chap-24.texi

@node System Construction
@chapter System Construction
@menu
* System Construction Concepts::
* System Construction Dictionary::
@end menu

@node System Construction Concepts
@section System Construction Concepts

@menu
* Loading::
* Features::
@end menu
@node Loading
@subsection Loading

To @symbolref{load, SYM} a @term{file} is to treat its contents as @term{code}
and @term{execute} that @term{code}.
The @term{file} may contain @newterm{source code} or @newterm{compiled code}.

A @term{file} containing @term{source code} is called a @newterm{source file}.
@term{Loading} a @term{source file} is accomplished essentially
by sequentially @term{reading}@sub{2} the @term{forms} in the file,
@i{evaluating} each immediately after it is @term{read}.

A @term{file} containing @term{compiled code} is called a @newterm{compiled file}.
@term{Loading} a @term{compiled file} is similar to @term{loading} a @term{source file},
except that the @term{file} does not contain text but rather an
@term{implementation-dependent} representation of pre-digested @term{expressions}
created by the @term{compiler}.  Often, a @term{compiled file} can be @term{loaded}
more quickly than a @term{source file}.
See @ref{Compilation}.

The way in which a @term{source file} is distinguished from a @term{compiled file}
is @term{implementation-dependent}.


@node Features
@subsection Features

A @newterm{feature} is an aspect or attribute
of @clisp{},
of the @term{implementation},
or of the @term{environment}.
A @term{feature} is identified by a @term{symbol}.

A @term{feature} is said to be @newterm{present} in a @term{Lisp image}
if and only if the @term{symbol} naming it is an @term{element} of the
@term{list} held by @thevariable{*features*},
which is called the @newterm{features list}.

@node Feature Expressions
@subsubsection Feature Expressions
Boolean combinations of @term{features}, called
@cindex feature expression
@dfn{feature expressions},
are used by the @f{#+} and @f{#-} @term{reader macros} in order to
direct conditional @term{reading} of @term{expressions} by the @term{Lisp reader}.

The rules for interpreting a @term{feature expression} are as follows:


@table @asis

@item @id{@term{feature}}


If a @term{symbol} naming a @term{feature} is used as a @term{feature expression},
the @term{feature expression} succeeds if that @term{feature} is @term{present};
otherwise it fails.

@item @id{@f{(not @param{feature-conditional})}}


A @t{not} @term{feature expression} succeeds
if its argument @param{feature-conditional} fails;
otherwise, it succeeds.

@item @id{@f{(and @starparam{feature-conditional})}}


An @t{and} @term{feature expression} succeeds
if all of its argument @param{feature-conditionals} succeed;
otherwise, it fails.

@item @id{@f{(or @starparam{feature-conditional})}}


An @t{or} @term{feature expression} succeeds
if any of its argument @param{feature-conditionals} succeed;
otherwise, it fails.
@end table


@node Examples of Feature Expressions
@subsubsection Examples of Feature Expressions

in @term{implementation} A, the @term{features} @f{spice} and @f{perq} are @term{present},
but the @term{feature} @f{lispm} is not @term{present};
in @term{implementation} B, the feature @f{lispm} is @term{present},
but the @term{features} @f{spice} and @f{perq} are
not @term{present};
and
in @term{implementation} C, none of the features @f{spice}, @tt{lispm}, or @f{perq} are
@term{present}.
@Thenextfigure{}@spc{}shows some sample @term{expressions}, and how they would be
@term{read}@sub{2} in these @term{implementations}.


@float Figure,fig24.1
@cartouche
@multitable{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx}{xxxxxxxxxxxxxxxxxxxxxxxxxxxxx}

