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Atomic term processing
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<H3 CLASS="subsection"><A NAME="htoc187">7.19</A> Atomic term processing</H3><UL>
<LI><A HREF="gprolog042.html#toc147"><TT>atom_length/2</TT></A>
<LI><A HREF="gprolog042.html#toc148"><TT>atom_concat/3</TT></A>
<LI><A HREF="gprolog042.html#toc149"><TT>sub_atom/5</TT></A>
<LI><A HREF="gprolog042.html#toc150"><TT>char_code/2</TT></A>
<LI><A HREF="gprolog042.html#toc151"><TT>lower_upper/2</TT></A>
<LI><A HREF="gprolog042.html#toc152"><TT>atom_chars/2</TT>,
<TT>atom_codes/2</TT></A>
<LI><A HREF="gprolog042.html#toc153"><TT>number_atom/2</TT>,
<TT>number_chars/2</TT>,
<TT>number_codes/2</TT></A>
<LI><A HREF="gprolog042.html#toc154"><TT>name/2</TT></A>
<LI><A HREF="gprolog042.html#toc155"><TT>atom_hash/2</TT></A>
<LI><A HREF="gprolog042.html#toc156"><TT>new_atom/3</TT>,
<TT>new_atom/2</TT>,
<TT>new_atom/1</TT></A>
<LI><A HREF="gprolog042.html#toc157"><TT>current_atom/1</TT></A>
<LI><A HREF="gprolog042.html#toc158"><TT>atom_property/2</TT></A>
</UL>
These built-in predicates enable atomic terms to be processed as a sequence
of characters and character codes. Facilities exist to split and join atoms,
to convert a single character to and from the corresponding character code,
and to convert a number to and from a list of characters and character
codes.<BR>
<BR>
<A NAME="toc147"></A>
<H4 CLASS="subsubsection"><A NAME="htoc188">7.19.1</A> <TT>atom_length/2</TT></H4>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
atom_length(+atom, ?integer)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>atom_length(Atom, Length)</TT> succeeds if <TT>Length</TT> unifies with
the number of characters of the name of <TT>Atom</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Atom</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></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> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Atom)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Length</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Length)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Length</TT> is an integer < 0</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(not_less_than_zero, Length)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
ISO predicate.<BR>
<BR>
<A NAME="toc148"></A>
<H4 CLASS="subsubsection"><A NAME="htoc189">7.19.2</A> <TT>atom_concat/3</TT></H4>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
atom_concat(+atom, +atom, ?atom)<BR>
atom_concat(?atom, ?atom, +atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>atom_concat(Atom1, Atom2, Atom12)</TT> succeeds if the name of
<TT>Atom12</TT> is the concatenation of the name of <TT>Atom1</TT> with the
name of <TT>Atom1</TT>. This predicate is re-executable on backtracking
(e.g. if <TT>Atom12</TT> is instantiated and both <TT>Atom1</TT> and
<TT>Atom2</TT> are variables).<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Atom1</TT> and <TT>Atom12</TT> are variables</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Atom2</TT> and <TT>Atom12</TT> are variables</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Atom1</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Atom1)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Atom2</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Atom2)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Atom12</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Atom12)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
ISO predicate.<BR>
<BR>
<A NAME="toc149"></A>
<H4 CLASS="subsubsection"><A NAME="htoc190">7.19.3</A> <TT>sub_atom/5</TT></H4>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
sub_atom(+atom, ?integer, ?integer, ?integer, ?atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>sub_atom(Atom, Before, Length, After, SubAtom)</TT> succeeds if atom
<TT>Atom</TT> can be split into three atoms, <TT>AtomL</TT>,
<TT>SubAtom</TT> and <TT>AtomR</TT> such that <TT>Before</TT> is the number
of characters of the name of <TT>AtomL</TT>, <TT>Length</TT> is the number
of characters of the name of <TT>SubAtom</TT> and <TT>After</TT> is the
number of characters of the name of <TT>AtomR</TT>. This predicate is
re-executable on backtracking.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Atom</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></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> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Atom)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>SubAtom</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, SubAtom)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Before</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Before)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Length</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Length)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>After</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, After)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Before</TT> is an integer < 0</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(not_less_than_zero, Before)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Length</TT> is an integer < 0</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(not_less_than_zero, Length)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>After</TT> is an integer < 0</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(not_less_than_zero, After)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
ISO predicate.<BR>
<BR>
<A NAME="toc150"></A>
<H4 CLASS="subsubsection"><A NAME="htoc191">7.19.4</A> <TT>char_code/2</TT></H4>
<A NAME="char-code/2"></A>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
char_code(+character, ?character_code)<BR>
char_code(-character, +character_code)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>char_code(Char, Code)</TT> succeeds if the character code for the
