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<H3 CLASS="subsection"><A NAME="htoc150">7.14</A>&#XA0;&#XA0;Term input/output</H3><UL>
<LI><A HREF="gprolog037.html#toc115"><TT>read_term/3</TT>,
<TT>read_term/2</TT>,
<TT>read/2</TT>,
<TT>read/1</TT></A>
</LI><LI><A HREF="gprolog037.html#toc116"><TT>read_atom/2</TT>,
<TT>read_atom/1</TT>, 
<TT>read_integer/2</TT>,
<TT>read_integer/1</TT>,<BR>
 <TT>read_number/2</TT>,
<TT>read_number/1</TT></A>
</LI><LI><A HREF="gprolog037.html#toc117"><TT>read_token/2</TT>,
<TT>read_token/1</TT></A>
</LI><LI><A HREF="gprolog037.html#toc118"><TT>syntax_error_info/4</TT></A>
</LI><LI><A HREF="gprolog037.html#toc119"><TT>last_read_start_line_column/2</TT></A>
</LI><LI><A HREF="gprolog037.html#toc120"><TT>write_term/3</TT>,
<TT>write_term/2</TT>,
<TT>write/2</TT>,
<TT>write/1</TT>,
<TT>writeq/2</TT>,
<TT>writeq/1</TT>,<BR>
 <TT>write_canonical/2</TT>,
<TT>write_canonical/1</TT>,
<TT>display/2</TT>,
<TT>display/1</TT>,
<TT>print/2</TT>,<BR>
 <TT>print/1</TT></A>
</LI><LI><A HREF="gprolog037.html#toc121"><TT>format/3</TT>,
<TT>format/2</TT></A>
</LI><LI><A HREF="gprolog037.html#toc122"><TT>portray_clause/2</TT>,
<TT>portray_clause/1</TT></A>
</LI><LI><A HREF="gprolog037.html#toc123"><TT>get_print_stream/1</TT></A>
</LI><LI><A HREF="gprolog037.html#toc124"><TT>op/3</TT></A>
</LI><LI><A HREF="gprolog037.html#toc125"><TT>current_op/3</TT></A>
</LI><LI><A HREF="gprolog037.html#toc126"><TT>char_conversion/2</TT></A>
</LI><LI><A HREF="gprolog037.html#toc127"><TT>current_char_conversion/2</TT></A>
</LI></UL>
<P>
<A NAME="Term-input/output"></A>
These built-in predicates enable a Prolog term to be input from or output to
a text stream. The atom <TT>end_of_file</TT> is returned as term to
indicate the end-of-file. The syntax of such terms can also be altered by
changing the operators (section&#XA0;<A HREF="#op/3:(Term-input/output)">7.14.10</A>), and making some
characters equivalent to others (section&#XA0;<A HREF="#char-conversion/2">7.14.12</A>) if the
<TT>char_conversion</TT> Prolog flag is <TT>on</TT>
(section&#XA0;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>). Double quoted tokens will be returned as an atom
or a character list or a character code list depending on the value of the
<TT>double_quotes</TT> Prolog flag (section&#XA0;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>). Similarly, back quoted tokens are returned depending on the value of the
<TT>back_quotes</TT> Prolog flag.</P><H4 CLASS="subsubsection"><A NAME="toc115"></A><A NAME="htoc151">7.14.1</A>&#XA0;&#XA0;<TT>read_term/3</TT>,
<TT>read_term/2</TT>,
<TT>read/2</TT>,
<TT>read/1</TT></H4><P>
<A NAME="read-term/3"></A>



</P><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
</DT><DD CLASS="dd-list"><TT>
read_term(+stream_or_alias, ?term, +read_option_list)<BR>
read_term(?term, +read_option_list)<BR>
read(+stream_or_alias, ?term)<BR>
read(?term)</TT></DD></DL><P><B>Description</B></P><P><TT>read_term(SorA, Term, Options)</TT> is true if
<TT>Term</TT> unifies with the next term read from the stream associated
with the stream-term or alias <TT>SorA</TT> according to the options given by
<TT>Options</TT>.</P><P><B>Read options</B>: <TT>Options</TT> is a list of read options. If this
list contains contradictory options, the rightmost option is the one which
applies. Possible options are:</P><UL CLASS="itemize"><LI CLASS="li-itemize"><TT>variables(VL)</TT>: <TT>VL</TT> is unified with the
list of all variables of the input term, in left-to-right traversal
order. Anonymous variables are included in the list <TT>VL</TT>.</LI><LI CLASS="li-itemize"><TT>variable_names(VNL)</TT>: <TT>VNL</TT> is
unified with the list of pairs <TT>Name = Var</TT> where <TT>Var</TT> is a
named variable of the term and <TT>Name</TT> is the atom associated with the
name of <TT>Var</TT>. Anonymous variables are not included in the list
<TT>VNL</TT>.</LI><LI CLASS="li-itemize"><TT>singletons(SL)</TT>: <TT>SL</TT> is unified with the
list of pairs <TT>Name = Var</TT> where <TT>Var</TT> is a named variable
which occurs only once in the term and <TT>Name</TT> is the atom associated
to the name of <TT>Var</TT>. Anonymous variables are not included in the list
<TT>SL</TT>.</LI><LI CLASS="li-itemize"><TT>syntax_error(error</TT>/<TT>warning</TT>/<TT>fail)</TT>:
specifies the effect of a syntax error:<UL CLASS="itemize"><LI CLASS="li-itemize"><TT>error</TT>: a <TT>syntax_error</TT> is raised.</LI><LI CLASS="li-itemize"><TT>warning</TT>: a warning message is displayed and the predicate
fails.</LI><LI CLASS="li-itemize"><TT>fail</TT>: the predicate quietly fails.</LI></UL><P>The default value is the value of the <TT>syntax_error</TT>
Prolog flag (section&#XA0;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>).</P></LI><LI CLASS="li-itemize"><TT>end_of_term(dot</TT>/<TT>eof)</TT>: specifies the
end-of-term delimiter: <TT>dot</TT> is the classical full-stop delimiter (a
dot followed with a layout character), <TT>eof</TT> is the end-of-file
delimiter. This option is useful for predicates like
<TT>read_term_from_atom/3</TT> (section&#XA0;<A HREF="gprolog038.html#read-term-from-atom/3">7.15.1</A>) to avoid to add a
terminal dot at the end of the atom. The default value is <TT>dot</TT>.</LI></UL><P><TT>read(SorA, Term)</TT> is equivalent to
<TT>read_term(SorA, Term, [])</TT>.</P><P><TT>read_term/2</TT> and <TT>read/1</TT> apply to the current input stream.</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Options</TT> is a partial list or a list with an element
<TT>E</TT> which is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is neither a variable nor a stream-term or alias</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(stream_or_alias, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Options</TT> is neither a partial list nor a list</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(list, Options)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
an element <TT>E</TT> of the <TT>Options</TT> list is neither a
