X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=doc%2Fmanual%2Fbeyond-ansi.texinfo;h=2fc20c84bc2062484aaba9308fd8ee0cb502b41d;hb=7ea8aa1c9a049cbfb02f96fae84a80ed8f550d70;hp=0f1b27a3d9de057b707ca384bdb6e164e209a380;hpb=a145b87809a5f266cc96e6a6e0e97b4a225bed2f;p=sbcl.git diff --git a/doc/manual/beyond-ansi.texinfo b/doc/manual/beyond-ansi.texinfo index 0f1b27a..2fc20c8 100644 --- a/doc/manual/beyond-ansi.texinfo +++ b/doc/manual/beyond-ansi.texinfo @@ -2,176 +2,206 @@ @comment node-name, next, previous, up @chapter Beyond the ANSI Standard -SBCL is mostly an implementation of the ANSI standard for -Common Lisp. However, there's some important behavior which extends -or clarifies the standard, and various behavior which outright -violates the standard. - - -@menu -* Non-Conformance With The ANSI Standard:: -* Idiosyncrasies:: -* Extensions:: -@end menu - -@node Non-Conformance With The ANSI Standard -@comment node-name, next, previous, up -@section Non-Conformance With The ANSI Standard - -Essentially every type of non-conformance is considered a bug. (The -exceptions involve internal inconsistencies in the standard.) In SBCL -0.7.6, the master record of known bugs is in the @file{BUGS} file in -the distribution. Some highlight information about bugs may also be -found in the manual page. The recommended way to report bugs is -through the sbcl-help or sbcl-devel mailing lists. For mailing list -addresses, @xref{More SBCL Information}. - - -@node Idiosyncrasies -@comment node-name, next, previous, up -@section Idiosyncrasies - -The information in this section describes some of the ways that SBCL -deals with choices that the ANSI standard leaves to the -implementation. - -Declarations are generally treated as assertions. This general -principle, and its implications, and the bugs which still keep the -compiler from quite satisfying this principle, are discussed in -@ref{Compiler}. - -SBCL is essentially a compiler-only implementation of Common -Lisp. That is, for all but a few special cases, @code{eval} creates a -lambda expression, calls @code{compile} on the lambda expression to -create a compiled function, and then calls @code{funcall} on the -resulting function object. This is explicitly allowed by the ANSI -standard, but leads to some oddities, e.g. collapsing @code{functionp} -and @code{compiled-function-p} into the same predicate. - -@findex defconstant -SBCL is quite strict about ANSI's definition of -@code{defconstant}. ANSI says that doing @code{defconstant} of the -same symbol more than once is undefined unless the new value is -@code{eql} to the old value. Conforming to this specification is a -nuisance when the ``constant'' value is only constant under some -weaker test like @code{string=} or @code{equal}. It's especially -annoying because, in SBCL, @code{defconstant} takes effect not only at -load time but also at compile time, so that just compiling and loading -reasonable code like -@lisp -(defconstant +foobyte+ '(1 4)) -@end lisp -runs into this undefined behavior. Many implementations of Common Lisp -try to help the programmer around this annoyance by silently accepting -the undefined code and trying to do what the programmer probably -meant. SBCL instead treats the undefined behavior as an error. Often -such code can be rewritten in portable ANSI Common Lisp which has the -desired behavior. E.g., the code above can be given an exactly -defined meaning by replacing @code{defconstant} either with -@code{defparameter} or with a customized macro which does the right -thing, possibly along the lines of the @code{defconstant-eqx} macro -used internally in the implementation of SBCL itself. In -circumstances where this is not appropriate, the programmer can handle -the condition type @code{sb-ext:defconstant-uneql}, and choose either -the @command{continue} or @command{abort} restart as appropriate. - -SBCL gives style warnings about various kinds of perfectly legal code, -e.g. - -@itemize - -@item -@code{defmethod} without a preceding @code{defgeneric}; - -@item -multiple @code{defun}s of the same symbol in different units; - -@item -special variables not named in the conventional @code{*foo*} style, -and lexical variables unconventionally named in the @code{*foo*} style - -@end itemize - -This causes friction with people who point out that other ways of -organizing code (especially avoiding the use of @code{defgeneric}) are -just as aesthetically stylish. However, these warnings should be read -not as ``warning, bad aesthetics detected, you have no style'' but -``warning, this style keeps the compiler from understanding the code -as well as you might like.'' That is, unless the compiler warns about -such conditions, there's no way for the compiler to warn about some -programming errors which would otherwise be easy to overlook. (Related -bug: The warning about