@item @f{(cons #+spice "Spice" #-spice "Lispm" x)} @tab
@item @quad{} in @term{implementation} A @mat{@ldots{}} @tab @f{(CONS "Spice" X)}
@item @quad{} in @term{implementation} B @mat{@ldots{}} @tab @f{(CONS "Lispm" X)}
@item @quad{} in @term{implementation} C @mat{@ldots{}} @tab @f{(CONS "Lispm" X)}
@item @f{(cons #+spice "Spice" #+LispM "Lispm" x)} @tab
@item @quad{} in @term{implementation} A @mat{@ldots{}} @tab @f{(CONS "Spice" X)}
@item @quad{} in @term{implementation} B @mat{@ldots{}} @tab @f{(CONS "Lispm" X)}
@item @quad{} in @term{implementation} C @mat{@ldots{}} @tab @f{(CONS X)}
@item @f{(setq a '(1 2 #+perq 43 #+(not perq) 27))} @tab
@item @quad{} in @term{implementation} A @mat{@ldots{}} @tab @f{(SETQ A '(1 2 43))}
@item @quad{} in @term{implementation} B @mat{@ldots{}} @tab @f{(SETQ A '(1 2 27))}
@item @quad{} in @term{implementation} C @mat{@ldots{}} @tab @f{(SETQ A '(1 2 27))}
@item @f{(let ((a 3) #+(or spice lispm) (b 3)) (foo a))} @tab
@item @quad{} in @term{implementation} A @mat{@ldots{}} @tab @f{(LET ((A 3) (B 3)) (FOO A))}
@item @quad{} in @term{implementation} B @mat{@ldots{}} @tab @f{(LET ((A 3) (B 3)) (FOO A))}
@item @quad{} in @term{implementation} C @mat{@ldots{}} @tab @f{(LET ((A 3)) (FOO A))}
@item @f{(cons #+Lispm "#+Spice" #+Spice "foo" #-(or Lispm Spice) 7 x)} @tab
@item @quad{} in @term{implementation} A @mat{@ldots{}} @tab @f{(CONS "foo" X)}
@item @quad{} in @term{implementation} B @mat{@ldots{}} @tab @f{(CONS "#+Spice" X)}
@item @quad{} in @term{implementation} C @mat{@ldots{}} @tab @f{(CONS 7 X)}
@end multitable
@end cartouche
@caption{Features examples}
@end float


@node System Construction Dictionary
@section System Construction Dictionary

@menu
* compile-file::
* compile-file-pathname::
* load::
* with-compilation-unit::
* *features*::
* *compile-file-pathname*; *compile-file-truename*::
* *load-pathname*; *load-truename*::
* *compile-print*; *compile-verbose*::
* *load-print*; *load-verbose*::
* *modules*::
* provide; require::
@end menu

@node compile-file
@syindexanchor{compile-file, SYM}
@subsection compile-file (Function)
@cindex compile-file


@subsubheading Syntax:

@DefunWithValuesNewline{compile-file, input-file @keyparam{} @vtop{@hbox{output-file verbose} @hbox{print external-format}}, output-truename\, warnings-p\, failure-p}

@subsubheading Arguments and Values:

@param{input-file}---a @term{pathname designator}.
(Default fillers for unspecified components are taken from
@symbolref{*default-pathname-defaults*, SYM}.)

@param{output-file}---a @term{pathname designator}.
@Default{@term{implementation-defined}}

@param{verbose}---a @term{generalized boolean}.
@Default{@thevalueof{*compile-verbose*}}

@param{print}---a @term{generalized boolean}.
@Default{@thevalueof{*compile-print*}}


@param{external-format}---an @term{external file format designator}.
@Default{@kwd{default}}

@param{output-truename}---a @term{pathname} (the @symbolref{truename, SYM} of the output @term{file}),
or @nil{}.

@param{warnings-p}---a @term{generalized boolean}.

@param{failure-p}---a @term{generalized boolean}.



@subsubheading Description:

@symbolref{compile-file, SYM} transforms the contents of the file specified
by @param{input-file} into @term{implementation-dependent} binary data
which are placed in the file specified by @param{output-file}.

The @term{file} to which @param{input-file} refers should be a @term{source file}.
@param{output-file} can be used to specify an output @term{pathname};
the actual @term{pathname} of the @term{compiled file}
to which @term{compiled code} will be output
is computed as if by calling @symbolref{compile-file-pathname, SYM}.

If @param{input-file} or @param{output-file} is a @term{logical pathname},
it is translated into a @term{physical pathname} as if by calling
@symbolref{translate-logical-pathname, SYM}.

If @param{verbose} is @term{true},
@symbolref{compile-file, SYM} prints a message in the form of a comment
(@ie{} with a leading @term{semicolon})
to @term{standard output} indicating what @term{file} is being @term{compiled}
and other useful information.
If @param{verbose} is @term{false},
@symbolref{compile-file, SYM} does not print
this information.

If @param{print} is @term{true},
information about @term{top level forms} in the file being
compiled is printed to @term{standard output}.
Exactly what is printed is @term{implementation-dependent},
but nevertheless some information is printed.
If @param{print} is @nil{}, no information is printed.

The @param{external-format} specifies the @term{external file format}
to be used when opening the @term{file}; see the @term{function} @ref{open}.
@symbolref{compile-file, SYM} and @symbolref{load, SYM} must cooperate in such a way that
the resulting @term{compiled file} can be @term{loaded}
without specifying an @term{external file format} anew; see the @term{function} @ref{load}.

@symbolref{compile-file, SYM} binds @symbolref{*readtable*, SYM} and @symbolref{*package*, SYM}
to the values they held before processing the file.