variable nor a valid read option</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(read_option, E)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is not associated with an open stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>existence_error(stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is an output stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(input, stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is associated with a binary stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(input, binary_stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> has stream properties <TT>end_of_stream(past)</TT>
and <TT>eof_action(error)</TT></TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(input, past_end_of_stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
a syntax error occurs and the value of the <TT>syntax_error</TT>
Prolog flag is <TT>error</TT> (section&#XA0;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>syntax_error(<I>atom explaining the error</I>)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
</TABLE><P><B>Portability</B></P><P>ISO predicates. The ISO reference raises a
<TT>representation_error(Flag)</TT> where <TT>Flag</TT> is
<TT>max_arity</TT>,<TT> max_integer</TT>, or<TT> min_integer</TT> when
the read term breaches an implementation defined limit specified by
<TT>Flag</TT>. GNU Prolog detects neither <TT>min_integer</TT> nor
<TT>max_integer</TT> violation and treats a <TT>max_arity</TT> violation
as a syntax error. The read options <TT>syntax_error/1</TT> and
<TT>end_of_term/1</TT> are GNU Prolog extensions.</P><H4 CLASS="subsubsection"><A NAME="toc116"></A><A NAME="htoc152">7.14.2</A>&#XA0;&#XA0;<TT>read_atom/2</TT>,
<TT>read_atom/1</TT>, 
<TT>read_integer/2</TT>,
<TT>read_integer/1</TT>,<BR>
 <TT>read_number/2</TT>,
<TT>read_number/1</TT></H4><P>
<A NAME="read-atom/2"></A>





</P><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
</DT><DD CLASS="dd-list"><TT>
read_atom(+stream_or_alias, ?atom)<BR>
read_atom(?atom)<BR>
read_integer(+stream_or_alias, ?integer)<BR>
read_integer(?integer)<BR>
read_number(+stream_or_alias, ?number)<BR>
read_number(?number)</TT></DD></DL><P><B>Description</B></P><P><TT>read_atom(SorA, Atom)</TT> succeeds if <TT>Atom</TT>
unifies with the next atom read from the stream associated with the
stream-term or alias <TT>SorA</TT>.</P><P><TT>read_integer(SorA, Integer)</TT> succeeds if
<TT>Integer</TT> unifies with the next integer read from the stream
associated with the stream-term or alias <TT>SorA</TT>.</P><P><TT>read_number(SorA, Number)</TT> succeeds if
<TT>Number</TT> unifies with the next number (integer or floating point
number) read from the stream associated with the stream-term or alias
<TT>SorA</TT>.</P><P><TT>read_atom/1</TT>, <TT>read_integer/1</TT> and <TT>read_number/1</TT>
apply to the current input stream.</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Atom</TT> is neither a variable nor an atom</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(atom, Atom)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Integer</TT> is neither a variable nor an integer</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(integer, Integer)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Number</TT> is neither a variable nor a number</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(number, Number)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is neither a variable nor a stream-term or alias</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(stream_or_alias, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is not associated with an open stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>existence_error(stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is an output stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(input, stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is associated with a binary stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(input, binary_stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> has stream properties <TT>end_of_stream(past)</TT>
and <TT>eof_action(error)</TT></TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(input, past_end_of_stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
a syntax error occurs and the value of the <TT>syntax_error</TT>
Prolog flag is <TT>error</TT> (section&#XA0;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>syntax_error(<I>atom explaining the error</I>)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
</TABLE><P><B>Portability</B></P><P>GNU Prolog predicates.</P><H4 CLASS="subsubsection"><A NAME="toc117"></A><A NAME="htoc153">7.14.3</A>&#XA0;&#XA0;<TT>read_token/2</TT>,
<TT>read_token/1</TT></H4><P>
<A NAME="read-token/2"></A>

</P><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
</DT><DD CLASS="dd-list"><TT>
read_token(+stream_or_alias, ?nonvar)<BR>
read_token(?nonvar)</TT></DD></DL><P><B>Description</B></P><P><TT>read_token(SorA, Token)</TT> succeeds if <TT>Token</TT> unifies with
the encoding of the next Prolog token read from the stream associated with
stream-term or alias <TT>SorA</TT>.</P><P><B>Token encoding</B>:</P><UL CLASS="itemize"><LI CLASS="li-itemize"><TT>var(A)</TT>: a variable is read whose name is the atom
<TT>A</TT>.</LI><LI CLASS="li-itemize">an atom <TT>A</TT>: an atom <TT>A</TT> is read.</LI><LI CLASS="li-itemize">integer <TT>N</TT>: an integer <TT>N</TT> is read.</LI><LI CLASS="li-itemize">floating point number <TT>N</TT>: a floating point number <TT>N</TT>
is read.</LI><LI CLASS="li-itemize"><TT>string(A)</TT>: a string (double quoted item) is read whose
characters forms the atom <TT>A</TT>. </LI><LI CLASS="li-itemize"><TT>punct(P)</TT>: a punctuation character <TT>P</TT> is read
(<TT>P</TT> is a one-character atom in <TT>()[]{|}</TT>, the atom
<TT>full_stop</TT> or the atom <TT>end_of_file</TT>).</LI><LI CLASS="li-itemize"><TT>back_quotes(A)</TT>: a back quoted item is read
whose characters forms the atom <TT>A</TT>.</LI><LI CLASS="li-itemize"><TT>extended(A)</TT>: an extended character <TT>A</TT> (an
atom) is read.</LI></UL><P>As for <TT>read_term/3</TT>, the behavior of <TT>read_token/2</TT> can be