multiple @code{defun}s is pointlessly annoying -when you compile and then load a function containing @code{defun} -wrapped in @code{eval-when}, and ideally should be suppressed in that -case, but still isn't as of SBCL 0.7.6.) - - -@node Extensions -@comment node-name, next, previous, up -@section Extensions - SBCL is derived from CMUCL, which implements many extensions to the ANSI standard. SBCL doesn't support as many extensions as CMUCL, but it still has quite a few. @xref{Contributed Modules}. - @menu -* Things Which Might Be In The Next ANSI Standard:: +* Garbage Collection:: +* Metaobject Protocol:: * Support For Unix:: * Customization Hooks for Users:: * Tools To Help Developers:: -* Interface To Low-Level SBCL Implementation:: +* Resolution of Name Conflicts:: * Stale Extensions:: * Efficiency Hacks:: @end menu -@node Things Which Might Be In The Next ANSI Standard +@node Garbage Collection @comment node-name, next, previous, up -@subsection Things Which Might Be In The Next ANSI Standard - -SBCL provides extensive support for calling external C code, -@ref{Foreign Function Interface}. +@section Garbage Collection SBCL provides additional garbage collection functionality not specified by ANSI. Weak pointers allow references to objects to be -maintained without keeping them from being GCed (garbage -collected). And ``finalization'' hooks are available to cause code to -be executed when an object has been GCed. -@c - -SBCL supports @dfn{Gray streams}, user-overloadable CLOS classes whose -instances can be used as Lisp streams (e.g. passed as the first -argument to @code{format}). Additionally, the bundled contrib module -@dfn{sb-simple-streams} implements a subset of the Franz Allegro -simple-streams proposal. - -SBCL supports a MetaObject Protocol which is intended to be compatible +maintained without keeping them from being garbage collected, and +``finalization'' hooks are available to cause code to be executed when +an object has been garbage collected. Additionally users can specify +their own cleanup actions to be executed with garbage collection. + +@include fun-sb-ext-finalize.texinfo +@include fun-sb-ext-cancel-finalization.texinfo +@include fun-sb-ext-make-weak-pointer.texinfo +@include fun-sb-ext-weak-pointer-value.texinfo +@include var-sb-ext-star-after-gc-hooks-star.texinfo + +@node Metaobject Protocol +@comment node-name, next, previous, up +@section Metaobject Protocol + +SBCL supports a metaobject protocol which is intended to be compatible with AMOP; present exceptions to this (as distinct from current bugs) are: @itemize @item -the abstract @code{metaobject} class is not present in the class -hierarchy; - +@findex compute-effective-method +@findex sb-mop:compute-effective-method +@code{compute-effective-method} only returns one value, not two. + +There is no record of what the second return value was meant to +indicate, and apparently no clients for it. + @item -the @code{standard-object} and @code{funcallable-standard-object} -classes are disjoint; +@tindex generic-function +@tindex standard-generic-function +@tindex funcallable-standard-object +@tindex sb-mop:funcallable-standard-object +@tindex standard-object +@tindex function +The direct superclasses of @code{sb-mop:funcallable-standard-object} are +@code{(function standard-object)}, not @code{(standard-object function)}. + +This is to ensure that the @code{standard-object} class is the last of +the standardized classes before @code{t} appearing in the class +precedence list of @code{generic-function} and +@code{standard-generic-function}, as required by section 1.4.4.5 of the +ANSI specification. @item -@code{compute-effective-method} only returns one value, not two; - +@findex ensure-generic-function +@findex generic-function-declarations +@findex sb-mop:generic-function-declarations +the arguments @code{:declare} and @code{:declarations} to +@code{ensure-generic-function} are both accepted, with the leftmost +argument defining the declarations to be stored and returned by +@code{generic-function-declarations}. + +Where AMOP specifies @code{:declarations} as the keyword argument to +@code{ensure-generic-function}, the Common Lisp standard specifies +@code{:declare}. Portable code should use @code{:declare}. + +@item +@findex validate-superclass +@findex finalize-inheritance +@findex sb-mop:validate-superclass +@findex sb-mop:finalize-inheritance +@tindex standard-class +@tindex funcallable-standard-class +@tindex sb-mop:funcallable-standard-class +@tindex function +@findex sb-mop:class-prototype +@findex class-prototype +although SBCL obeys the requirement in AMOP that +@code{validate-superclass} should treat @code{standard-class} and +@code{funcallable-standard-class} as compatible metaclasses, we +impose an additional requirement at class finalization time: a class +of metaclass @code{funcallable-standard-class} must