@symbolref{*compile-file-truename*, SYM} is bound by @symbolref{compile-file, SYM}
to hold the @term{truename} of the @term{pathname} of the file being compiled.

@symbolref{*compile-file-pathname*, SYM} is bound by @symbolref{compile-file, SYM}
to hold a @term{pathname} denoted by the first argument to @symbolref{compile-file, SYM},
merged against the defaults;
that is, @f{(pathname (merge-pathnames @param{input-file}))}.

The compiled @term{functions} contained in the @term{compiled file} become available
for use when the @term{compiled file} is @term{loaded} into Lisp.
Any function definition that is processed by the
compiler, including @f{#'(lambda ...)} forms and local function
definitions made by @symbolref{flet, SYM}, @symbolref{labels, SYM} and @symbolref{defun, SYM} forms,
result in an @term{object} @oftype{compiled-function}.

The @term{primary value} returned by @symbolref{compile-file, SYM}, @param{output-truename},
is the @symbolref{truename, SYM} of the output file, or @nil{}@spc{}if the file could not be created.

The @term{secondary value}, @param{warnings-p}, is @term{false}
if no @term{conditions} @oftype{error} or @symbolref{warning, SYM}
were detected by the compiler, and @term{true} otherwise.

The @term{tertiary value}, @param{failure-p}, is @term{false}
if no @term{conditions} @oftype{error} or @symbolref{warning, SYM}
(other than @symbolref{style-warning, SYM})
were detected by the compiler, and @term{true} otherwise.

For general information about how @term{files} are processed by the @term{file compiler},
see @ref{File Compilation}.


@term{Programs} to be compiled by the @term{file compiler} must only contain
@term{externalizable objects}; for details on such @term{objects},
see @ref{Literal Objects in Compiled Files}.
For information on how to extend the set of @term{externalizable objects},
see the @term{function} @ref{Additional Constraints on Externalizable Objects}.

@subsubheading Affected By:
@symbolref{*error-output*, SYM},
@symbolref{*standard-output*, SYM}, @symbolref{*compile-verbose*, SYM}, @symbolref{*compile-print*, SYM}

The computer's file system.
@subsubheading Exceptional Situations:

For information about errors detected during the compilation process,
see @ref{Exceptional Situations in the Compiler}.

An error @oftype{file-error} might be signaled if
@tt{(wild-pathname-p @param{input-file})} returns true.

If either the attempt to open the @term{source file} for input
or the attempt to open the @term{compiled file} for output
fails,
an error @oftype{file-error} is signaled.

@subsubheading See Also:

@ref{compile},
@ref{declare},
@ref{eval-when},
@ref{pathname (System Class)},
@ref{logical-pathname (System Class)},
@ref{File System Concepts},
@ref{Pathnames as Filenames}



@node compile-file-pathname
@syindexanchor{compile-file-pathname, SYM}
@subsection compile-file-pathname (Function)
@cindex compile-file-pathname



@subsubheading Syntax:

@DefunWithValues{compile-file-pathname, input-file @keyparam{} output-file @allowotherkeys{}, pathname}

@subsubheading Arguments and Values:

@param{input-file}---a @term{pathname designator}.
(Default fillers for unspecified components are taken from
@symbolref{*default-pathname-defaults*, SYM}.)

@param{output-file}---a @term{pathname designator}.
@Default{@term{implementation-defined}}

@param{pathname}---a @term{pathname}.

@subsubheading Description:

Returns the @term{pathname} that @symbolref{compile-file, SYM} would write into,
if given the same arguments.

The defaults for the @param{output-file}
are taken from the @term{pathname}
that results from merging the @param{input-file}
with @thevalueof{*default-pathname-defaults*},
except that the type component
should default to the appropriate
@term{implementation-defined} default type for @term{compiled files}.

If @param{input-file} is a @term{logical pathname} and @param{output-file}
is unsupplied, the result is a @term{logical pathname}.
If @param{input-file} is a @term{logical pathname},
it is translated into a physical pathname as if by calling
@symbolref{translate-logical-pathname, SYM}.
If @param{input-file} is a @term{stream},
the @term{stream} can be either open or closed.
@symbolref{compile-file-pathname, SYM} returns the same @term{pathname} after a
file is closed as it did when the file was open.
It is an error if @param{input-file} is a @term{stream} that is
created with @symbolref{make-two-way-stream, SYM}, @symbolref{make-echo-stream, SYM},
@symbolref{make-broadcast-stream, SYM}, @symbolref{make-concatenated-stream, SYM},
@symbolref{make-string-input-stream, SYM}, @symbolref{make-string-output-stream, SYM}.

If an implementation supports additional keyword arguments to @symbolref{compile-file, SYM},
@symbolref{compile-file-pathname, SYM} must accept the same arguments.