affected by some Prolog flags (section&#XA0;<A HREF="#Term-input/output">7.14</A>).</P><P><TT>read_token/1</TT> applies to the current input stream.</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is neither a variable nor a stream-term or alias</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(stream_or_alias, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is not associated with an open stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>existence_error(stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is an output stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(input, stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is associated with a binary stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(input, binary_stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> has stream properties <TT>end_of_stream(past)</TT>
and <TT>eof_action(error)</TT></TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(input, past_end_of_stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
a syntax error occurs and the value of the <TT>syntax_error</TT>
Prolog flag is <TT>error</TT> (section&#XA0;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>syntax_error(<I>atom explaining the error</I>)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
</TABLE><P><B>Portability</B></P><P>GNU Prolog predicates.</P><H4 CLASS="subsubsection"><A NAME="toc118"></A><A NAME="htoc154">7.14.4</A>&#XA0;&#XA0;<TT>syntax_error_info/4</TT></H4><P>
<A NAME="syntax-error-info/4"></A>
</P><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
</DT><DD CLASS="dd-list"><TT>
syntax_error_info(?atom, ?integer, ?integer, ?atom)</TT></DD></DL><P><B>Description</B></P><P><TT>syntax_error_info(FileName, Line, Column, Error)</TT> returns the
information associated with the last syntax error. <TT>Line</TT> is the line
number of the error, <TT>Column</TT> is the column number of the error and
<TT>Error</TT> is an atom explaining the error.</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>FileName</TT> is neither a variable nor an atom</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(atom, FileName)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Line</TT> is neither a variable nor an integer</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(integer, Line)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Column</TT> is neither a variable nor an integer</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(integer, Column)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Error</TT> is neither a variable nor an atom</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(atom, Error)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
</TABLE><P><B>Portability</B></P><P>GNU Prolog predicate.</P><H4 CLASS="subsubsection"><A NAME="toc119"></A><A NAME="htoc155">7.14.5</A>&#XA0;&#XA0;<TT>last_read_start_line_column/2</TT></H4><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
</DT><DD CLASS="dd-list"><TT>
last_read_start_line_column(?integer, ?integer)</TT></DD></DL><P><B>Description</B></P><P><TT>last_read_start_line_column(Line, Column)</TT> unifies <TT>Line</TT>
and <TT>Column</TT> with the line number and the column number associated with
the start of the last read predicate. This predicate can be used after
calling one of the following predicates: <TT>read_term/3</TT>,
<TT>read_term/2</TT>, <TT>read/2</TT>, <TT>read/1</TT>
(section&#XA0;<A HREF="#read-term/3">7.14.1</A>), <TT>read_atom/2</TT>, <TT>read_atom/1</TT>,
<TT>read_integer/2</TT>, <TT>read_integer/1</TT>, <TT>read_number/2</TT>,
<TT>read_number/1</TT> (section&#XA0;<A HREF="#read-atom/2">7.14.2</A>) or <TT>read_token/2</TT>,
<TT>read_token/1</TT> (section&#XA0;<A HREF="#read-token/2">7.14.3</A>).</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Line</TT> is neither a variable nor an integer</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(integer, Line)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Column</TT> is neither a variable nor an integer</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(integer, Column)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
</TABLE><P><B>Portability</B></P><P>GNU Prolog predicate.</P><H4 CLASS="subsubsection"><A NAME="toc120"></A><A NAME="htoc156">7.14.6</A>&#XA0;&#XA0;<TT>write_term/3</TT>,
<TT>write_term/2</TT>,
<TT>write/2</TT>,
<TT>write/1</TT>,
<TT>writeq/2</TT>,
<TT>writeq/1</TT>,<BR>
 <TT>write_canonical/2</TT>,
<TT>write_canonical/1</TT>,
<TT>display/2</TT>,
<TT>display/1</TT>,
<TT>print/2</TT>,<BR>
 <TT>print/1</TT></H4><P>
<A NAME="write-term/3"></A>












</P><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
</DT><DD CLASS="dd-list"><TT>
write_term(+stream_or_alias, ?term, +write_option_list)<BR>
write_term(?term, +write_option_list)<BR>
write(+stream_or_alias, ?term)<BR>
write(?term)<BR>
writeq(+stream_or_alias, ?term)<BR>
writeq(?term)<BR>
write_canonical(+stream_or_alias, ?term)<BR>
write_canonical(?term)<BR>
display(+stream_or_alias, ?term)<BR>
display(?term)<BR>
print(+stream_or_alias, ?term)<BR>
print(?term)</TT></DD></DL><P><B>Description</B></P><P><TT>write_term(SorA, Term, Options)</TT> writes
<TT>Term</TT> to the stream associated with the stream-term or alias
<TT>SorA</TT> according to the options given by <TT>Options</TT>.</P><P><B>Write options</B>: <TT>Options</TT> is a list of write options. If this
list contains contradictory options, the rightmost option is the one which
applies. Possible options are:</P><UL CLASS="itemize"><LI CLASS="li-itemize"><TT>quoted(true</TT>/<TT>false)</TT>: if <TT>true</TT> each
atom and functor is quoted if this would be necessary for the term to be
input by <TT>read_term/3</TT>. If <TT>false</TT> no extra quotes are
written. The default value is <TT>false</TT>.</LI><LI CLASS="li-itemize"><TT>ignore_ops(true</TT>/<TT>false)</TT>: if
<TT>true</TT> each compound term is output in functional notation (neither
operator notation nor list notation is used). If <TT>false</TT> operator and
list notations are used. The default value is <TT>false</TT>.</LI><LI CLASS="li-itemize"><TT>numbervars(true</TT>/<TT>false)</TT>: if
<TT>true</TT> a term of the form <TT>&#X2019;$VAR&#X2019;(N)</TT>, where <TT>N</TT> is an
integer, is output as a variable name (see below). If <TT>false</TT>
such a term is output normally (according to the other options). The
default value is
<TT>true</TT>.</LI><LI CLASS="li-itemize"><TT>namevars(true</TT>/<TT>false)</TT>: if <TT>true</TT> a
term of the form <TT>&#X2019;$VARNAME&#X2019;(Name)</TT>, where <TT>Name</TT> is an atom,
is output as a variable name (see below). If <TT>false</TT> such a term is
