1 @node Beyond the ANSI Standard
2 @comment node-name, next, previous, up
3 @chapter Beyond the ANSI Standard
5 SBCL is derived from CMUCL, which implements many extensions to the
6 ANSI standard. SBCL doesn't support as many extensions as CMUCL, but
7 it still has quite a few. @xref{Contributed Modules}.
10 * Garbage Collection::
11 * Metaobject Protocol::
13 * Customization Hooks for Users::
14 * Tools To Help Developers::
15 * Resolution of Name Conflicts::
20 @node Garbage Collection
21 @comment node-name, next, previous, up
22 @section Garbage Collection
24 SBCL provides additional garbage collection functionality not
25 specified by ANSI. Weak pointers allow references to objects to be
26 maintained without keeping them from being garbage collected, and
27 ``finalization'' hooks are available to cause code to be executed when
28 an object has been garbage collected. Additionally users can specify
29 their own cleanup actions to be executed with garbage collection.
31 @include fun-sb-ext-finalize.texinfo
32 @include fun-sb-ext-cancel-finalization.texinfo
33 @include fun-sb-ext-make-weak-pointer.texinfo
34 @include fun-sb-ext-weak-pointer-value.texinfo
35 @include var-sb-ext-star-after-gc-hooks-star.texinfo
37 @node Metaobject Protocol
38 @comment node-name, next, previous, up
39 @section Metaobject Protocol
41 SBCL supports a metaobject protocol which is intended to be compatible
42 with AMOP; present exceptions to this (as distinct from current bugs)
48 the abstract @code{metaobject} class is not present in the class
52 the @code{standard-object} and @code{funcallable-standard-object}
56 @code{compute-effective-method} only returns one value, not two;
59 the system-supplied @code{:around} method for @code{compute-slots}
60 specialized on @code{funcallable-standard-class} does not respect the
61 requested order from a user-supplied primary method.
65 @node Support For Unix
66 @comment node-name, next, previous, up
67 @section Support For Unix
69 The UNIX command line can be read from the variable
70 @code{sb-ext:*posix-argv*}. The UNIX environment can be queried with
71 the @code{sb-ext:posix-getenv} function.
73 @include fun-sb-ext-posix-getenv.texinfo
76 @node Customization Hooks for Users
77 @comment node-name, next, previous, up
78 @section Customization Hooks for Users
80 The toplevel repl prompt may be customized, and the function
81 that reads user input may be replaced completely.
82 @c <!-- FIXME but I don't currently remember how -->
84 The behaviour of @code{require} when called with only one argument is
85 implementation-defined. In SBCL, @code{require} behaves in the
88 @include fun-common-lisp-require.texinfo
89 @include var-sb-ext-star-module-provider-functions-star.texinfo
91 Although SBCL does not provide a resident editor, the @code{ed}
92 function can be customized to hook into user-provided editing
93 mechanisms as follows:
95 @include fun-common-lisp-ed.texinfo
96 @include var-sb-ext-star-ed-functions-star.texinfo
98 @node Tools To Help Developers
99 @comment node-name, next, previous, up
100 @section Tools To Help Developers
102 SBCL provides a profiler and other extensions to the ANSI @code{trace}
103 facility. For more information, see @ref{Macro common-lisp:trace}.
105 The debugger supports a number of options. Its documentation is
106 accessed by typing @kbd{help} at the debugger prompt. @xref{Debugger}.
108 Documentation for @code{inspect} is accessed by typing @kbd{help} at
109 the @code{inspect} prompt.
111 @node Resolution of Name Conflicts
112 @section Resolution of Name Conflicts
114 The ANSI standard (section 11.1.1.2.5) requires that name conflicts in
115 packages be resolvable in favour of any of the conflicting symbols. In
116 the interactive debugger, this is achieved by prompting for the symbol
117 in whose favour the conflict should be resolved; for programmatic use,
118 the @code{sb-ext:resolve-conflict} restart should be invoked with one
119 argument, which should be a member of the list returned by the condition
120 accessor @code{sb-ext:name-conflict-symbols}.
122 @node Stale Extensions
123 @comment node-name, next, previous, up
124 @section Stale Extensions
126 SBCL has inherited from CMUCL various hooks to allow the user to
127 tweak and monitor the garbage collection process. These are somewhat
128 stale code, and their interface might need to be cleaned up. If you
129 have urgent need of them, look at the code in @file{src/code/gc.lisp}
130 and bring it up on the developers' mailing list.
132 SBCL has various hooks inherited from CMUCL, like
133 @code{sb-ext:float-denormalized-p}, to allow a program to take
134 advantage of IEEE floating point arithmetic properties which aren't
135 conveniently or efficiently expressible using the ANSI standard. These
136 look good, and their interface looks good, but IEEE support is
137 slightly broken due to a stupid decision to remove some support for
138 infinities (because it wasn't in the ANSI spec and it didn't occur to
139 me that it was in the IEEE spec). If you need this stuff, take a look
140 at the code and bring it up on the developers' mailing
144 @node Efficiency Hacks
145 @comment node-name, next, previous, up
146 @section Efficiency Hacks
148 The @code{sb-ext:purify} function causes SBCL first to collect all
149 garbage, then to mark all uncollected objects as permanent, never again
150 attempting to collect them as garbage. This can cause a large increase
151 in efficiency when using a primitive garbage collector, or a more
152 moderate increase in efficiency when using a more sophisticated garbage
153 collector which is well suited to the program's memory usage pattern. It
154 also allows permanent code to be frozen at fixed addresses, a
155 precondition for using copy-on-write to share code between multiple Lisp
156 processes. This is less important with modern generational garbage
157 collectors, but not all SBCL platforms use such a garbage collector.
159 @include fun-sb-ext-purify.texinfo
161 The @code{sb-ext:truly-the} special form declares the type of the
162 result of the operations, producing its argument; the declaration is
163 not checked. In short: don't use it.
165 @include special-operator-sb-ext-truly-the.texinfo
167 The @code{sb-ext:freeze-type} declaration declares that a
168 type will never change, which can make type testing
169 (@code{typep}, etc.) more efficient for structure types.
171 The @code{sb-ext:constant-function} declaration specifies
172 that a function will always return the same value for the same
173 arguments, which may allow the compiler to optimize calls
174 to it. This is appropriate for functions like @code{sqrt}, but
175 is @emph{not} appropriate for functions like @code{aref},
176 which can change their return values when the underlying data are
178 @c <!-- FIXME: This declaration does not seem to be supported in the
179 @c current compiler. -->