<HTML> <HEAD> <!-- Created by texi2html 1.56k + clip patches and <A href="http://www.clip.dia.fi.upm.es/Software">lpdoc</A> from ciao.texi on 28 January 2007 --> <LINK rel="stylesheet" href="ciao.css" type="text/css"> <TITLE>The Ciao Prolog System - Changing system behaviour and various flags</TITLE> </HEAD> <BODY> Go to the <A HREF="ciao_1.html">first</A>, <A HREF="ciao_26.html">previous</A>, <A HREF="ciao_28.html">next</A>, <A HREF="ciao_241.html">last</A> section, <A HREF="ciao_toc.html">table of contents</A>. <P><HR><P> <H1><A NAME="SEC163" HREF="ciao_toc.html#TOC163">Changing system behaviour and various flags</A></H1> <P> <A NAME="IDX1851"></A> <P> <STRONG>Author(s):</STRONG> Daniel Cabeza, Mats Carlsson. <P> <STRONG>Version:</STRONG> 1.10#7 (2006/4/26, 19:22:13 CEST) <P> <STRONG>Version of last change:</STRONG> 1.7#213 (2002/5/14, 18:11:29 CEST) <P> <A NAME="IDX1852"></A> <A NAME="IDX1853"></A> Flags define some parameters of the system and control the behavior of system or library predicates. Each flag has a name and an associated predefined value, and except some system flags which are fixed in general their associated value is changeable. Predefined flags in the system are: <DL COMPACT> <DT><CODE>version</CODE> <DD> The Ciao version, as a term <CODE>ciao</CODE>(<CODE>Version</CODE>,<CODE>Patch</CODE>). <CODE>Version</CODE> is a floating point number, <CODE>Patch</CODE> is an integer. Unchangeable. <DT><CODE>argv</CODE> <DD> Its value is a list of atoms representing the program arguments supplied when the current executable was invoked. This is the value to which is instantiated the argument of the <A NAME="IDX1854"></A> <CODE>main/1</CODE> predicate at executable startup. Unchangeable. <DT><CODE>bounded</CODE> <DD> It is <CODE>false</CODE>, to denote that the range of integers can be considered infinite (but see <A NAME="IDX1855"></A> <CODE>int/1</CODE>). Unchangeable. <KBD> * ISO * </KBD> <DT><CODE>fileerrors</CODE> <DD> If <CODE>on</CODE>, predicates handling files give errors (throw exceptions) when a file is inexistent or an operation is not allowed. If <CODE>off</CODE>, fail in that conditions. Initially <CODE>on</CODE>. <DT><CODE>gc</CODE> <DD> Controls whether garbage collection is done. May be <CODE>on</CODE> (default) or <CODE>off</CODE>. <DT><CODE>gc_margin</CODE> <DD> An integer <CODE>Margin</CODE>. If less than <CODE>Margin</CODE> kilobytes are reclaimed in a garbage collection then the size of the garbage collected area should be increased. Also, no garbage collection is attempted unless the garbage collected area has at least <CODE>Margin</CODE> kilobytes. Initially 500. <DT><CODE>gc_trace</CODE> <DD> Governs garbage collection trace messages. An element off <CODE>[on,off,terse,verbose]</CODE>. Initially <CODE>off</CODE>. <DT><CODE>integer_rounding_function</CODE> <DD> It is <CODE>toward_zero</CODE>, so that <CODE>-1 =:= -3//2</CODE> succeeds. Unchangeable. <KBD> * ISO * </KBD> <DT><CODE>max_arity</CODE> <DD> It is 255, so that no compound term (or predicate) can have more than this number of arguments. Unchangeable. <KBD> * ISO * </KBD> <DT><CODE>quiet</CODE> <DD> Controls