output normally (according to the other options). The default value is
<TT>true</TT>.</LI><LI CLASS="li-itemize"><TT>space_args(true</TT>/<TT>false)</TT>: if
<TT>true</TT> an extra space character is emitted after each comma
separating the arguments of a compound term in functional notation or of a
list. If <TT>false</TT> no extra space is emitted. The default value is
<TT>false</TT>.</LI><LI CLASS="li-itemize"><TT>portrayed(true</TT>/<TT>false)</TT>: if <TT>true</TT>
and if there exists a predicate <TT>portray/1</TT>, <TT>write_term/3</TT>
acts as follows: if <TT>Term</TT> is a variable it is simply written. If
<TT>Term</TT> is non-variable then it is passed to <TT>portray/1</TT>. If
this succeeds then it is assumed that <TT>Term</TT> has been output.
Otherwise <TT>write_term/3</TT> outputs the principal functor of
<TT>Term</TT> (<TT>Term</TT> itself if it is atomic) according to other
options and recursively calls <TT>portray/1</TT> on the components of
<TT>Term</TT> (if it is a compound term). With <TT>ignore_ops(false)</TT> a
list is first passed to <TT>portray/1</TT> and only if this call fails each
element of the list is passed to <TT>portray/1</TT> (thus every sub-list is
not passed). The default value is <TT>false</TT>.</LI><LI CLASS="li-itemize"><TT>max_depth(N)</TT>: controls the depth of output for
compound terms. <TT>N</TT> is an integer specifying the depth. The output of
a term whose depth is greater than <TT>N</TT> gives rise to the output of
<TT>...</TT> (3 dots). By default there is no depth limit.</LI><LI CLASS="li-itemize"><TT>priority(N)</TT>: specifies the starting priority 
to output the term. This option controls if <TT>Term</TT> should be enclosed
in brackets. <TT>N</TT> is a positive integer &#X2264; 1200. By default
<TT>N</TT> = 1200.</LI></UL><P><B>Variable numbering</B>: when the <TT>numbervars(true)</TT> option is
passed to <TT>write_term/3</TT> any term of the form <TT>&#X2019;$VAR&#X2019;(N)</TT>
where <TT>N</TT> is an integer is output as a variable name consisting of a
capital letter possibly followed by an integer. The capital letter is the
<TT>(I+1)</TT><EM>th</EM> letter of the alphabet and the integer is
<TT>J</TT>, where <TT>I = N mod 26</TT> and <TT>J = N // 26</TT>. The
integer <TT>J</TT> is omitted if it is zero. For example: </P><DL CLASS="list"><DT CLASS="dt-list">
</DT><DD CLASS="dd-list"><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD ALIGN=left NOWRAP><TT>&#X2019;$VAR&#X2019;(0)</TT></TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD ALIGN=left NOWRAP>is written as <TT>A</TT></TD></TR>
<TR><TD ALIGN=left NOWRAP><TT>&#X2019;$VAR&#X2019;(1)</TT></TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD ALIGN=left NOWRAP>is written as <TT>B</TT></TD></TR>
<TR><TD ALIGN=left NOWRAP COLSPAN=3><TT>...</TT></TD></TR>
<TR><TD ALIGN=left NOWRAP><TT>&#X2019;$VAR&#X2019;(25)</TT></TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD ALIGN=left NOWRAP>is written as <TT>Z</TT></TD></TR>
<TR><TD ALIGN=left NOWRAP><TT>&#X2019;$VAR&#X2019;(26)</TT></TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD ALIGN=left NOWRAP>is written as <TT>A1</TT></TD></TR>
<TR><TD ALIGN=left NOWRAP><TT>&#X2019;$VAR&#X2019;(27)</TT></TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD ALIGN=left NOWRAP>is written as <TT>B1</TT></TD></TR>
</TABLE></DD></DL><P><B>Variable naming</B>: when the <TT>namevars(true)</TT> option is passed
to <TT>write_term/3</TT> any term of the form <TT>&#X2019;$VARNAME&#X2019;(Name)</TT>
where <TT>Name</TT> is an atom is output as a variable name consisting of
the characters <TT>Name</TT>. For example: <TT>&#X2019;$VARNAME&#X2019;(&#X2019;A&#X2019;)</TT> is
written as <TT>A</TT> (even in the presence of the <TT>quoted(true)</TT>
option).</P><P><TT>write(SorA, Term)</TT> is equivalent to
<TT>write_term(SorA, Term, [])</TT>.</P><P><TT>writeq(SorA, Term)</TT> is equivalent to
<TT>write_term(SorA, Term, [quoted(true)])</TT>.</P><P><TT>write_canonical(SorA, Term)</TT> is equivalent to
<TT>write_term(SorA, Term, [quoted(true),<BR>
ignore_ops(true), numbervars(false)])</TT>.</P><P><TT>display(SorA, Term)</TT> is equivalent to
<TT>write_term(SorA, Term, [ignore_ops(true),<BR>
numbervars(false)])</TT>.</P><P><TT>print(SorA, Term)</TT> is equivalent to
<TT>write_term(SorA, Term, [numbervars(false),<BR>
portrayed(true)])</TT>.</P><P><TT>write_term/2</TT>, <TT>write/1</TT>, <TT>writeq/1</TT>,
<TT>write_canonical/1</TT>, <TT>display/1</TT> and <TT>print/1</TT> apply
to the current output stream.</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Options</TT> is a partial list or a list with an element
<TT>E</TT> which is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Options</TT> is neither a partial list nor a list</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(list, Options)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is neither a variable nor a stream-term or alias</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(stream_or_alias, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
an element <TT>E</TT> of the <TT>Options</TT> list is neither a
variable nor a valid write-option</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(write_option, E)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is not associated with an open stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>existence_error(stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is an input stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(output, stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is associated with a binary stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(output, binary_stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
</TABLE><P><B>Portability</B></P><P>ISO predicates except <TT>display/1-2</TT> and <TT>print/1-2</TT> that
are GNU Prolog predicates. <TT>namevars/1</TT>, <TT>space_args/1</TT>,
<TT>portrayed/1</TT>, <TT>max_depth/1</TT> and <TT>priority/1</TT>
options are GNU Prolog extensions.</P><H4 CLASS="subsubsection"><A NAME="toc121"></A><A NAME="htoc157">7.14.7</A>&#XA0;&#XA0;<TT>format/3</TT>,
<TT>format/2</TT></H4><P>
<A NAME="format/3"></A>

</P><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
</DT><DD CLASS="dd-list"><TT>
format(+stream_or_alias, +character_code_list_or_atom,
