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<H1> 2. Universal SLIB Procedures </H1>
<!--docid::SEC13::-->
<P>

The procedures described in these sections are supported by all
implementations as part of the `<SAMP>*.init</SAMP>' files or by
`<TT>require.scm</TT>'.
</P>
<P>

<TABLE BORDER="0" CELLSPACING="0">
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_2.html#SEC14">2.1 Vicinity</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP">Pathname Management</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_2.html#SEC15">2.2 Configuration</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP">Characteristics of Scheme Implementation</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_2.html#SEC16">2.3 Input/Output</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP">Things not provided by the Scheme specs.</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_2.html#SEC17">2.4 System</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP">LOADing, EVALing, ERRORing, and EXITing</TD></TR>
<TR><TD ALIGN="left" VALIGN="TOP"><A HREF="slib_2.html#SEC18">2.5 Miscellany</A></TD><TD>&nbsp;&nbsp;</TD><TD ALIGN="left" VALIGN="TOP"></TD></TR>
</TABLE>
<P>

<A NAME="Vicinity"></A>
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<H2> 2.1 Vicinity </H2>
<!--docid::SEC14::-->
<P>

A vicinity is a descriptor for a place in the file system.  Vicinities
hide from the programmer the concepts of host, volume, directory, and
version.  Vicinities express only the concept of a file environment
where a file name can be resolved to a file in a system independent
manner.  Vicinities can even be used on <EM>flat</EM> file systems (which
have no directory structure) by having the vicinity express constraints
on the file name.  On most systems a vicinity would be a string.  All of
these procedures are file system dependent.
</P>
<P>

These procedures are provided by all implementations.
</P>
<P>

<A NAME="IDX56"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-vicinity</B> <I>dirpath</I>
<DD>Returns <VAR>dirpath</VAR> as a vicinity for use as first argument to
<CODE>in-vicinity</CODE>.
</DL>
<P>

<A NAME="IDX57"></A>
</P>
<DL>
<DT><U>Function:</U> <B>pathname-&gt;vicinity</B> <I>path</I>
<DD>Returns the vicinity containing <VAR>path</VAR>.
<TABLE><tr><td>&nbsp;</td><td class=example><pre>(pathname-&gt;vicinity &quot;/usr/local/lib/scm/Link.scm&quot;)
                    => &quot;/usr/local/lib/scm/&quot;
</pre></td></tr></table></DL>
<P>

<A NAME="IDX58"></A>
</P>
<DL>
<DT><U>Function:</U> <B>program-vicinity</B>
<DD>Returns the vicinity of the currently loading Scheme code.  For an
interpreter this would be the directory containing source code.  For a
compiled system (with multiple files) this would be the directory where
the object or executable files are.  If no file is currently loading it
the result is undefined.  <STRONG>Warning:</STRONG> <CODE>program-vicinity</CODE> can
return incorrect values if your program escapes back into a
<CODE>load</CODE>.
</DL>
<P>

<A NAME="IDX59"></A>
</P>
<DL>
<DT><U>Function:</U> <B>library-vicinity</B>
<DD>Returns the vicinity of the shared Scheme library.
</DL>
<P>

<A NAME="IDX60"></A>
</P>
<DL>
<DT><U>Function:</U> <B>implementation-vicinity</B>
<DD>Returns the vicinity of the underlying Scheme implementation.  This
vicinity will likely contain startup code and messages and a compiler.
</DL>
<P>

<A NAME="IDX61"></A>
</P>
<DL>
<DT><U>Function:</U> <B>user-vicinity</B>
<DD>Returns the vicinity of the current directory of the user.  On most
systems this is `<TT>&quot;&quot;</TT>' (the empty string).
</DL>
<P>