which messages issued using <A NAME="IDX1856"></A> <CODE>io_aux</CODE> are actually written. As the system uses that library to report its messages, this flag controls the <EM>verbosity</EM> of the system. Possible states of the flag are: <DL COMPACT> <DT><CODE>on</CODE> <DD> No messages are reported. <DT><CODE>error</CODE> <DD> Only error messages are reported. <DT><CODE>warning</CODE> <DD> Only error and warning messages are reported. <DT><CODE>off</CODE> <DD> All messages are reported, except debug messages. This is the default state. <DT><CODE>debug</CODE> <DD> All messages, including debug messages, are reported. This is only intended for the system implementators. </DL> <DT><CODE>unknown</CODE> <DD> Controls action on calls to undefined predicates. The possible states of the flag are: <DL COMPACT> <DT><CODE>error</CODE> <DD> An error is thrown with the <A NAME="IDX1857"></A> error term <CODE>existence_error(procedure, F/A)</CODE>. <DT><CODE>fail</CODE> <DD> The call simply fails. <DT><CODE>warning</CODE> <DD> A warning is written and the call fails. </DL> The state is initially <CODE>error</CODE>. <KBD> * ISO * </KBD> </DL> <UL> <LI><A HREF="ciao_27.html#SEC164">Usage and interface (prolog_flags)</A> <LI><A HREF="ciao_27.html#SEC165">Documentation on exports (prolog_flags)</A> <LI><A HREF="ciao_27.html#SEC166">Documentation on multifiles (prolog_flags)</A> </UL> <H2><A NAME="SEC164" HREF="ciao_toc.html#TOC164">Usage and interface (<CODE>prolog_flags</CODE>)</A></H2> <div class="cartouche"> <UL> <LI><STRONG>Library usage:</STRONG> These predicates are builtin in Ciao, so nothing special has to be done to use them. <LI><STRONG>Exports:</STRONG> <UL> <LI><EM>Predicates:</EM> <A NAME="IDX1858"></A> <CODE>set_prolog_flag/2</CODE>, <A NAME="IDX1859"></A> <CODE>current_prolog_flag/2</CODE>, <A NAME="IDX1860"></A> <CODE>prolog_flag/3</CODE>, <A NAME="IDX1861"></A> <CODE>push_prolog_flag/2</CODE>, <A NAME="IDX1862"></A> <CODE>pop_prolog_flag/1</CODE>, <A NAME="IDX1863"></A> <CODE>prompt/2</CODE>, <A NAME="IDX1864"></A> <CODE>gc/0</CODE>, <A NAME="IDX1865"></A> <CODE>nogc/0</CODE>, <A NAME="IDX1866"></A> <CODE>fileerrors/0</CODE>, <A NAME="IDX1867"></A> <CODE>nofileerrors/0</CODE>. <LI><EM>Multifiles:</EM> <A NAME="IDX1868"></A> <CODE>define_flag/3</CODE>. </UL> </UL> </div class="cartouche"> <H2><A NAME="SEC165" HREF="ciao_toc.html#TOC165">Documentation on exports (<CODE>prolog_flags</CODE>)</A></H2> <P> <A NAME="IDX1869"></A> <A NAME="IDX1870"></A> <DL> <DT><span class="define">PREDICATE:</span> <B>set_prolog_flag/2:</B> <DD><A NAME="IDX1871"></A> <P> <CODE>set_prolog_flag(FlagName, Value)</CODE> <P> Set existing flag <CODE>FlagName</CODE> to <CODE>Value</CODE>. </DL> <P> <A NAME="IDX1872"></A> <A NAME="IDX1873"></A> <DL> <DT><span class="define">PREDICATE:</span> <B>current_prolog_flag/2:</B> <DD><A NAME="IDX1874"></A> <P> <CODE>current_prolog_flag(FlagName, Value)</CODE> <P> <CODE>FlagName</CODE> is an existing flag and <CODE>Value</CODE> is the value currently associated with it. </DL> <P> <A NAME="IDX1875"></A> <A NAME="IDX1876"></A> <DL> <DT><span class="define">PREDICATE:</span> <B>prolog_flag/3:</B> <DD><A