have +@code{function} in its superclasses, and a class of metaclass +@code{standard-class} must not. + +@findex typep +@findex class-of +@findex subtypep +After a class has been finalized, it is associated with a class +prototype which is accessible by a standard mop function +@code{sb-mop:class-prototype}. The user can then ask whether this +object is a @code{function} or not in several different ways: whether it +is a function according to @code{typep}; whether its @code{class-of} is +@code{subtypep} @code{function}, or whether @code{function} appears in +the superclasses of the class. The additional consistency requirement +comes from the desire to make all of these answers the same. + +The following class definitions are bad, and will lead to errors +either immediately or if an instance is created: +@lisp +(defclass bad-object (funcallable-standard-object) + () + (:metaclass standard-class)) +@end lisp +@lisp +(defclass bad-funcallable-object (standard-object) + () + (:metaclass funcallable-standard-class)) +@end lisp +The following definition is acceptable: +@lisp +(defclass mixin () + ((slot :initarg slot))) +(defclass funcallable-object (funcallable-standard-object mixin) + () + (:metaclass funcallable-standard-class)) +@end lisp +and leads to a class whose instances are funcallable and have one slot. + +@tindex funcallable-standard-object +@tindex sb-mop:funcallable-standard-object +Note that this requirement also applies to the class +@code{sb-mop:funcallable-standard-object}, which has metaclass +@code{sb-mop:funcallable-standard-class} rather than +@code{standard-class} as AMOP specifies. + +@item +the requirement that ``No portable class @math{C_p} may inherit, by +virtue of being a direct or indirect subclass of a specified class, any +slot for which the name is a symbol accessible in the +@code{common-lisp-user} package or exported by any package defined in +the ANSI Common Lisp standard.'' is interpreted to mean that the +standardized classes themselves should not have slots named by external +symbols of public packages. + +The rationale behind the restriction is likely to be similar to the ANSI +Common Lisp restriction on defining functions, variables and types named +by symbols in the Common Lisp package: preventing two independent pieces +of software from colliding with each other. + +@item +@findex slot-value-using-class +@findex sb-mop:slot-value-using-class +@findex (setf slot-value-using-class) +@findex (setf sb-mop:slot-value-using-class) +@findex slot-boundp-using-class +@findex sb-mop:slot-boundp-using-class +specializations of the @code{new-value} argument to @code{(setf +sb-mop:slot-value-using-class)} are not allowed: all user-defined +methods must have a specializer of the class @code{t}. + +This prohibition is motivated by a separation of layers: the +@code{slot-value-using-class} family of functions is intended for use in +implementing different and new slot allocation strategies, rather than +in performing application-level dispatching. Additionally, with this +requirement, there is a one-to-one mapping between metaclass, class and +slot-definition-class tuples and effective methods of @code{(setf +slot-value-using-class)}, which permits optimization of @code{(setf +slot-value-using-class)}'s discriminating function in the same manner as +for @code{slot-value-using-class} and @code{slot-boundp-using-class}. + +Note that application code may specialize on the @code{new-value} +argument of slot accessors. + @item -the system-supplied @code{:around} method for @code{compute-slots} -specialized on @code{funcallable-standard-class} does not respect the -requested order from a user-supplied primary method. +@findex defclass +@findex ensure-class +@findex ensure-class-using-class +@findex sb-mop:ensure-class +@findex sb-mop:ensure-class-using-class +@findex find-class +@findex class-name +the class named by the @code{name} argument to @code{ensure-class}, if +any, is only redefined if it is the proper name of that class; +otherwise, a new class is created. + +This is consistent with the description of @code{ensure-class} in AMOP +as the functional version of @code{defclass}, which has this behaviour; +however, it is not consistent with the weaker requirement in AMOP, which +states that any class found by @code{find-class}, no matter what its +@code{class-name}, is redefined. @end itemize @node Support For Unix @comment node-name, next, previous, up -@subsection Support For Unix +@section Support For Unix The UNIX command line can be read from the variable @code{sb-ext:*posix-argv*}. The UNIX environment can be queried with @@ -179,17 +209,35 @@ the @code{sb-ext:posix-getenv} function. @include fun-sb-ext-posix-getenv.texinfo -The SBCL system can be terminated with @code{sb-ext:quit}, (but see -notes in @ref{Threading} about the interaction