<A NAME="IDX62"></A>
</P>
<DL>
<DT><U>Function:</U> <B>home-vicinity</B>
<DD>Returns the vicinity of the user's <EM>HOME</EM> directory, the directory
<A NAME="IDX63"></A>
which typically contains files which customize a computer environment
for a user.  If scheme is running without a user (eg. a daemon) or if
this concept is meaningless for the platform, then <CODE>home-vicinity</CODE>
returns <CODE>#f</CODE>.
</DL>
<P>

<A NAME="IDX64"></A>
</P>
<DL>
<DT><U>Function:</U> <B>vicinity:suffix?</B> <I>chr</I>
<DD>Returns the `<SAMP>#t</SAMP>' if <VAR>chr</VAR> is a vicinity suffix character; and
<CODE>#f</CODE> otherwise.  Typical vicinity suffixes are `<SAMP>/</SAMP>',
`<SAMP>:</SAMP>', and `<SAMP>\</SAMP>',
</DL>
<P>

<A NAME="IDX65"></A>
</P>
<DL>
<DT><U>Function:</U> <B>in-vicinity</B> <I>vicinity filename</I>
<DD>Returns a filename suitable for use by <CODE>slib:load</CODE>,
<CODE>slib:load-source</CODE>, <CODE>slib:load-compiled</CODE>,
<CODE>open-input-file</CODE>, <CODE>open-output-file</CODE>, etc.  The returned
filename is <VAR>filename</VAR> in <VAR>vicinity</VAR>.  <CODE>in-vicinity</CODE> should
allow <VAR>filename</VAR> to override <VAR>vicinity</VAR> when <VAR>filename</VAR> is
an absolute pathname and <VAR>vicinity</VAR> is equal to the value of
<CODE>(user-vicinity)</CODE>.  The behavior of <CODE>in-vicinity</CODE> when
<VAR>filename</VAR> is absolute and <VAR>vicinity</VAR> is not equal to the value
of <CODE>(user-vicinity)</CODE> is unspecified.  For most systems
<CODE>in-vicinity</CODE> can be <CODE>string-append</CODE>.
</DL>
<P>

<A NAME="IDX66"></A>
</P>
<DL>
<DT><U>Function:</U> <B>sub-vicinity</B> <I>vicinity name</I>
<DD>Returns the vicinity of <VAR>vicinity</VAR> restricted to <VAR>name</VAR>.  This
is used for large systems where names of files in subsystems could
conflict.  On systems with directory structure <CODE>sub-vicinity</CODE> will
return a pathname of the subdirectory <VAR>name</VAR> of
<VAR>vicinity</VAR>.
</DL>
<P>

<A NAME="Configuration"></A>
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<H2> 2.2 Configuration </H2>
<!--docid::SEC15::-->
<P>

These constants and procedures describe characteristics of the Scheme
and underlying operating system.  They are provided by all
implementations.
</P>
<P>

<A NAME="IDX67"></A>
</P>
<DL>
<DT><U>Constant:</U> <B>char-code-limit</B>
<DD>An integer 1 larger that the largest value which can be returned by
<CODE>char-&gt;integer</CODE>.
</DL>
<P>

<A NAME="IDX68"></A>
</P>
<DL>
<DT><U>Constant:</U> <B>most-positive-fixnum</B>
<DD>In implementations which support integers of practically unlimited size,
<VAR>most-positive-fixnum</VAR> is a large exact integer within the range of
exact integers that may result from computing the length of a list,
vector, or string.
<P>

In implementations which do not support integers of practically
unlimited size, <VAR>most-positive-fixnum</VAR> is the largest exact integer
that may result from computing the length of a list, vector, or string.
</P>
</DL>
<P>

<A NAME="IDX69"></A>
</P>
<DL>
<DT><U>Constant:</U> <B>slib:tab</B>
<DD>The tab character.
</DL>
<P>

<A NAME="IDX70"></A>
</P>
<DL>
<DT><U>Constant:</U> <B>slib:form-feed</B>
<DD>The form-feed character.
</DL>
<P>