one-char atom <TT>Char</TT> is <TT>Code</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Char</TT> and <TT>Code</TT> are variables</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Char</TT> is neither a variable nor a one-char atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(character, Char)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Code</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Code)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Code</TT> is an integer but not a character code</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>representation_error(character_code)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
ISO predicate.<BR>
<BR>
<A NAME="toc151"></A>
<H4 CLASS="subsubsection"><A NAME="htoc192">7.19.5</A> <TT>lower_upper/2</TT></H4>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
lower_upper(+character, ?character)<BR>
lower_upper(-character, +character)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>lower_upper(Char1, Char2)</TT> succeeds if <TT>Char1</TT> and
<TT>Char2</TT> are one-char atoms and if <TT>Char2</TT> is the upper
conversion of <TT>Char1</TT>. If <TT>Char1</TT> (resp. <TT>Char2</TT>) is a
character that is not a lower (resp. upper) letter then <TT>Char2</TT> is
equal to <TT>Char1</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Char1</TT> and <TT>Char2</TT> are variables</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Char1</TT> is neither a variable nor a one-char atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(character, Char1)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Char2</TT> is neither a variable nor a one-char atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(character, Char2)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc152"></A>
<H4 CLASS="subsubsection"><A NAME="htoc193">7.19.6</A> <TT>atom_chars/2</TT>,
<TT>atom_codes/2</TT></H4>
<A NAME="atom-chars/2"></A>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
atom_chars(+atom, ?character_list)<BR>
atom_chars(-atom, +character_list)<BR>
atom_codes(+atom, ?character_code_list)<BR>
atom_codes(-atom, +character_code_list)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>atom_chars(Atom, Chars)</TT> succeeds if <TT>Chars</TT>
is the list of one-char atoms whose names are the successive characters of
the name of <TT>Atom</TT>.<BR>
<BR>
<TT>atom_codes(Atom, Codes)</TT> is similar to
<TT>atom_chars/2</TT> but deals with a list of character codes.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Atom</TT> is a variable and <TT>Chars</TT> (or <TT>Codes</TT>)
is a partial list or a list with an element which is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></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> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Atom)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Chars</TT> is neither a list nor a partial list</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(list, Chars)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Codes</TT> is neither a list nor a partial list</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(list, Codes)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Atom</TT> is a variable and an element <TT>E</TT> of the list
<TT>Chars</TT> is neither a variable nor a one-char atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(character, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Atom</TT> is a variable and an element <TT>E</TT> of the list
<TT>Codes</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Atom</TT> is a variable and an element <TT>E</TT> of the list
<TT>Codes</TT> is an integer but not a character code</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>representation_error(character_code)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
ISO predicates. The ISO reference only causes a <TT>type_error(list,
Chars)</TT> if <TT>Atom</TT> is a variable and <TT>Chars</TT> is neither a list
nor a partial list. GNU Prolog always checks if <TT>Chars</TT> is a list.
Similarly for <TT>Codes</TT>. The <TT>type_error(integer, E)</TT> when an
element <TT>E</TT> of the <TT>Codes</TT> is not an integer is a GNU Prolog
extension. This seems to be an omission in the ISO reference since this
error is detected for many other built-in predicates accepting a character
code (e.g. <TT>char_code/2</TT>, <TT>put_code/2</TT>).<BR>
<BR>
<A NAME="toc153"></A>
<H4 CLASS="subsubsection"><A NAME="htoc194">7.19.7</A> <TT>number_atom/2</TT>,
<TT>number_chars/2</TT>,
<TT>number_codes/2</TT></H4>
<A NAME="number-atom/2"></A>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
number_atom(+number, ?atom)<BR>
number_atom(-number, +atom)<BR>
number_chars(+number, ?character_list)<BR>
number_chars(-number, +character_list)<BR>
number_codes(+number, ?character_code_list)<BR>
number_codes(-number, +character_code_list)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>number_atom(Number, Atom)</TT> succeeds if
<TT>Atom</TT> is an atom whose name corresponds to the characters of
<TT>Number</TT>.<BR>
<BR>
<TT>number_chars(Number, Chars)</TT> is similar to
<TT>number_atom/2</TT> but deals with a list of character codes.<BR>
<BR>
<TT>number_codes(Number, Codes)</TT> is similar to
<TT>number_atom/2</TT> but deals with a list of characters.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Number</TT> and <TT>Atom</TT> are variables</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Number</TT> is a variable and <TT>Chars</TT> (or
<TT>Codes</TT>) is a partial list or a list with an element which is a
variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Number</TT> is neither a variable nor an number</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(number, Number)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></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> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Atom)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Number</TT> is a variable and <TT>Chars</TT> is neither a list
nor a partial list</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(list, Chars)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Number</TT> is a variable and <TT>Codes</TT> is neither a list