+list)<BR>
format(+character_code_list_or_atom, +list)</TT></DD></DL><P><B>Description</B></P><P><TT>format(SorA, Format, Arguments)</TT> writes the <TT>Format</TT> string
replacing each format control sequence <TT>F</TT> by the corresponding
element of <TT>Arguments</TT> (formatted according to <TT>F</TT>) to the
stream associated with the stream-term or alias <TT>SorA</TT>.</P><P><B>Format control sequences</B>: the general format of a control sequence
is <TT>&#X2019;~NC&#X2019;</TT>. The character <TT>C</TT> determines the type of
the control sequence. <TT>N</TT> is an optional numeric argument. An
alternative form of <TT>N</TT> is <TT>&#X2019;*&#X2019;</TT>. <TT>&#X2019;*&#X2019;</TT> implies
that the next argument <TT>Arg</TT> in <TT>Arguments</TT> should be
used as a numeric argument in the control sequence. The use of C
<TT>printf()</TT> formatting sequence (beginning by the character
<TT>%</TT>) is also allowed. The following control sequences are
available:</P><TABLE BORDER=1 CELLSPACING=0 CELLPADDING=1><TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
Format sequence</DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">type of the argument</DIV></TD><TD VALIGN=top ALIGN=left>Description</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~Na</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">atom</DIV></TD><TD VALIGN=top ALIGN=left>print the atom without quoting. <TT>N</TT> is minimal number of characters to print using spaces on the rigth if needed (default: the length of the atom)</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~Nc</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">character code</DIV></TD><TD VALIGN=top ALIGN=left>print the character associated with the
code. <TT>N</TT> is the number of times to print the character (default: 1)</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT> ~Nf</TT>
<BR>
<TT>~Ne ~NE ~Ng ~NG</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">float expression</DIV></TD><TD VALIGN=top ALIGN=left>pass the argument <TT>Arg</TT> and 
<TT>N</TT> to the C <TT>printf()</TT>
function as: 
<BR>
if <TT>N</TT> is not specified 
<TT>printf("%f",Arg)</TT> else
<TT>printf("%.Nf",Arg)</TT>.
<BR>
Similarly for <TT>~Ne</TT>, <TT>~NE</TT>, <TT>~Ng</TT> and <TT>~NG</TT></TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~Nd</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">integer expression</DIV></TD><TD VALIGN=top ALIGN=left>print the argument. <TT>N</TT> is the
number of digits after the decimal point. If <TT>N</TT> is 0 no
decimal point is printed (default: 0)</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~ND</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">integer expression</DIV></TD><TD VALIGN=top ALIGN=left>identical to <TT>~Nd</TT> except
that <TT>&#X2019;,&#X2019;</TT> separates groups of three digits to the left of the
decimal point</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~Nr</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">integer expression</DIV></TD><TD VALIGN=top ALIGN=left>print the argument according to the
radix <TT>N</TT>. 2 &#X2264; <TT>N</TT> &#X2264; 36 (default: 8). The letters
<TT>a-z</TT> denote digits &gt; 9</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~NR</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">integer expression</DIV></TD><TD VALIGN=top ALIGN=left>identical to <TT>~Nr</TT> except
that the letters <TT>A-Z</TT> denote digits &gt; 9</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~Ns</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">character code list</DIV></TD><TD VALIGN=top ALIGN=left>print exactly <TT>N</TT> characters 
(default: the length of the list)</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~NS</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">character list</DIV></TD><TD VALIGN=top ALIGN=left>print exactly <TT>N</TT> characters
(default: the length of the list)</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~i</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">term</DIV></TD><TD VALIGN=top ALIGN=left>ignore the current argument</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~k</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">term</DIV></TD><TD VALIGN=top ALIGN=left>pass the argument to
<TT>write_canonical/1</TT> (section&#XA0;<A HREF="#write-term/3">7.14.6</A>)</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~p</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">term</DIV></TD><TD VALIGN=top ALIGN=left>pass the argument to <TT>print/1</TT>
(section&#XA0;<A HREF="#write-term/3">7.14.6</A>)</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~q</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">term</DIV></TD><TD VALIGN=top ALIGN=left>pass the argument to <TT>writeq/1</TT>
(section&#XA0;<A HREF="#write-term/3">7.14.6</A>)</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~w</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">term</DIV></TD><TD VALIGN=top ALIGN=left>pass the argument to <TT>write/1</TT>
(section&#XA0;<A HREF="#write-term/3">7.14.6</A>)</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~~</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">none</DIV></TD><TD VALIGN=top ALIGN=left>print the character <TT>&#X2019;~&#X2019;</TT></TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~Nn</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">none</DIV></TD><TD VALIGN=top ALIGN=left>print <TT>N</TT> new-line characters (default: 1)</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~N</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">none</DIV></TD><TD VALIGN=top ALIGN=left>print a new-line character if not at the beginning
of a line</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>~?</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">atom</DIV></TD><TD VALIGN=top ALIGN=left>use the argument as a nested format string</TD></TR>
<TR><TD VALIGN=top ALIGN=left><DIV CLASS="center">
<TT>%F</TT></DIV></TD><TD VALIGN=top ALIGN=left><DIV CLASS="center">atom, integer or float expression</DIV></TD><TD VALIGN=top ALIGN=left>interface to the C
function <TT>printf(3)</TT> for outputting atoms (C string), integers and
floating point numbers. <TT>*</TT> are also allowed.</TD></TR>