NAME="IDX1877"></A> <P> <CODE>prolog_flag(FlagName, OldValue, NewValue)</CODE> <P> <CODE>FlagName</CODE> is an existing flag, unify <CODE>OldValue</CODE> with the value associated with it, and set it to new value <CODE>NewValue</CODE>. <P> <STRONG>Usage 1:</STRONG> <CODE>prolog_flag(?atm, ?term, +term)</CODE> <UL> <LI><EM>The following properties hold globally:</EM> This predicate is understood natively by CiaoPP. (<CODE>basic_props:native/1</CODE>) </UL> <P> <STRONG>Usage 2:</STRONG> <CODE>prolog_flag(?FlagName, -OldValue, -NewValue)</CODE> <UL> <LI><EM>Description:</EM> Same as <CODE>current_prolog_flag(<CODE>FlagName</CODE>, <CODE>OldValue</CODE>)</CODE> <LI><EM>The following properties should hold at call time:</EM> <CODE>FlagName</CODE> is an atom. (<CODE>basic_props:atm/1</CODE>) The terms <CODE>OldValue</CODE> and <CODE>NewValue</CODE> are strictly identical. (<CODE>term_compare:== /2</CODE>) <LI><EM>The following properties hold globally:</EM> This predicate is understood natively by CiaoPP. (<CODE>basic_props:native/1</CODE>) </UL> </DL> <P> <A NAME="IDX1878"></A> <A NAME="IDX1879"></A> <DL> <DT><span class="define">PREDICATE:</span> <B>push_prolog_flag/2:</B> <DD><A NAME="IDX1880"></A> <P> <CODE>push_prolog_flag(Flag, NewValue)</CODE> <P> Same as <A NAME="IDX1881"></A> <CODE>set_prolog_flag/2</CODE>, but storing current value of <CODE>Flag</CODE> to restore it with <A NAME="IDX1882"></A> <CODE>pop_prolog_flag/1</CODE>. </DL> <P> <A NAME="IDX1883"></A> <A NAME="IDX1884"></A> <DL> <DT><span class="define">PREDICATE:</span> <B>pop_prolog_flag/1:</B> <DD><A NAME="IDX1885"></A> <P> <CODE>pop_prolog_flag(Flag)</CODE> <P> Restore the value of <CODE>Flag</CODE> previous to the last non-canceled <A NAME="IDX1886"></A> <CODE>push_prolog_flag/2</CODE> on it. </DL> <P> <A NAME="IDX1887"></A> <A NAME="IDX1888"></A> <DL> <DT><span class="define">PREDICATE:</span> <B>prompt/2:</B> <DD><A NAME="IDX1889"></A> <P> <CODE>prompt(Old, New)</CODE> <P> Unify <CODE>Old</CODE> with the current prompt for reading, change it to <CODE>New</CODE>. <P> <STRONG>Usage 2:</STRONG> <CODE>prompt(Old, New)</CODE> <UL> <LI><EM>Description:</EM> Unify <CODE>Old</CODE> with the current prompt for reading without changing it. <LI><EM>The following properties should hold at call time:</EM> <CODE>Old</CODE> is a free variable. (<CODE>term_typing:var/1</CODE>) <CODE>New</CODE> is a free variable. (<CODE>term_typing:var/1</CODE>) The terms <CODE>Old</CODE> and <CODE>New</CODE> are strictly identical. (<CODE>term_compare:== /2</CODE>) <LI><EM>The following properties hold upon exit:</EM> <CODE>Old</CODE> is an atom. (<CODE>basic_props:atm/1</CODE>) <CODE>New</CODE> is an atom. (<CODE>basic_props:atm/1</CODE>) </UL> </DL> <P> <A NAME="IDX1890"></A> <A NAME="IDX1891"></A> <DL> <DT><span class="define">PREDICATE:</span> <B>gc/0:</B> <DD><A NAME="IDX1892"></A> <P> <STRONG>Usage:</STRONG> <UL> <LI><EM>Description:</EM> Enable garbage collection. Equivalent to <CODE>set_prolog_flag(gc, on)</CODE> </UL> </DL> <P> <A NAME="IDX1893"></A> <A NAME="IDX1894"></A> <DL> <DT><span class="define">PREDICATE:</span> <B>nogc/0:</B> <DD><A