nor a partial list</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(list, Codes)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Number</TT> is a variable and an element <TT>E</TT> of the list
<TT>Chars</TT> is neither a variable nor a one-char atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(character, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Number</TT> is a variable and an element <TT>E</TT> of the list
<TT>Codes</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Number</TT> is a variable and an element <TT>E</TT> of the list
<TT>Codes</TT> is an integer but not a character code</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>representation_error(character_code)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Number</TT> is a variable, <TT>Atom</TT> (or <TT>Chars</TT> or
<TT>Codes</TT>) cannot be parsed as a number and the value of the
<TT>syntax_error</TT> Prolog flag is <TT>error</TT>
(section <A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>)</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>syntax_error(<I>atom explaining the error</I>)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
<TT>number_atom/2</TT> is a GNU Prolog predicate. <TT>number_chars/2</TT>
and <TT>number_codes/2</TT> are ISO predicates.<BR>
<BR>
GNU Prolog only raises an error about an element <TT>E</TT> of the
<TT>Chars</TT> (or <TT>Codes</TT>) list when <TT>Number</TT> is a variable
while the ISO reference always check this. This seems an error since
the list itself is only checked if <TT>Number</TT> is a variable.<BR>
<BR>
The <TT>type_error(integer, E)</TT> when an element <TT>E</TT> of the
<TT>Codes</TT> is not an integer is a GNU Prolog extension. This seems to be
an omission in the ISO reference since this error is detected for many other
built-in predicates accepting a character code (e.g. <TT>char_code/2</TT>,
<TT>put_code/2</TT>).<BR>
<BR>
<A NAME="toc154"></A>
<H4 CLASS="subsubsection"><A NAME="htoc195">7.19.8</A> <TT>name/2</TT></H4>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
name(+atomic, ?character_code_list)<BR>
name(-atomic, +character_code_list)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>name(Constant, Codes)</TT> succeeds if <TT>Codes</TT> is a list whose
elements are the character codes corresponding to the successive characters
of <TT>Constant</TT> (a number or an atom). However, there atoms are for
which <TT>name(Constant, Codes)</TT> is true, but which will not be
constructed if <TT>name/2</TT> is called with <TT>Constant</TT>
uninstantiated, e.g. the atom <TT>'1024'</TT>. For this reason the use of
<TT>name/2</TT> is discouraged and should be limited to compatibility
purposes. It is preferable to use atom_codes/2 (section <A HREF="#atom-chars/2">7.19.6</A>)
or number_chars/2 (section <A HREF="#number-atom/2">7.19.7</A>).<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Constant</TT> is a variable and <TT>Codes</TT> is a partial
list or a list with an element which is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Constant</TT> is neither a variable nor an atomic term</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atomic, Constant)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Constant</TT> is a variable and <TT>Codes</TT> is neither a list
nor a partial list</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(list, Codes)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Constant</TT> is a variable and an element <TT>E</TT> of the
list <TT>Codes</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Constant</TT> is a variable and an element <TT>E</TT> of the
list <TT>Codes</TT> is an integer but not a character code</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>representation_error(character_code)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc155"></A>
<H4 CLASS="subsubsection"><A NAME="htoc196">7.19.9</A> <TT>atom_hash/2</TT></H4>
<A NAME="atom-hash/2"></A>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
atom_hash(+atom, ?integer)<BR>
atom_hash(?atom, +integer)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>atom_hash(Atom, Hash)</TT> succeeds if <TT>Hash</TT> is the internal
key associated with <TT>Atom</TT> (an existing atom). The internal key of an
atom is a unique integer ≥ 0 and < to the <TT>max_atom</TT>
Prolog flag (section <A HREF="gprolog045.html#set-prolog-flag/2">7.22.1</A>).<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Atom</TT> and <TT>Hash</TT> are both variables</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></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> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Atom)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Hash</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Hash)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Hash</TT> is an integer < 0</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(not_less_than_zero, Hash)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc156"></A>
<H4 CLASS="subsubsection"><A NAME="htoc197">7.19.10</A> <TT>new_atom/3</TT>,
<TT>new_atom/2</TT>,
<TT>new_atom/1</TT></H4>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
new_atom(+atom, +integer, -atom)<BR>
new_atom(+atom, -atom)<BR>
new_atom(-atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>new_atom(Prefix, Hash, Atom)</TT> unifies <TT>Atom</TT> with a new atom
whose name begins with the characters of the name of <TT>Prefix</TT> and
whose internal key is <TT>Hash</TT> (section <A HREF="#atom-hash/2">7.19.9</A>). This predicate is
then a symbol generator. It is guaranteed that <TT>Atom</TT> does not exist
before the invocation of <TT>new_atom/3</TT>. The characters appended to
<TT>Prefix</TT> to form <TT>Atom</TT> are in: <TT>A</TT>-<TT>Z</TT> (capital
letter), <TT>a</TT>-<TT>z</TT> (small letter), <TT>0</TT>-<TT>9</TT>
(digit), <TT>#</TT>, <TT>$</TT>, <TT>&</TT>, <TT>_</TT>, <TT>@</TT>.<BR>
<BR>
<TT>new_atom/2</TT> is similar to <TT>new_atom/3</TT>, but the atom
generated can have any (free) internal key.<BR>
<BR>
<TT>new_atom/1</TT> is similar to <TT>new_atom(atom_, Atom)</TT>, i.e.