<A NAME="IDX71"></A>
</P>
<DL>
<DT><U>Function:</U> <B>software-type</B>
<DD>Returns a symbol denoting the generic operating system type.  For
instance, <CODE>unix</CODE>, <CODE>vms</CODE>, <CODE>macos</CODE>, <CODE>amiga</CODE>, or
<CODE>ms-dos</CODE>.
</DL>
<P>

<A NAME="IDX72"></A>
</P>
<DL>
<DT><U>Function:</U> <B>slib:report-version</B>
<DD>Displays the versions of SLIB and the underlying Scheme implementation
and the name of the operating system.  An unspecified value is returned.
<P>

<TABLE><tr><td>&nbsp;</td><td class=example><pre>(slib:report-version) => slib &quot;3a1&quot; on scm &quot;5b1&quot; on unix
</pre></td></tr></table></DL>
<P>

<A NAME="IDX73"></A>
</P>
<DL>
<DT><U>Function:</U> <B>slib:report</B>
<DD>Displays the information of <CODE>(slib:report-version)</CODE> followed by
almost all the information neccessary for submitting a problem report.
An unspecified value is returned.
<P>

<A NAME="IDX74"></A>
<DT><U>Function:</U> <B>slib:report</B> <I>#t</I>
<DD>provides a more verbose listing.
</P>
<P>

<A NAME="IDX75"></A>
<DT><U>Function:</U> <B>slib:report</B> <I>filename</I>
<DD>Writes the report to file `<TT>filename</TT>'.
</P>
<P>

<TABLE><tr><td>&nbsp;</td><td class=example><pre>(slib:report)
=>
slib &quot;3a1&quot; on scm &quot;5b1&quot; on unix
(implementation-vicinity) is &quot;/usr/local/lib/scm/&quot;
(library-vicinity) is &quot;/usr/local/lib/slib/&quot;
(scheme-file-suffix) is &quot;.scm&quot;
loaded *features* :
        trace alist qp sort
        common-list-functions macro values getopt
        compiled
implementation *features* :
        bignum complex real rational
        inexact vicinity ed getenv
        tmpnam abort transcript with-file
        ieee-p1178 r4rs rev4-optional-procedures hash
        object-hash delay eval dynamic-wind
        multiarg-apply multiarg/and- logical defmacro
        string-port source current-time record
        rev3-procedures rev2-procedures sun-dl string-case
        array dump char-ready? full-continuation
        system
implementation *catalog* :
        (i/o-extensions compiled &quot;/usr/local/lib/scm/ioext.so&quot;)
        ...
</pre></td></tr></table></DL>
<P>

<A NAME="Input/Output"></A>
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<H2> 2.3 Input/Output </H2>
<!--docid::SEC16::-->
<P>

These procedures are provided by all implementations.
</P>
<P>

<A NAME="IDX76"></A>
</P>
<DL>
<DT><U>Function:</U> <B>file-exists?</B> <I>filename</I>
<DD>Returns <CODE>#t</CODE> if the specified file exists.  Otherwise, returns
<CODE>#f</CODE>.  If the underlying implementation does not support this
feature then <CODE>#f</CODE> is always returned.
</DL>
<P>

<A NAME="IDX77"></A>
</P>
<DL>
<DT><U>Function:</U> <B>delete-file</B> <I>filename</I>
<DD>Deletes the file specified by <VAR>filename</VAR>.  If <VAR>filename</VAR> can not
be deleted, <CODE>#f</CODE> is returned.  Otherwise, <CODE>#t</CODE> is
returned.
</DL>
<P>

<A NAME="IDX78"></A>
</P>
<DL>
<DT><U>Function:</U> <B>open-file</B> <I>filename modes</I>
<DD><VAR>filename</VAR> should be a string naming a file.  <CODE>open-file</CODE>
returns a port depending on the symbol <VAR>modes</VAR>:
<P>

