEW

SBCL aims for but has not reached ANSI compliance.

SBCL compiles Lisp to native code, or optionally to more-compact but
much slower byte code.

SBCL's garbage collector is generational and conservative.

SBCL includes a source level debugger, as well as the ANSI TRACE
facility and a rudimentary profiler.

.SH DIFFERENCES FROM CMU CL

SBCL can be built from scratch using a plain vanilla ANSI Common Lisp
system and a C compiler, and all of its properties are specified by
the version of the source code that it was created from. (This clean
bootstrappability was the immediate motivation for forking off of the
CMU CL development tree.)

Many extensions supported by CMU CL, like Motif support,
the Hemlock editor, search paths, the WIRE protocol, various
user-level macros and functions (e.g. LETF, ITERATE, MEMQ,
REQUIRED-ARGUMENT), and many others.

SBCL has retained some extensions of its parent CMU CL. Many
of them are in three categories:
.TP 3
\--
hooks into the low level workings of the system which can be useful
for debugging (e.g. a list of functions to be run whenever GC occurs,
or an operator to cause a particular string to be compiled into a fasl
file)
.TP 3
\--
non-portable performance hacks (e.g. PURIFY, which causes
everything currently in existence to become immune to GC)
.TP 3
\--
things which might be in the new ANSI spec (e.g. weak pointers,
finalization, foreign function interface to C, and Gray streams)
.PP

There are also various retained extensions which don't fall into
any particular category, e.g.
.TP 3
\--
the ability to save running Lisp images as executable files
.PP

Some of the retained extensions have new names and/or different
options than their CMU CL counterparts. For example, the SBCL function
which saves a Lisp image to disk and kills it is called
SAVE-LISP-AND-DIE instead of SAVE-LISP, and it supports fewer keyword
options than CMU CL's SAVE-LISP.

.SH THE COMPILER

SBCL inherits from CMU CL the "Python" native code compiler. This
compiler is very clever about understanding the type system of Common
Lisp and using it to produce efficient code, and about producing notes
to let the user know when the compiler doesn't have enough type
information to produce efficient code. It also tries (almost always
successfully) to follow the unusual but very useful principle that
type declarations should be checked at runtime unless the user
explicitly tells the system that speed is more important than safety.

The CMU CL version of this compiler reportedly produces pretty good
code for modern machines which have lots of registers, but its code
for the X86 is marred by a lot of extra loads and stores to
stack-based temporary variables. Because of this, and because of the
extra levels of indirection in Common Lisp relative to C, we find a
typical performance decrease by a factor of perhaps 2 to 5 for small
programs coded in SBCL instead of GCC.

For more information about the compiler, see the user manual.

.SH DOCUMENTATION

Currently, the documentation for the system is
.TP 3
\--
the user manual
.TP 3
\--
this man page
.TP 3
\--
doc strings and online help built into the SBCL executable
.PP

.SH SYSTEM REQUIREMENTS

Unlike its distinguished ancestor CMU CL, SBCL is currently only
supported on X86. Linux, FreeBSD, and OpenBSD ports are currently
available. It would probably be straightforward to port the CMU CL
support for SPARC or Alpha, or to port to NetBSD. Some work on a
port to the Alpha has been reported on the mailing lists; check
the archives (available from the home page at
<http://sbcl.sourceforge.net/>) for information.

As of version 0.6.8, SBCL requires on the order of 16Mb to run. In
some future version, this number could shrink significantly, since
large parts of the system are far from execution bottlenecks and could
reasonably be stored in compact byte compiled form. (CMU CL does this
routinely; the only reason SBCL doesn't currently do this is a
combination of bootstrapping technicalities and inertia.)

.SH ENVIRONMENT

.TP 10n
.BR SBCL_HOME
If this variable is set, it overrides the default directories for
files like "sbclrc" and "sbcl.core", so that instead of being searched
for in e.g. /etc/, /usr/local/etc/, /usr/lib/, and /usr/local/lib/, they
are searched for only in the directory named by SBCL_HOME. This is
intended to support users who wish to use their own version of SBCL
instead of the version which is currently installed as the system
default.
.PP

.SH FILES

/usr/lib/sbcl.core and /usr/local/lib/sbcl.core are the standard
locations for the standard SBCL core, unless overridden by the SBCL_HOME
variable.