the generated atom begins with <TT>atom_</TT>.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Prefix</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Hash</TT> is a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>instantiation_error</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Prefix</TT> is neither a variable nor an atom</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Prefix)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Hash</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, Hash)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Hash</TT> is an integer < 0</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(not_less_than_zero, Hash)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Atom</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, Atom)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc157"></A>
<H4 CLASS="subsubsection"><A NAME="htoc198">7.19.11</A> <TT>current_atom/1</TT></H4>
<A NAME="current-atom/2"></A>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
current_atom(?atom)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>current_atom(Atom)</TT> succeeds if there exists an atom that unifies
with <TT>Atom</TT>. All atoms are found except those beginning with a
<TT>'$'</TT> (system atoms). This predicate is re-executable on
backtracking.<BR>
<BR>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></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> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Atom)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
<A NAME="toc158"></A>
<H4 CLASS="subsubsection"><A NAME="htoc199">7.19.12</A> <TT>atom_property/2</TT></H4>
<A NAME="atom-property/2"></A>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
atom_property(?atom, ?atom_property)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>atom_property(Atom, Property)</TT> succeeds if
<TT>current_atom(Atom)</TT> succeeds (section <A HREF="#current-atom/2">7.19.11</A>) and if
<TT>Property</TT> unifies with one of the properties of the atom. This
predicate is re-executable on backtracking.<BR>
<BR>
<B>Atom properties</B>:
<UL CLASS="itemize"><LI CLASS="li-itemize"><TT>length(Length)</TT>: <TT>Length</TT> is the length of the
name of the atom.<BR>
<BR>
<LI CLASS="li-itemize"><TT>hash(Hash)</TT>: <TT>Hash</TT> is the internal key of the
atom (section <A HREF="#atom-hash/2">7.19.9</A>).<BR>
<BR>
<LI CLASS="li-itemize"><TT>prefix_op</TT>: if there is a prefix operator currently defined
with this name.<BR>
<BR>
<LI CLASS="li-itemize"><TT>infix_op</TT>: if there is an infix operator currently defined
with this name.<BR>
<BR>
<LI CLASS="li-itemize"><TT>postfix_op</TT>: if there is a postfix operator currently defined
with this name.<BR>
<BR>
<LI CLASS="li-itemize"><TT>needs_quotes</TT>: if the atom must be quoted to be read later.<BR>
<BR>
<LI CLASS="li-itemize"><TT>needs_scan</TT>: if the atom must be scanned when output to be
read later (e.g. contains special characters that must be output with a
<TT>\</TT> escape sequence).</UL>
<B>Errors</B><BR>
<TABLE CELLSPACING=2 CELLPADDING=0>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></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> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(atom, Atom)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Property</TT> is neither a variable nor a n atom property term</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(atom_property, Property)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR>
<TR><TD VALIGN=top ALIGN=left><TT>Property</TT> = <TT>length(E)</TT> or <TT>hash(E)</TT> and
<TT>E</TT> is neither a variable nor an integer</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(integer, E)</TT></TD>
</TR>
<TR><TD BGCOLOR=black COLSPAN=3><TABLE BORDER=0 WIDTH="100%" CELLSPACING=0 CELLPADDING=1><TR><TD></TD></TR></TABLE></TD>
</TR></TABLE><BR>
<B>Portability</B><BR>
<BR>
GNU Prolog predicate.<BR>
<BR>
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