</P>
<DL COMPACT>
<DT>r
<DD>an input port capable of delivering characters from the file.
<DT>rb
<DD>a <EM>binary</EM> input port capable of delivering characters from the file.
<DT>w
<DD>an output port capable of writing characters to a new file by that name.
<DT>wb
<DD>a <EM>binary</EM> output port capable of writing characters to a new file
by that name.
</DL>
<P>

If an implementation does not distinguish between binary and non-binary
files, then it must treat rb as r and wb as w.
</P>
<P>

If the file cannot be opened, either #f is returned or an error is
signalled.  For output, if a file with the given name already exists,
the effect is unspecified.
</P>
</DL>
<P>

<A NAME="IDX79"></A>
</P>
<DL>
<DT><U>Function:</U> <B>port?</B> <I>obj</I>
<DD>Returns <TT>#t</TT> if <VAR>obj</VAR> is an input or output port, otherwise
returns <TT>#f</TT>.
</DL>
<P>

<A NAME="IDX80"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>close-port</B> <I>port</I>
<DD>Closes the file associated with <VAR>port</VAR>, rendering the <VAR>port</VAR>
incapable of delivering or accepting characters.
<P>

<CODE>close-file</CODE> has no effect if the file has already been closed.
The value returned is unspecified.
</P>
</DL>
<P>

<A NAME="IDX81"></A>
</P>
<DL>
<DT><U>Function:</U> <B>call-with-open-ports</B> <I>proc ports <small>...</small></I>
<DD><A NAME="IDX82"></A>
<DT><U>Function:</U> <B>call-with-open-ports</B> <I>ports <small>...</small> proc</I>
<DD><VAR>Proc</VAR> should be a procedure that accepts as many arguments as there
are <VAR>ports</VAR> passed to <CODE>call-with-open-ports</CODE>.
<CODE>call-with-open-ports</CODE> calls <VAR>proc</VAR> with <VAR>ports</VAR> <small>...</small>.
If <VAR>proc</VAR> returns, then the ports are closed automatically and the
value yielded by the <VAR>proc</VAR> is returned.  If <VAR>proc</VAR> does not
return, then the ports will not be closed automatically unless it is
possible to prove that the ports will never again be used for a read or
write operation.
</DL>
<P>

<A NAME="IDX83"></A>
</P>
<DL>
<DT><U>Function:</U> <B>tmpnam</B>
<DD>Returns a pathname for a file which will likely not be used by any other
process.  Successive calls to <CODE>(tmpnam)</CODE> will return different
pathnames.
</DL>
<P>

<A NAME="IDX84"></A>
</P>
<DL>
<DT><U>Function:</U> <B>current-error-port</B>
<DD>Returns the current port to which diagnostic and error output is
directed.
</DL>
<P>

<A NAME="IDX85"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>force-output</B>
<DD><A NAME="IDX86"></A>
<DT><U>Procedure:</U> <B>force-output</B> <I>port</I>
<DD>Forces any pending output on <VAR>port</VAR> to be delivered to the output
device and returns an unspecified value.  The <VAR>port</VAR> argument may be
omitted, in which case it defaults to the value returned by
<CODE>(current-output-port)</CODE>.
</DL>
<P>

<A NAME="IDX87"></A>
</P>
<DL>
<DT><U>Function:</U> <B>output-port-width</B>
<DD><A NAME="IDX88"></A>
<DT><U>Function:</U> <B>output-port-width</B> <I>port</I>
<DD><P>

Returns the width of <VAR>port</VAR>, which defaults to
<CODE>(current-output-port)</CODE> if absent.  If the width cannot be
determined 79 is returned.
</P>
</DL>
<P>

<A NAME="IDX89"></A>
</P>
<DL>
<DT><U>Function:</U> <B>output-port-height</B>
<DD><A NAME="IDX90"></A>
<DT><U>Function:</U> <B>output-port-height</B> <I>port</I>
<DD><P>

Returns the height of <VAR>port</VAR>, which defaults to
<CODE>(current-output-port)</CODE> if absent.  If the height cannot be
determined 24 is returned.
</P>
</DL>
<P>