NAME="IDX1895"></A> <P> <STRONG>Usage:</STRONG> <UL> <LI><EM>Description:</EM> Disable garbage collection. Equivalent to <CODE>set_prolog_flag(gc, off)</CODE> </UL> </DL> <P> <A NAME="IDX1896"></A> <A NAME="IDX1897"></A> <DL> <DT><span class="define">PREDICATE:</span> <B>fileerrors/0:</B> <DD><A NAME="IDX1898"></A> <P> <STRONG>Usage:</STRONG> <UL> <LI><EM>Description:</EM> Enable reporting of file errors. Equivalent to <CODE>set_prolog_flag(fileerrors, on)</CODE> </UL> </DL> <P> <A NAME="IDX1899"></A> <A NAME="IDX1900"></A> <DL> <DT><span class="define">PREDICATE:</span> <B>nofileerrors/0:</B> <DD><A NAME="IDX1901"></A> <P> <STRONG>Usage:</STRONG> <UL> <LI><EM>Description:</EM> Disable reporting of file errors. Equivalent to <CODE>set_prolog_flag(fileerrors, off)</CODE> </UL> </DL> <H2><A NAME="SEC166" HREF="ciao_toc.html#TOC166">Documentation on multifiles (<CODE>prolog_flags</CODE>)</A></H2> <P> <A NAME="IDX1902"></A> <A NAME="IDX1903"></A> <DL> <DT><span class="define">PREDICATE:</span> <B>define_flag/3:</B> <DD><A NAME="IDX1904"></A> <P> <CODE>define_flag(Flag, Values, Default)</CODE> <P> New flags can be defined by writing facts of this predicate. <CODE>Flag</CODE> is the name of the new flag, <CODE>Values</CODE> defines the posible values for the flag (see below) and <CODE>Default</CODE> defines the predefined value associated with the flag (which should be compatible with <CODE>Values</CODE>). <P> The predicate is <EM>multifile</EM>. <P> <STRONG>Usage 1:</STRONG> <CODE>define_flag(-atm, Values, -atm)</CODE> <UL> <LI><EM>Description:</EM> Posible values for the flag are atoms. Example: <PRE> :- multifile define_flag/3. define_flag(tmpdir, atom, '/tmp'). </PRE> <LI><EM>Call and exit should be <EM>compatible</EM> with:</EM> The terms <CODE>Values</CODE> and <CODE>atom</CODE> are strictly identical. (<CODE>term_compare:== /2</CODE>) </UL> <P> <STRONG>Usage 2:</STRONG> <CODE>define_flag(-atm, Values, -int)</CODE> <UL> <LI><EM>Description:</EM> Posible values for the flag are integers. Example: <PRE> :- multifile define_flag/3. define_flag(max_connections, integer, 10). </PRE> <LI><EM>Call and exit should be <EM>compatible</EM> with:</EM> The terms <CODE>Values</CODE> and <CODE>integer</CODE> are strictly identical. (<CODE>term_compare:== /2</CODE>) </UL> <P> <STRONG>Usage 3:</STRONG> <CODE>define_flag(Flag, Values, Default)</CODE> <UL> <LI><EM>Description:</EM> Posible values for the flag are the elements of <CODE>Values</CODE>. Example: <PRE> :- multifile define_flag/3. define_flag(debug, [on,debug,trace,off], off). </PRE> <LI><EM>Call and exit should be <EM>compatible</EM> with:</EM> <CODE>Flag</CODE> is an atom. (<CODE>basic_props:atm/1</CODE>) <CODE>Values</CODE> is a list. (<CODE>basic_props:list/1</CODE>) <LI><EM>The following properties should hold upon exit:</EM> <CODE>Default</CODE> is an element of <CODE>Values</CODE>. (<CODE>basic_props:member/2</CODE>) </UL> </DL> <P><HR><P> Go to the <A HREF="ciao_1.html">first</A>, <A HREF="ciao_26.html">previous</A>, <A HREF="ciao_28.html">next</A>, <A HREF="ciao_241.html">last</A> section, <A HREF="ciao_toc.html">table of contents</A>. </BODY> </HTML>