@subsubheading Examples:

See @symbolref{logical-pathname-translations, SYM}.

@subsubheading Exceptional Situations:

An error @oftype{file-error} might be signaled if either @param{input-file} or
@param{output-file} is @term{wild}.

@subsubheading See Also:

@ref{compile-file},
@ref{pathname (System Class)},
@ref{logical-pathname (System Class)},
@ref{File System Concepts},
@ref{Pathnames as Filenames}




@node load
@syindexanchor{load, SYM}
@subsection load (Function)
@cindex load


@subsubheading Syntax:

@DefunWithValuesNewline{load, filespec @keyparam{} @vtop{@hbox{verbose print} @hbox{if-does-not-exist external-format}}, generalized-boolean}

@subsubheading Arguments and Values:

@param{filespec}---a @term{stream}, or a @term{pathname designator}.
@Default{taken from @symbolref{*default-pathname-defaults*, SYM}}

@param{verbose}---a @term{generalized boolean}.
@Default{@thevalueof{*load-verbose*}}

@param{print}---a @term{generalized boolean}.
@Default{@thevalueof{*load-print*}}

@param{if-does-not-exist}---a @term{generalized boolean}.
@Default{@term{true}}

@param{external-format}---an @term{external file format designator}.
@Default{@kwd{default}}

@param{generalized-boolean}---a @term{generalized boolean}.

@subsubheading Description:

@symbolref{load, SYM} @term{loads} the @term{file} named by @param{filespec}
into the @Lisp{}@spc{}environment.

The manner in which a @term{source file}
is distinguished from a @term{compiled file} is @term{implementation-dependent}.
If the file specification is not complete and both a @term{source file} and a
@term{compiled file} exist which might match,
then which of those files @symbolref{load, SYM} selects is @term{implementation-dependent}.

If @param{filespec} is a @term{stream},
@symbolref{load, SYM} determines what kind of @term{stream} it is
and loads directly from the @term{stream}.
If @param{filespec} is a @term{logical pathname},
it is translated into a @term{physical pathname}
as if by calling @symbolref{translate-logical-pathname, SYM}.

@symbolref{load, SYM} sequentially executes each @term{form} it encounters
in the @term{file} named by @param{filespec}.
If the @term{file} is a @term{source file}
and the @term{implementation} chooses to perform @term{implicit compilation},
@symbolref{load, SYM} must recognize @term{top level forms}
as described in @ref{Processing of Top Level Forms}
and arrange for each @term{top level form} to be executed
before beginning @term{implicit compilation} of the next.
(Note, however, that processing of @symbolref{eval-when, SYM} @term{forms}
by @symbolref{load, SYM} is controlled by the @kwd{execute} situation.)

If @param{verbose} is @term{true},
@symbolref{load, SYM} prints a message in the form of a comment
(@ie{} with a leading @term{semicolon})
to @term{standard output} indicating what @term{file} is being @term{loaded}
and other useful information.
If @param{verbose} is @term{false},
@symbolref{load, SYM} does not print this information.

If @param{print} is @term{true},
@symbolref{load, SYM} incrementally prints information to @term{standard output}
showing the progress of the @term{loading} process.
For a @term{source file},
this information might mean printing the @term{values}
@term{yielded} by each @term{form} in the @term{file}
as soon as those @term{values} are returned.
For a @term{compiled file},
what is printed might not reflect precisely the contents of the @term{source file},
but some information is generally printed.
If @param{print} is @term{false},
@symbolref{load, SYM} does not print this information.

If the file named by @param{filespec} is successfully loaded,
@symbolref{load, SYM} returns @term{true}.

@reviewer{Loosemore: What happens if the file cannot be loaded for some reason other
than that it doesn't exist?} @editornote{KMP: i.e., can it return NIL? must it?}

If the file does not exist,
the specific action taken depends on @param{if-does-not-exist}:
if it is @nil{}, @symbolref{load, SYM} returns @nil{};
otherwise, @symbolref{load, SYM} signals an error.

The @param{external-format} specifies the @term{external file format}
to be used when opening the @term{file} (see the @term{function} @ref{open}),
except that when the @term{file} named by @param{filespec} is a @term{compiled file},
the @param{external-format} is ignored.
@symbolref{compile-file, SYM} and @symbolref{load, SYM} cooperate
in an @term{implementation-dependent} way to assure
the preservation of the @term{similarity} of @term{characters}
referred to in the @term{source file}
at the time the @term{source file} was processed by the @term{file compiler}
under a given @term{external file format},
regardless of the value of @param{external-format}
at the time the @term{compiled file} is @term{loaded}.