<A NAME="System"></A>
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<H2> 2.4 System </H2>
<!--docid::SEC17::-->
<P>

These procedures are provided by all implementations.
</P>
<P>

<A NAME="IDX91"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>slib:load-source</B> <I>name</I>
<DD>Loads a file of Scheme source code from <VAR>name</VAR> with the default
filename extension used in SLIB.  For instance if the filename extension
used in SLIB is `<TT>.scm</TT>' then <CODE>(slib:load-source &quot;foo&quot;)</CODE> will
load from file `<TT>foo.scm</TT>'.
</DL>
<P>

<A NAME="IDX92"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>slib:load-compiled</B> <I>name</I>
<DD>On implementations which support separtely loadable compiled modules,
loads a file of compiled code from <VAR>name</VAR> with the implementation's
filename extension for compiled code appended.
</DL>
<P>

<A NAME="IDX93"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>slib:load</B> <I>name</I>
<DD>Loads a file of Scheme source or compiled code from <VAR>name</VAR> with the
appropriate suffixes appended.  If both source and compiled code are
present with the appropriate names then the implementation will load
just one.  It is up to the implementation to choose which one will be
loaded.
<P>

If an implementation does not support compiled code then
<CODE>slib:load</CODE> will be identical to <CODE>slib:load-source</CODE>.
</P>
</DL>
<P>

<A NAME="IDX94"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>slib:eval</B> <I>obj</I>
<DD><CODE>eval</CODE> returns the value of <VAR>obj</VAR> evaluated in the current top
level environment.  <A HREF="slib_7.html#SEC246">7.4.11 Eval</A> provides a more general evaluation
facility.
</DL>
<P>

<A NAME="IDX95"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>slib:eval-load</B> <I>filename eval</I>
<DD><VAR>filename</VAR> should be a string.  If filename names an existing file,
the Scheme source code expressions and definitions are read from the
file and <VAR>eval</VAR> called with them sequentially.  The
<CODE>slib:eval-load</CODE> procedure does not affect the values returned by
<CODE>current-input-port</CODE> and <CODE>current-output-port</CODE>.
</DL>
<P>

<A NAME="IDX96"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>slib:warn</B> <I>arg1 arg2 <small>...</small></I>
<DD>Outputs a warning message containing the arguments.
</DL>
<P>

<A NAME="IDX97"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>slib:error</B> <I>arg1 arg2 <small>...</small></I>
<DD>Outputs an error message containing the arguments, aborts evaluation of
the current form and responds in a system dependent way to the error.
Typical responses are to abort the program or to enter a read-eval-print
loop.
</DL>
<P>

<A NAME="IDX98"></A>
</P>
<DL>
<DT><U>Procedure:</U> <B>slib:exit</B> <I>n</I>
<DD><A NAME="IDX99"></A>
<DT><U>Procedure:</U> <B>slib:exit</B>
<DD>Exits from the Scheme session returning status <VAR>n</VAR> to the system.
If <VAR>n</VAR> is omitted or <CODE>#t</CODE>, a success status is returned to the
system (if possible).  If <VAR>n</VAR> is <CODE>#f</CODE> a failure is returned to
the system (if possible).  If <VAR>n</VAR> is an integer, then <VAR>n</VAR> is
returned to the system (if possible).  If the Scheme session cannot exit
an unspecified value is returned from <CODE>slib:exit</CODE>.
</DL>
<P>

<A NAME="IDX100"></A>
</P>
<DL>
<DT><U>Function:</U> <B>browse-url</B> <I>url</I>
<DD>Web browsers have become so ubiquitous that programming languagues
should support a uniform interface to them.
<P>

If a `<SAMP>netscape</SAMP>' browser is running, <CODE>browse-url</CODE> causes the
browser to display the page specified by string <VAR>url</VAR> and returns
#t.
</P>
<P>