</TABLE><P><TT>format/2</TT> applies to the current output stream.</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Format</TT> is a partial list or a list with an element
<TT>E</TT> which is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Arguments</TT> is a partial list</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Format</TT> is neither a partial list nor a list or an atom</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(list, Format)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Arguments</TT> is neither a partial list nor a list</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(list, Arguments)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
an element <TT>E</TT> of the <TT>Format</TT> list is neither a
variable nor a character code</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>representation_error(character_code, E)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is neither a variable nor a stream-term or alias</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(stream_or_alias, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
an element <TT>E</TT> of Format is not a valid format control
sequence</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(format_control_sequence, E)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
the <TT>Arguments</TT> list does not contain sufficient elements</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(non_empty_list, [])</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
an element <TT>E</TT> of the <TT>Arguments</TT> list is a variable
while a non-variable term was expected</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
an element <TT>E</TT> of the <TT>Arguments</TT> list is neither
variable nor an atom while an atom was expected</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(atom, E)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
an element <TT>E</TT> of the <TT>Arguments</TT> cannot be evaluated
as an arithmetic expression while an integer or a floating point number was
expected</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left>an arithmetic error (section&#XA0;<A HREF="gprolog029.html#Evaluation-of-an-arithmetic-expression">7.6.1</A>)</TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
an element <TT>E</TT> of the <TT>Arguments</TT> list is neither
variable nor character code while a character code was expected</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>representation_error(character_code, E)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is not associated with an open stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>existence_error(stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is an input stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(output, stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is associated with a binary stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(output, binary_stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
</TABLE><P><B>Portability</B></P><P>GNU Prolog predicates. </P><H4 CLASS="subsubsection"><A NAME="toc122"></A><A NAME="htoc158">7.14.8</A>&#XA0;&#XA0;<TT>portray_clause/2</TT>,
<TT>portray_clause/1</TT></H4><P>
<A NAME="portray-clause/2"></A>

</P><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
</DT><DD CLASS="dd-list"><TT>
portray_clause(+stream_or_alias, +clause)<BR>
portray_clause(+clause)</TT></DD></DL><P><B>Description</B></P><P><TT>portray_clause(SorA, Clause)</TT> pretty prints
<TT>Clause</TT> to the stream associated with the stream-term or alias
<TT>SorA</TT>.
<TT>portray_clause/2</TT> uses the variable binding predicates
<TT>name_singleton_vars/1</TT> (section&#XA0;<A HREF="gprolog028.html#name-singleton-vars/1">7.5.1</A>) and
<TT>numbervars/1</TT> (section&#XA0;<A HREF="gprolog028.html#bind-variables/2">7.5.3</A>). This predicate is
used by <TT>listing/1</TT> (section&#XA0;<A HREF="gprolog046.html#listing/1">7.23.3</A>).</P><P><TT>portray_clause/1</TT> applies to the current output stream.</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Clause</TT> is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Clause</TT> is neither a variable nor a callable term</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(callable, Clause)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is neither a variable nor a stream-term or alias</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(stream_or_alias, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is not associated with an open stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>existence_error(stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is an input stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(output, stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>SorA</TT> is associated with a binary stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(output, binary_stream, SorA)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
</TABLE><P><B>Portability</B></P><P>GNU Prolog predicates.</P><H4 CLASS="subsubsection"><A NAME="toc123"></A><A NAME="htoc159">7.14.9</A>&#XA0;&#XA0;<TT>get_print_stream/1</TT></H4><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
</DT><DD CLASS="dd-list"><TT>
get_print_stream(?stream)</TT></DD></DL><P><B>Description</B></P><P><TT>get_print_stream(Stream)</TT> unifies <TT>Stream</TT> with the
stream-term associated with the output stream used by <TT>print/2</TT>
(section&#XA0;<A HREF="#write-term/3">7.14.6</A>). The purpose of this predicate is to allow a
user-defined <TT>portray/1</TT> predicate to identify the output stream in
use.</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Stream</TT> is neither a variable nor a stream-term</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(stream, Stream)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
</TABLE><P><B>Portability</B></P><P>GNU Prolog predicate.</P><H4 CLASS="subsubsection"><A NAME="toc124"></A><A NAME="htoc160">7.14.10</A>&#XA0;&#XA0;<TT>op/3</TT></H4><P>
<A NAME="op/3:(Term-input/output)"></A>
</P><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
</DT><DD CLASS="dd-list"><TT>
op(+integer, +operator_specifier, +atom_or_atom_list)</TT></DD></DL><P><B>Description</B></P><P><TT>op(Priority, OpSpecifier, Operator)</TT> alters the operator table.