@symbolref{load, SYM} binds @symbolref{*readtable*, SYM} and @symbolref{*package*, SYM}
to the values they held before @term{loading} the file.

@symbolref{*load-truename*, SYM} is @term{bound} by @symbolref{load, SYM} to hold
the @term{truename} of the @term{pathname} of the file being @term{loaded}.

@symbolref{*load-pathname*, SYM} is @term{bound} by @symbolref{load, SYM} to hold
a @term{pathname} that represents @param{filespec} merged against the defaults.
That is, @tt{(pathname (merge-pathnames @param{filespec}))}.

@subsubheading Examples:

@lisp
;Establish a data file...
 (with-open-file (str "data.in" :direction :output :if-exists :error)
   (print 1 str) (print '(setq a 888) str) t)
@EV{} T
 (load "data.in") @EV{} @term{true}
 a @EV{} 888
 (load (setq p (merge-pathnames "data.in")) :verbose t)
; Loading contents of file /fred/data.in
; Finished loading /fred/data.in
@EV{} @term{true}
 (load p :print t)
; Loading contents of file /fred/data.in
;  1
;  888
; Finished loading /fred/data.in
@EV{} @term{true}
@end lisp


@medbreak{}
@lisp
 ;----[Begin file SETUP]----
 (in-package "MY-STUFF")
 (defmacro compile-truename () `',*compile-file-truename*)
 (defvar *my-compile-truename* (compile-truename) "Just for debugging.")
 (defvar *my-load-pathname* *load-pathname*)
 (defun load-my-system ()
   (dolist (module-name '("FOO" "BAR" "BAZ"))
     (load (merge-pathnames module-name *my-load-pathname*))))
 ;----[End of file SETUP]----


 (load "SETUP")
 (load-my-system)
@end lisp


@subsubheading Affected By:

The implementation, and the host computer's file system.

@subsubheading Exceptional Situations:

If @kwd{if-does-not-exist} is supplied and is @term{true}, or is not supplied,
@symbolref{load, SYM} signals an error @oftype{file-error} if the file named by
@param{filespec} does not exist,
or if the @term{file system} cannot perform the requested operation.

An error @oftype{file-error} might be signaled if
@f{(wild-pathname-p @param{filespec})} returns @term{true}.

@subsubheading See Also:

@ref{error (Function)},
@ref{merge-pathnames},
@ref{*load-verbose*},
@ref{*default-pathname-defaults*},
@ref{pathname (System Class)},
@ref{logical-pathname (System Class)},
@ref{File System Concepts},
@ref{Pathnames as Filenames}



@node with-compilation-unit
@syindexanchor{with-compilation-unit, SYM}
@subsection with-compilation-unit (Macro)
@cindex with-compilation-unit



@subsubheading Syntax:

@DefmacWithValues{with-compilation-unit, @paren{@interleave{@down{option}}} @starparam{form}, @starparam{result}}

@auxbnf{option, @kwd{override} override}

@subsubheading Arguments and Values:

@param{override}---a @term{generalized boolean}; @eval{}.
@Default{@nil{}}

@param{forms}---an @term{implicit progn}.

@param{results}---the @term{values} returned by the @term{forms}.

@subsubheading Description:

Executes @param{forms} from left to right.
Within the @term{dynamic environment} of @symbolref{with-compilation-unit, SYM},
actions deferred by the compiler until the end of compilation will be
deferred until the end of the outermost call to @symbolref{with-compilation-unit, SYM}.

The set of @i{options} permitted may be extended by the implementation,
but the only @term{standardized} keyword is @kwd{override}.

If nested dynamically only the outer call to
@symbolref{with-compilation-unit, SYM} has any effect unless the value
associated with @kwd{override} is @term{true}, in which case warnings are
deferred only to the end of the innermost call for which @param{override} is @term{true}.

The function @symbolref{compile-file, SYM}
provides the effect of

@lisp
 (with-compilation-unit (:override nil) ...)
@end lisp

around its @term{code}.

Any @term{implementation-dependent} extensions can only be provided as the
result of an explicit programmer request by use of an
@term{implementation-dependent} keyword.  @term{Implementations} are forbidden
from attaching additional meaning to a use of this macro which involves either
no keywords or just the keyword @kwd{override}.

@subsubheading Examples:

If an @term{implementation} would normally defer certain kinds of warnings,
such as warnings about undefined functions, to the end of a compilation
unit (such as a @term{file}), the following example shows how to cause those
warnings to be deferred to the end of the compilation of several files.

@lisp
 (defun compile-files (&rest files)
   (with-compilation-unit ()
     (mapcar #'(lambda (file) (compile-file file)) files)))

 (compile-files "A" "B" "C")
@end lisp


Note however that if the implementation does not normally defer any warnings,
use of @symbolref{with-compilation-unit, SYM} might not have any effect.