If the browser is not running, <CODE>browse-url</CODE> starts a browser
displaying the argument <VAR>url</VAR>.  If the browser starts as a
background job, <CODE>browse-url</CODE> returns #t immediately; if the
browser starts as a foreground job, then <CODE>browse-url</CODE> returns #t
when the browser exits; otherwise it returns #f.
</P>
</DL>
<P>

<A NAME="Miscellany"></A>
<HR SIZE="6">
<A NAME="SEC18"></A>
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<TD VALIGN="MIDDLE" ALIGN="LEFT">[<A HREF="slib_abt.html#SEC_About"> ? </A>]</TD>
</TR></TABLE>
<H2> 2.5 Miscellany </H2>
<!--docid::SEC18::-->
<P>

These procedures are provided by all implementations.
</P>
<P>

<A NAME="IDX101"></A>
</P>
<DL>
<DT><U>Function:</U> <B>identity</B> <I>x</I>
<DD><VAR>identity</VAR> returns its argument.
<P>

Example:
<TABLE><tr><td>&nbsp;</td><td class=example><pre>(identity 3)
   => 3
(identity '(foo bar))
   => (foo bar)
(map identity <VAR>lst</VAR>)
   == (copy-list <VAR>lst</VAR>)
</pre></td></tr></table></DL>
<P>

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</TR></TABLE>
<H3> 2.5.1 Mutual Exclusion </H3>
<!--docid::SEC19::-->
<P>

An <EM>exchanger</EM> is a procedure of one argument regulating mutually
<A NAME="IDX102"></A>
exclusive access to a resource.  When a exchanger is called, its current
content is returned, while being replaced by its argument in an atomic
operation.
</P>
<P>

<A NAME="IDX103"></A>
</P>
<DL>
<DT><U>Function:</U> <B>make-exchanger</B> <I>obj</I>
<DD><P>

Returns a new exchanger with the argument <VAR>obj</VAR> as its initial
content.
</P>
<P>

<TABLE><tr><td>&nbsp;</td><td class=example><pre>(define queue (make-exchanger (list a)))
</pre></td></tr></table><P>

A queue implemented as an exchanger holding a list can be protected from
reentrant execution thus:
</P>
<P>

<TABLE><tr><td>&nbsp;</td><td class=example><pre>(define (pop queue)
  (let ((lst #f))
    (dynamic-wind
        (lambda () (set! lst (queue #f)))
        (lambda () (and lst (not (null? lst))
                        (let ((ret (car lst)))
                          (set! lst (cdr lst))
                          ret)))
        (lambda () (and lst (queue lst))))))

(pop queue)         => a

(pop queue)         => #f
</pre></td></tr></table></DL>
<P>

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</TR></TABLE>
<H3> 2.5.2 Legacy </H3>
<!--docid::SEC20::-->
<P>

The following procedures were present in Scheme until R4RS
(see section `Language changes' in <CITE>Revised(4) Scheme</CITE>).
They are provided by all SLIB implementations.
</P>
<P>

<A NAME="IDX104"></A>
</P>
<DL>
<DT><U>Constant:</U> <B>t</B>
<DD>Derfined as <CODE>#t</CODE>.
</DL>
<P>

<A NAME="IDX105"></A>
</P>
<DL>
<DT><U>Constant:</U> <B>nil</B>
<DD>Defined as <CODE>#f</CODE>.
</DL>
<P>

<A NAME="IDX106"></A>
</P>
<DL>
<DT><U>Function:</U> <B>last-pair</B> <I>l</I>
<DD>Returns the last pair in the list <VAR>l</VAR>.  Example:
<TABLE><tr><td>&nbsp;</td><td class=example><pre>(last-pair (cons 1 2))
   => (1 . 2)
(last-pair '(1 2))
   => (2)
    == (cons 2 '())
</pre></td></tr></table></DL>
<P>

<A NAME="Scheme Syntax Extension Packages"></A>
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