/etc/sbclrc and /usr/local/etc/sbclrc are the standard locations for
system-wide SBCL initialization files, unless overridden by the
SBCL_HOME variable.

$HOME/.sbclrc is the standard location for a user's SBCL
initialization file.

.SH BUGS

Too numerous to list, alas. This section attempts to list the most
serious known bugs, and a reasonably representative sampling of
others. For more information on bugs, see the BUGS file in the
distribution.

It is possible to get in deep trouble by exhausting
memory. To plagiarize a sadly apt description of a language not
renowned for the production of bulletproof software, "[The current
SBCL implementation of] Common Lisp makes it harder for you to shoot
yourself in the foot, but when you do, the entire universe explodes."
.TP 3
\--
The system doesn't deal well with stack overflow.
.TP 3
\--
The SBCL system overcommits memory at startup. On typical Unix-alikes
like Linux and *BSD, this means that if the SBCL system turns out to
use more virtual memory than the system has available for it, other
processes to be killed randomly (!)
.PP

The facility for dumping a running Lisp image to disk gets confused
when run without the PURIFY option, and creates an unnecessarily large
core file (apparently representing memory usage up to the previous
high-water mark). Moreover, when the file is loaded, it confuses the
GC, so that thereafter memory usage can never be reduced below that
level.

The compiler is overaggressive about static typing, assuming that a
function's return type never changes. Thus compiling and loading a
file containing
(DEFUN FOO (X) NIL)
(DEFUN BAR (X) (IF (FOO X) 1 2))
(DEFUN FOO (X) (PLUSP X))
then running (FOO 1) gives 2 (because the compiler "knew"
that FOO's return type is NULL).

The compiler's handling of function return values unnecessarily
violates the "declarations are assertions" principle that it otherwise
adheres to. Using PROCLAIM or DECLAIM to specify the return type of a
function causes the compiler to believe you without checking. Thus
compiling a file containing
(DECLAIM (FTYPE (FUNCTION (T) NULL) SOMETIMES))
(DEFUN SOMETIMES (X) (ODDP X))
(DEFUN FOO (X) (IF (SOMETIMES X) 'THIS-TIME 'NOT-THIS-TIME))
then running (FOO 1) gives NOT-THIS-TIME, because the
never compiled code to check the declaration.

The TRACE facility can't be used on some kinds of functions.

SYMBOL-FUNCTION is much slower than you'd expect, being implemented
not as a slot access but as a search through the compiler/kernel
"globaldb" database.

CLOS (based on the PCL reference implementation) is quite slow.

There are many nagging pre-ANSIisms, e.g.
.TP 3
\--
CLOS (based on the PCL reference implementation) is incompletely
integrated into the system, so that e.g. SB-PCL::FIND-CLASS is a
different function than CL::FIND-CLASS. (This is less of a problem in
practice than the speed, but it's still distasteful.)
.TP 3
--
The ANSI-recommended idiom for creating a function which is only
sometimes expanded inline,
(DECLAIM (INLINE F))
(DEFUN F ...)
(DECLAIM (NOTINLINE F)),
doesn't do what you'd expect. (Instead, you have to declare the
function as SB-EXT:MAYBE-INLINE to get the desired effect.)
.TP 3
\--
The DYNAMIC-EXTENT declaration is not implemented, and is simply
ignored. (This is allowed by the ANSI spec, but can have a large
efficiency cost in some kinds of code.)
.TP 3
--
Compiling DEFSTRUCT in strange places (e.g. inside a DEFUN) doesn't
do anything like what it should.
.TP 3
\--
The symbol * is the name of a type similar to T. (It's used as part
of the implementation of compound types like (ARRAY * 1).)
.PP

.SH SUPPORT

Various information about SBCL is available at
<http://sbcl.sourceforge.net/>. The mailing lists there are the
recommended place to look for support.

.SH DISTRIBUTION

SBCL is a free implementation of Common Lisp derived from CMU CL. Both
sources and executables are freely available; this software is "as
is", and has no warranty of any kind. CMU and the authors assume no
responsibility for the consequences of any use of this software. See
the CREDITS file in the distribution for more information about
history, contributors and permissions.