@subsubheading See Also:

@ref{compile}, @ref{compile-file}



@node *features*
@syindexanchor{*features*, SYM}
@subsection *features* (Variable)
@cindex *features*


@subsubheading Value Type:

a @term{proper list}.

@subsubheading Initial Value:

@term{implementation-dependent}.

@subsubheading Description:

@Thevalueof{*features*} is called the @term{features list}.
It is a @term{list} of @term{symbols}, called @term{features},
that correspond to some aspect of the @term{implementation} or @term{environment}.

Most @term{features} have @term{implementation-dependent} meanings;
The following meanings have been assigned to feature names:


@table @asis

@item @id{@kwd{cltl1}}


If present, indicates that the @code{LISP} @term{package} @term{purports to conform}
to the 1984 specification @CLtL{}.
It is possible, but not required, for a @term{conforming implementation}
to have this feature because this specification specifies that
its @term{symbols} are to be in the @code{COMMON-LISP} @term{package},
not the @code{LISP} package.

@item @id{@kwd{cltl2}}


If present, indicates that the implementation @term{purports to conform}
to @CLtLTwo{}.
This feature must not be present in any @term{conforming implementation},
since conformance to that document is not compatible with conformance
to this specification.
The name, however, is reserved by this specification in order to help
programs distinguish implementations which conform to that document
from implementations which conform to this specification.

@item @id{@kwd{ieee-floating-point}}


If present, indicates that the implementation @term{purports to conform}
to the requirements of @IEEEFloatingPoint{}.

@item @id{@kwd{x3j13}}


If present, indicates that the implementation conforms to some
particular working draft of this specification,
or to some subset of features that approximates a belief about
what this specification might turn out to contain.
A @term{conforming implementation} might or might not contain
such a feature.
(This feature is intended primarily as a stopgap in order to
provide implementors something to use prior to the availability
of a draft standard, in order to discourage them from introducing
the @kwd{draft-ansi-cl} and @kwd{ansi-cl} @term{features} prematurely.)

@item @id{@kwd{draft-ansi-cl}}


If present, indicates that the @term{implementation}
@term{purports to conform} to the first full draft of this specification,
which went to public review in 1992.
A @term{conforming implementation}
which has the @kwd{draft-ansi-cl-2} or @kwd{ansi-cl} @term{feature}
is not permitted to retain the @kwd{draft-ansi-cl} @term{feature}
since incompatible changes were made subsequent to the first draft.

@item @id{@kwd{draft-ansi-cl-2}}


If present, indicates that a second full draft of this specification
has gone to public review, and that the @term{implementation}
@term{purports to conform} to that specification.
(If additional public review drafts are produced, this keyword
will continue to refer to the second draft, and additional keywords
will be added to identify conformance with such later drafts.
As such, the meaning of this keyword can be relied upon not to
change over time.)
A @term{conforming implementation} which has the @kwd{ansi-cl}
@term{feature} is only permitted to retain the @kwd{draft-ansi-cl}
@term{feature} if the finally approved standard is not incompatible
with the draft standard.

@item @id{@kwd{ansi-cl}}


If present, indicates that this specification has been adopted by ANSI
as an official standard, and that the @term{implementation}
@term{purports to conform}.

@item @id{@kwd{common-lisp}}


This feature must appear in @symbolref{*features*, SYM} for any implementation that
has one or more of the features @kwd{x3j13}, @kwd{draft-ansi-cl},
or @kwd{ansi-cl}.  It is intended that it should also appear in
implementations which have the features @kwd{cltl1} or @kwd{cltl2},
but this specification cannot force such behavior.  The intent is
that this feature should identify the language family named ``Common Lisp,''
rather than some specific dialect within that family.
@end table


@subsubheading See Also:

@ref{Use of Read-Time Conditionals},
@ref{Standard Macro Characters}

@subsubheading Notes:

@Thevalueof{*features*} is used by the @f{#+} and @f{#-} reader syntax.

@term{Symbols} in the @term{features list} may be in any @term{package},
but in practice they are generally in the @code{KEYWORD} @term{package}.
This is because @code{KEYWORD} is the @term{package} used by default
when @term{reading}@sub{2} @term{feature expressions}
in the @f{#+} and @f{#-} @term{reader macros}.
@term{Code} that needs to name a @term{feature}@sub{2} in a
@term{package} @mat{P} (other than @code{KEYWORD}) can do so
by making explicit use of a @term{package prefix} for @mat{P},
but note that such @term{code} must also assure that the @term{package} @mat{P}
exists in order for the @term{feature expression} to be @term{read}@sub{2}---even
in cases where the @term{feature expression} is expected to fail.