between this feature and -sessions) optionally returning a specified numeric value to the -calling Unix process. The normal Unix idiom of terminating on end of -file on input is also supported. +External programs can be run with @code{sb-ext:run-program}. + +@include fun-sb-ext-run-program.texinfo -@include fun-sb-ext-quit.texinfo +@include fun-sb-ext-process-p.texinfo + +@include fun-sb-ext-process-input.texinfo + +@include fun-sb-ext-process-output.texinfo + +@include fun-sb-ext-process-error.texinfo + +@include fun-sb-ext-process-alive-p.texinfo + +@include fun-sb-ext-process-status.texinfo + +@include fun-sb-ext-process-wait.texinfo + +@include fun-sb-ext-process-exit-code.texinfo + +@include fun-sb-ext-process-core-dumped.texinfo + +@include fun-sb-ext-process-close.texinfo + +@include fun-sb-ext-process-kill.texinfo @node Customization Hooks for Users @comment node-name, next, previous, up -@subsection Customization Hooks for Users +@section Customization Hooks for Users The toplevel repl prompt may be customized, and the function that reads user input may be replaced completely. @@ -209,12 +257,12 @@ mechanisms as follows: @include fun-common-lisp-ed.texinfo @include var-sb-ext-star-ed-functions-star.texinfo -@node Tools To Help Developers +@node Tools To Help Developers @comment node-name, next, previous, up -@subsection Tools To Help Developers +@section Tools To Help Developers SBCL provides a profiler and other extensions to the ANSI @code{trace} -facility. For more information, see @ref{macro-common-lisp-trace}. +facility. For more information, see @ref{Macro common-lisp:trace}. The debugger supports a number of options. Its documentation is accessed by typing @kbd{help} at the debugger prompt. @xref{Debugger}. @@ -222,27 +270,20 @@ accessed by typing @kbd{help} at the debugger prompt. @xref{Debugger}. Documentation for @code{inspect} is accessed by typing @kbd{help} at the @code{inspect} prompt. -@node Interface To Low-Level SBCL Implementation -@comment node-name, next, previous, up -@subsection Interface To Low-Level SBCL Implementation - -SBCL has the ability to save its state as a file for later -execution. This functionality is important for its bootstrapping -process, and is also provided as an extension to the user. Note that -foreign libraries loaded via @code{load-shared-object} don't survive -this process; a core should not be saved in this case. - -@emph{FIXME: what should be done for foreign libraries?} - -@emph{FIXME: document load-shared-object somewhere - it's in -ffi.texinfo?} - -@include fun-sb-ext-save-lisp-and-die.texinfo +@node Resolution of Name Conflicts +@section Resolution of Name Conflicts +The ANSI standard (section 11.1.1.2.5) requires that name conflicts in +packages be resolvable in favour of any of the conflicting symbols. In +the interactive debugger, this is achieved by prompting for the symbol +in whose favour the conflict should be resolved; for programmatic use, +the @code{sb-ext:resolve-conflict} restart should be invoked with one +argument, which should be a member of the list returned by the condition +accessor @code{sb-ext:name-conflict-symbols}. @node Stale Extensions @comment node-name, next, previous, up -@subsection Stale Extensions +@section Stale Extensions SBCL has inherited from CMUCL various hooks to allow the user to tweak and monitor the garbage collection process. These are somewhat @@ -264,18 +305,18 @@ list. @node Efficiency Hacks @comment node-name, next, previous, up -@subsection Efficiency Hacks +@section Efficiency Hacks The @code{sb-ext:purify} function causes SBCL first to collect all -garbage, then to mark all uncollected objects as permanent, never -again attempting to collect them as garbage. This can cause a large -increase in efficiency when using a primitive garbage collector, or a -more moderate increase in efficiency when using a more sophisticated -garbage collector which is well suited to the program's memory usage -pattern. It also allows permanent code to be frozen at fixed -addresses, a precondition for using copy-on-write to share code -between multiple Lisp processes. it is less important with modern -generational garbage collectors. +garbage, then to mark all uncollected objects as permanent, never again +attempting to collect them as garbage. This can cause a large increase +in efficiency when using a primitive garbage collector, or a more +moderate increase in efficiency when using a more sophisticated garbage +collector which is well suited to the program's memory usage pattern. It +also allows permanent code to be frozen at fixed addresses, a +precondition for using copy-on-write to share code between multiple Lisp +processes. This is less important with modern generational garbage +collectors, but not all SBCL platforms use such a garbage collector. @include fun-sb-ext-purify.texinfo