<TT>Operator</TT> is declared as an operator with properties defined by
specifier <TT>OpSpecifier</TT> and <TT>Priority</TT>. <TT>Priority</TT> must
be an integer &#X2265; 0 and &#X2264; 1200. If <TT>Priority</TT> is 0 then the
operator properties of <TT>Operator</TT> (if any) are canceled.
<TT>Operator</TT> may also be a list of atoms in which case all of them are
declared to be operators. In general, operators can be removed from
the operator table and their priority or specifier can be changed. However,
it is an error to attempt to change the <TT>&#X2019;,&#X2019;</TT> operator from its
initial status. An atom can have multiple operator definitions (e.g.
prefix and infix like <TT>+</TT>) however an atom cannot have both an
infix and a postfix operator definitions.</P><P><B>Operator specifiers</B>: the following specifiers are available:</P><TABLE BORDER=1 CELLSPACING=0 CELLPADDING=1><TR><TD ALIGN=center NOWRAP>
Specifier</TD><TD ALIGN=center NOWRAP>Type</TD><TD ALIGN=center NOWRAP>Associativity</TD></TR>
<TR><TD ALIGN=center NOWRAP>
<TT>fx</TT></TD><TD ALIGN=center NOWRAP>prefix</TD><TD ALIGN=center NOWRAP>no</TD></TR>
<TR><TD ALIGN=center NOWRAP>
<TT>fy</TT></TD><TD ALIGN=center NOWRAP>prefix</TD><TD ALIGN=center NOWRAP>yes</TD></TR>
<TR><TD ALIGN=center NOWRAP>
<TT>xf</TT></TD><TD ALIGN=center NOWRAP>postfix</TD><TD ALIGN=center NOWRAP>no</TD></TR>
<TR><TD ALIGN=center NOWRAP>
<TT>yf</TT></TD><TD ALIGN=center NOWRAP>postfix</TD><TD ALIGN=center NOWRAP>yes</TD></TR>
<TR><TD ALIGN=center NOWRAP>
<TT>xfx</TT></TD><TD ALIGN=center NOWRAP>infix</TD><TD ALIGN=center NOWRAP>no</TD></TR>
<TR><TD ALIGN=center NOWRAP>
<TT>yfx</TT></TD><TD ALIGN=center NOWRAP>infix</TD><TD ALIGN=center NOWRAP>left</TD></TR>
<TR><TD ALIGN=center NOWRAP>
<TT>xfy</TT></TD><TD ALIGN=center NOWRAP>infix</TD><TD ALIGN=center NOWRAP>right</TD></TR>
</TABLE><P><B>Prolog predefined operators</B>:</P><TABLE BORDER=1 CELLSPACING=0 CELLPADDING=1><TR><TD VALIGN=top ALIGN=right NOWRAP>
Priority</TD><TD VALIGN=top ALIGN=center NOWRAP>Specifier</TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft">Operators</DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>1200</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>xfx</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>:- &#XA0;--&gt;</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>1200</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>fx</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>:-</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>1100</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>xfy</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>;</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>1050</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>xfy</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>-&gt;</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>1000</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>xfy</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>,</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>900</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>fy</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>\+</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>700</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>xfx</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>= &#XA0;\= &#XA0;=.. &#XA0;== &#XA0;\== &#XA0;@&lt;
&#XA0;@=&lt; &#XA0;@&gt; &#XA0;@&gt;= &#XA0;is &#XA0;=:= &#XA0;=\= &#XA0;&lt; &#XA0;=&lt; &#XA0;&gt; &#XA0;&gt;=</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>600</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>xfy</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>:</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>500</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>yfx</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>+ &#XA0;- &#XA0;/\ &#XA0;\/</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>400</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>yfx</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>* &#XA0;/ &#XA0;// &#XA0;rem &#XA0;mod &#XA0;&lt;&lt;
&#XA0;&gt;&gt;</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>200</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>xfy</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>** &#XA0;^</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>200</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>fy</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>+ &#XA0;- &#XA0;\</TT></DIV></TD></TR>
</TABLE><P><B>FD predefined operators</B>:</P><TABLE BORDER=1 CELLSPACING=0 CELLPADDING=1><TR><TD VALIGN=top ALIGN=right NOWRAP>
Priority</TD><TD VALIGN=top ALIGN=center NOWRAP>Specifier</TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft">Operators</DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>750</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>xfy</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>#&lt;=&gt; &#XA0;#\&lt;=&gt;</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>740</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>xfy</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>#==&gt; &#XA0;#\==&gt;</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>730</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>xfy</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>## &#XA0;#\/ &#XA0;#\\/</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>720</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>yfx</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>#/\ &#XA0;#\/\</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>710</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>fy</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>#\</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>700</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>xfx</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>#= &#XA0;#\= &#XA0;#&lt; &#XA0;#=&lt;
&#XA0;#&gt; &#XA0;#&gt;= &#XA0;#=# &#XA0;#\=# &#XA0;#&lt;# &#XA0;#=&lt;# &#XA0;#&gt;#
&#XA0;#&gt;=#</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>500</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>yfx</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>+ &#XA0;-</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>400</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>yfx</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>* &#XA0;/ &#XA0;// &#XA0;rem</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>200</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>xfy</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>**</TT></DIV></TD></TR>
<TR><TD VALIGN=top ALIGN=right NOWRAP>
<TT>200</TT></TD><TD VALIGN=top ALIGN=center NOWRAP><TT>fy</TT></TD><TD VALIGN=top ALIGN=left><DIV CLASS="flushleft"><TT>+ &#XA0;-</TT></DIV></TD></TR>
</TABLE><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Priority</TT> is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>OpSpecifier</TT> is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Operator</TT> is a partial list or a list with an element