It is generally considered wise for an @term{implementation} to include
one or more @term{features} identifying the specific @term{implementation},
so that conditional expressions can be written which distinguish
idiosyncrasies of one @term{implementation} from those of another.
Since features are normally @term{symbols} in the @code{KEYWORD} @term{package}
where name collisions might easily result, and since no uniquely defined mechanism
is designated for deciding who has the right to use which @term{symbol} for
what reason, a conservative strategy is to prefer names derived from
one's own company or product name, since those names are often trademarked
and are hence less likely to be used unwittingly by another @term{implementation}.


@node *compile-file-pathname*; *compile-file-truename*
@syindexanchor{*compile-file-pathname*, SYM}
@syindexanchor{*compile-file-truename*, SYM}
@subsection *compile-file-pathname*, *compile-file-truename* (Variable)
@cindex *compile-file-pathname*
@cindex *compile-file-truename*



@subsubheading Value Type:

@Thevalueof{*compile-file-pathname*} must always be a @term{pathname}          or @nil{}.
@Thevalueof{*compile-file-truename*} must always be a @term{physical pathname} or @nil{}.

@subsubheading Initial Value:

@nil{}.

@subsubheading Description:

During a call to @symbolref{compile-file, SYM},
@symbolref{*compile-file-pathname*, SYM} is @term{bound} to
the @term{pathname} denoted by the first argument to @symbolref{compile-file, SYM},
merged against the defaults;
that is, it is @term{bound} to @f{(pathname (merge-pathnames @param{input-file}))}.
During the same time interval,
@symbolref{*compile-file-truename*, SYM} is @term{bound} to
the @term{truename} of the @term{file} being @term{compiled}.

At other times, the @term{value} of these @term{variables} is @nil{}.

If a @term{break loop} is entered while @symbolref{compile-file, SYM} is ongoing,
it is @term{implementation-dependent} whether these @term{variables} retain
the @term{values} they had just prior to entering the @term{break loop}
or whether they are @term{bound} to @nil{}.

The consequences are unspecified if
an attempt is made to @term{assign} or @term{bind} either of these @term{variables}.

@subsubheading Affected By:

The @term{file system}.

@subsubheading See Also:

@ref{compile-file}



@node *load-pathname*; *load-truename*
@syindexanchor{*load-pathname*, SYM}
@syindexanchor{*load-truename*, SYM}
@subsection *load-pathname*, *load-truename* (Variable)
@cindex *load-pathname*
@cindex *load-truename*


@subsubheading Value Type:

@Thevalueof{*load-pathname*} must always be a @term{pathname}          or @nil{}.
@Thevalueof{*load-truename*} must always be a @term{physical pathname} or @nil{}.

@subsubheading Initial Value:

@nil{}.

@subsubheading Description:

During a call to @symbolref{load, SYM},
@symbolref{*load-pathname*, SYM} is @term{bound} to
the @term{pathname} denoted by the the first argument to @symbolref{load, SYM},
merged against the defaults;
that is, it is @term{bound} to @f{(pathname (merge-pathnames @param{filespec}))}.
During the same time interval,
@symbolref{*load-truename*, SYM} is @term{bound} to
the @term{truename} of the @term{file} being loaded.

At other times, the @term{value} of these @term{variables} is @nil{}.

If a @term{break loop} is entered while @symbolref{load, SYM} is ongoing,
it is @term{implementation-dependent} whether these @term{variables} retain
the @term{values} they had just prior to entering the @term{break loop}
or whether they are @term{bound} to @nil{}.

The consequences are unspecified if
an attempt is made to @term{assign} or @term{bind} either of these @term{variables}.

@subsubheading Affected By:

The @term{file system}.

@subsubheading See Also:

@ref{load}



@node *compile-print*; *compile-verbose*
@syindexanchor{*compile-print*, SYM}
@syindexanchor{*compile-verbose*, SYM}
@subsection *compile-print*, *compile-verbose* (Variable)
@cindex *compile-verbose*
@cindex *compile-print*



@subsubheading Value Type:

a @term{generalized boolean}.

@subsubheading Initial Value:

@term{implementation-dependent}.

@subsubheading Description:

@Thevalueof{*compile-print*}   is the default value of @thekeyarg{print}
to @symbolref{compile-file, SYM}.
@Thevalueof{*compile-verbose*} is the default value of @thekeyarg{verbose}
to @symbolref{compile-file, SYM}.