<TT>E</TT> which is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Priority</TT> is neither a variable nor an integer</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(integer, Priority)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>OpSpecifier</TT> is neither a variable nor an atom</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(atom, OpSpecifier)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Operator</TT> is neither a partial list nor a list nor an atom</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(list, Operator)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
an element <TT>E</TT> of the <TT>Operator</TT> list is neither a
variable nor an atom</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(atom, E)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Priority</TT> is an integer not &#X2265; 0 and &#X2264; 1200</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(operator_priority, Priority)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>OpSpecifier</TT> is not a valid operator specifier</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(operator_specifier, OpSpecifier)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Operator</TT> is <TT>&#X2019;,&#X2019;</TT> or an element of the
<TT>Operator</TT> list is <TT>&#X2019;,&#X2019;</TT></TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(modify, operator, &#X2019;,&#X2019;)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>OpSpecifier</TT> is a specifier such that <TT>Operator</TT>
would have a postfix and an infix definition.</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>permission_error(create, operator, Operator)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
</TABLE><P><B>Portability</B></P><P>ISO predicate. </P><P>The ISO reference implies that if a program calls <TT>current_op/3</TT>,
then modifies an operator definition by calling <TT>op/3</TT> and backtracks
into the call to <TT>current_op/3</TT>, then the changes are guaranteed not
to affect that <TT>current_op/3</TT> goal. This is not guaranteed by
GNU Prolog.</P><H4 CLASS="subsubsection"><A NAME="toc125"></A><A NAME="htoc161">7.14.11</A>&#XA0;&#XA0;<TT>current_op/3</TT></H4><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
</DT><DD CLASS="dd-list"><TT>
current_op(?integer, ?operator_specifier, ?atom)</TT></DD></DL><P><B>Description</B></P><P><TT>current_op(Priority, OpSpecifier, Operator)</TT> succeeds if
<TT>Operator</TT> is an operator with properties defined by specifier
<TT>OpSpecifier</TT> and <TT>Priority</TT>. This predicate is re-executable
on backtracking.</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Priority</TT> is neither a variable nor an operator priority</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(operator_priority, Priority)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>OpSpecifier</TT> is neither a variable nor an operator
specifier</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(operator_specifier, OpSpecifier)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>Operator</TT> is neither a variable nor an atom</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(atom, Operator)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
</TABLE><P><B>Portability</B></P><P>ISO predicate. </P><H4 CLASS="subsubsection"><A NAME="toc126"></A><A NAME="htoc162">7.14.12</A>&#XA0;&#XA0;<TT>char_conversion/2</TT></H4><P>
<A NAME="char-conversion/2"></A>
</P><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
</DT><DD CLASS="dd-list"><TT>
char_conversion(+character, +character)</TT></DD></DL><P><B>Description</B></P><P><TT>char_conversion(InChar, OutChar)</TT> alters the character-conversion
mapping. This mapping is used by the following read predicates:
<TT>read_term/3</TT> (section&#XA0;<A HREF="#read-term/3">7.14.1</A>), <TT>read_atom/2</TT>,
<TT>read_integer/2</TT>, <TT>read_number/2</TT> (section&#XA0;<A HREF="#read-atom/2">7.14.2</A>) and
<TT>read_token/2</TT> (section&#XA0;<A HREF="#read-token/2">7.14.3</A>) to replace any occurrence of a
character <TT>InChar</TT> by <TT>OutChar</TT>. However the conversion
mechanism should have been previously activated by switching on the
<TT>char_conversion</TT> Prolog flag (section&#XA0;<A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>). When
<TT>InChar</TT> and <TT>OutChar</TT> are the same, the effect is to remove
any conversion of a character <TT>InChar</TT>.</P><P>Note that the single character read predicates (e.g. <TT>get_char/2</TT>)
never do character conversion. If such behavior is required, it must be
explicitly done using <TT>current_char_conversion/2</TT>
(section&#XA0;<A HREF="#current-char-conversion/2">7.14.13</A>).</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>InChar</TT> is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>OutChar</TT> is a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>InChar</TT> is neither a variable nor a character</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(character, InChar)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>OutChar</TT> is neither a variable nor a character</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(character, OutChar)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
</TABLE><P><B>Portability</B></P><P>ISO predicate. The <TT>type_error(character,&#X2026;)</TT> is a GNU Prolog
behavior, the ISO reference instead defines a
<TT>representation_error(character)</TT> in this case. This seems to be an
error of the ISO reference since, for many other built-in predicates
accepting a character (e.g. <TT>char_code/2</TT>, <TT>put_char/2</TT>), a
<TT>type_error</TT> is raised. </P><P>The ISO reference implies that if a program calls
<TT>current_char_conversion/2</TT>, then modifies the character mapping by
calling <TT>char_conversion/2</TT>, and backtracks into the call to
<TT>current_char_conversion/2</TT> then the changes are guaranteed not to
affect that <TT>current_char_conversion/2</TT> goal. This is not guaranteed
by GNU Prolog.</P><H4 CLASS="subsubsection"><A NAME="toc127"></A><A NAME="htoc163">7.14.13</A>&#XA0;&#XA0;<TT>current_char_conversion/2</TT></H4><P>
<A NAME="current-char-conversion/2"></A>
</P><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
</DT><DD CLASS="dd-list"><TT>
current_char_conversion(?character, ?character)</TT></DD></DL><P><B>Description</B></P><P><TT>current_char_conversion(InChar, OutChar)</TT> succeeds if the
conversion of <TT>InChar</TT> is <TT>OutChar</TT> according to the
character-conversion mapping. In that case, <TT>InChar</TT> and
<TT>OutChar</TT> are different. This predicate is re-executable on
backtracking.</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>InChar</TT> is neither a variable nor a character</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(character, InChar)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
<TR><TD VALIGN=top ALIGN=left>
<TT>OutChar</TT> is neither a variable nor a character</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(character, OutChar)</TT></TD></TR>
<TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
</TABLE><P><B>Portability</B></P><P>ISO predicate. Same remark as for char_conversion/2
(section&#XA0;<A HREF="#char-conversion/2">7.14.12</A>).</P>
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