@subsubheading See Also:

@ref{compile-file}



@node *load-print*; *load-verbose*
@syindexanchor{*load-print*, SYM}
@syindexanchor{*load-verbose*, SYM}
@subsection *load-print*, *load-verbose* (Variable)
@cindex *load-verbose*
@cindex *load-print*
@anchor{*load-verbose*}


@subsubheading Value Type:

a @term{generalized boolean}.

@subsubheading Initial Value:

The initial @term{value} of @symbolref{*load-print*, SYM}   is @term{false}.
The initial @term{value} of @symbolref{*load-verbose*, SYM} is @term{implementation-dependent}.

@subsubheading Description:

@Thevalueof{*load-print*}   is the default value of @thekeyarg{print}   to @symbolref{load, SYM}.
@Thevalueof{*load-verbose*} is the default value of @thekeyarg{verbose} to @symbolref{load, SYM}.

@subsubheading See Also:

@ref{load}



@node *modules*
@syindexanchor{*modules*, SYM}
@subsection *modules* (Variable)
@cindex *modules*



@subsubheading Value Type:

a @term{list} of @term{strings}.

@subsubheading Initial Value:

@term{implementation-dependent}.

@subsubheading Description:

@Thevalueof{*modules*} is a list of names of the modules
that have been loaded into the current @term{Lisp image}.

@subsubheading Affected By:

@symbolref{provide, SYM}

@subsubheading See Also:

@ref{provide},
@ref{require}

@subsubheading Notes:

The variable @symbolref{*modules*, SYM} is deprecated.



@node provide; require
@syindexanchor{provide, SYM}
@syindexanchor{require, SYM}
@subsection provide, require (Function)
@cindex require
@cindex provide
@anchor{provide}
@anchor{require}



@subsubheading Syntax:

@DefunWithValues{provide, module-name, @term{implementation-dependent}}
@DefunWithValues{require, module-name @opt{} pathname-list, @term{implementation-dependent}}

@subsubheading Arguments and Values:

@param{module-name}---a @term{@symbolnamedesignator{}}.

@param{pathname-list}---@nil{}, or
a @term{designator}
for a @term{non-empty} @term{list} of @term{pathname designators}.
@Default{@nil{}}

@subsubheading Description:

@symbolref{provide, SYM} adds the @param{module-name} to the @term{list} held by
@symbolref{*modules*, SYM}, if such a name is not already present.

@symbolref{require, SYM} tests for the presence of the @param{module-name} in the
@term{list} held by @symbolref{*modules*, SYM}.
If it is present, @symbolref{require, SYM} immediately returns.
Otherwise, an attempt is made to load an appropriate set of @term{files} as follows:
The @param{pathname-list} argument, if @term{non-nil},
specifies a list of @term{pathnames} to be loaded in order, from left to right.
If the @param{pathname-list} is @nil{},
an @term{implementation-dependent} mechanism will be invoked in an attempt
to load the module named @param{module-name};
if no such module can be loaded, an error @oftype{error} is signaled.

Both functions use @symbolref{string=, SYM} to test for the presence of a @param{module-name}.

@subsubheading Examples:


@lisp
;;; This illustrates a nonportable use of REQUIRE, because it
;;; depends on the implementation-dependent file-loading mechanism.

(require "CALCULUS")

;;; This use of REQUIRE is nonportable because of the literal
;;; physical pathname.

(require "CALCULUS" "/usr/lib/lisp/calculus")

;;; One form of portable usage involves supplying a logical pathname,
;;; with appropriate translations defined elsewhere.

(require "CALCULUS" "lib:calculus")

;;; Another form of portable usage involves using a variable or
;;; table lookup function to determine the pathname, which again
;;; must be initialized elsewhere.

(require "CALCULUS" *calculus-module-pathname*)
@end lisp


@subsubheading Side Effects:

@symbolref{provide, SYM} modifies @symbolref{*modules*, SYM}.

@subsubheading Affected By:

The specific action taken by @symbolref{require, SYM} is affected by calls to @symbolref{provide, SYM}
(or, in general, any changes to @thevalueof{*modules*}).

@subsubheading Exceptional Situations:

@Shouldchecktype{module-name, a @term{@symbolnamedesignator{}}}

If @symbolref{require, SYM} fails to perform the requested operation
due to a problem while interacting with the @term{file system},
an error @oftype{file-error} is signaled.

An error @oftype{file-error} might be signaled if any @term{pathname}
in @param{pathname-list} is a @term{designator} for a @term{wild} @term{pathname}.

@subsubheading See Also:

@ref{*modules*},
@ref{Pathnames as Filenames}

@subsubheading Notes:

The functions @symbolref{provide, SYM} and @symbolref{require, SYM} are deprecated.

If a module consists of a single @term{package},
it is customary for the package and module names to be the same.