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Constant term streams
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<H3 CLASS="subsection"><A NAME="htoc133">7.11</A> Constant term streams</H3><UL>
<LI><A HREF="gprolog034.html#toc101">Introduction</A>
<LI><A HREF="gprolog034.html#toc102"><TT>open_input_atom_stream/2</TT>,
<TT>open_input_chars_stream/2</TT>,<BR>
<TT>open_input_codes_stream/2</TT></A>
<LI><A HREF="gprolog034.html#toc103"><TT>close_input_atom_stream/1</TT>,
<TT>close_input_chars_stream/1</TT>,<BR>
<TT>close_input_codes_stream/1</TT></A>
<LI><A HREF="gprolog034.html#toc104"><TT>open_output_atom_stream/1</TT>,
<TT>open_output_chars_stream/1</TT>,<BR>
<TT>open_output_codes_stream/1</TT></A>
<LI><A HREF="gprolog034.html#toc105"><TT>close_output_atom_stream/2</TT>,
<TT>close_output_chars_stream/2</TT>,<BR>
<TT>close_output_codes_stream/2</TT></A>
</UL>
<A NAME="Constant-term-streams"></A>
<A NAME="toc101"></A>
<H4 CLASS="subsubsection"><A NAME="htoc134">7.11.1</A> Introduction</H4>
<A NAME="Introduction:(Constant-term-streams)"></A>
Constant term streams allow the user to consider a constant term (atom,
character list or character code list) as a source/sink by associating to
them a stream. Reading from a constant term stream will deliver the
characters of the constant term as if they had been read from a standard
file. Characters written on a constant term stream are stored to form the
final constant term when the stream is closed. The built-in predicates
described in this section allow the user to open and close a constant term
stream for input or output. However, very often, a constant term stream is
created to be only read or written once and then closed. To avoid the
creation and the destruction of such a stream, GNU Prolog offers several
built-in predicates to perform single input/output from/to constant terms
(section <A HREF="gprolog038.html#Input/output-from/to-constant-terms">7.15</A>).<BR>
<BR>
<A NAME="toc102"></A>
<H4 CLASS="subsubsection"><A NAME="htoc135">7.11.2</A> <TT>open_input_atom_stream/2</TT>,
<TT>open_input_chars_stream/2</TT>,<BR>
<TT>open_input_codes_stream/2</TT></H4>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
open_input_atom_stream(+atom, -stream)<BR>
open_input_chars_stream(+character_list, -stream)<BR>
open_input_codes_stream(+character_code_list, -stream)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>open_input_atom_stream(Atom, Stream)</TT> unifies <TT>Stream</TT>
with the stream-term which is associated with a new input text-stream whose
data are the characters of <TT>Atom</TT>.<BR>
<BR>
<TT>open_input_chars_stream(Chars, Stream)</TT> is similar to
<TT>open_input_atom_stream/2</TT> except that data are the content of the
character list <TT>Chars</TT>.<BR>
<BR>
<TT>open_input_codes_stream(Codes, Stream)</TT> is similar to
<TT>open_input_atom_stream/2</TT> except that data are the content of the
character code list <TT>Codes</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>Stream</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, Stream)</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</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>Chars</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> </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>Codes</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> </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 a 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 partial list nor a 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 partial list nor a 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>an element <TT>E</TT> of the <TT>Chars</TT> list is neither a
variable nor a character</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>an element <TT>E</TT> of the <TT>Codes</TT> list 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>an element <TT>E</TT> of the <TT>Codes</TT> list 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 predicates.<BR>
<BR>
<A NAME="toc103"></A>
<H4 CLASS="subsubsection"><A NAME="htoc136">7.11.3</A> <TT>close_input_atom_stream/1</TT>,
<TT>close_input_chars_stream/1</TT>,<BR>
<TT>close_input_codes_stream/1</TT></H4>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
close_input_atom_stream(+stream_or_alias)<BR>
close_input_chars_stream(+stream_or_alias)<BR>
close_input_codes_stream(+stream_or_alias)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>close_input_atom_stream(SorA)</TT> closes the constant term stream
associated with the stream-term or alias <TT>SorA</TT>. <TT>SorA</TT> must a
stream open with <TT>open_input_atom_stream/2</TT>
(section <A HREF="#Introduction:(Constant-term-streams)">7.11.1</A>).<BR>
<BR>
<TT>close_input_chars_stream(SorA)</TT> acts similarly for a character
list stream.<BR>
<BR>
<TT>close_input_codes_stream(SorA)</TT> acts similarly for a character
code list stream.<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>SorA</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>SorA</TT> is neither a variable nor a stream-term or alias</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(stream_or_alias, SorA)</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>SorA</TT> is not associated with an open stream</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>existence_error(stream, SorA)</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>SorA</TT> is an output stream</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>permission_error(close, stream, SorA)</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>SorA</TT> is a stream-term or alias but does not refer to a
constant term stream.</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(term_stream_or_alias, SorA)</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 predicates.<BR>
<BR>
<A NAME="toc104"></A>
<H4 CLASS="subsubsection"><A NAME="htoc137">7.11.4</A> <TT>open_output_atom_stream/1</TT>,
<TT>open_output_chars_stream/1</TT>,<BR>
<TT>open_output_codes_stream/1</TT></H4>
<A NAME="open-output-atom-stream/1"></A>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
open_output_atom_stream(-stream)<BR>
open_output_chars_stream(-stream)<BR>
open_output_codes_stream(-stream)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>open_output_atom_stream(Stream)</TT> unifies <TT>Stream</TT> with the
stream-term which is associated with a new output text-stream. All characters
written to this stream are collected and will be returned as an atom when
the stream is closed by <TT>close_ouput_atom_stream/2</TT>
(section <A HREF="#close-output-atom-stream/2">7.11.5</A>).<BR>
<BR>
<TT>open_output_chars_stream(Stream)</TT> is similar to
<TT>open_output_atom_stream/1</TT> except that the result will be a
character list.<BR>
<BR>
<TT>open_output_codes_stream(Stream)</TT> is similar to
<TT>open_output_atom_stream/1</TT> except that the result will be a
character code list.<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>Stream</TT> is not a variable</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>type_error(variable, Stream)</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 predicates.<BR>
<BR>
<A NAME="toc105"></A>
<H4 CLASS="subsubsection"><A NAME="htoc138">7.11.5</A> <TT>close_output_atom_stream/2</TT>,
<TT>close_output_chars_stream/2</TT>,<BR>
<TT>close_output_codes_stream/2</TT></H4>
<A NAME="close-output-atom-stream/2"></A>
<B>Templates</B>
<DL CLASS="list" COMPACT="compact"><DT CLASS="dt-list"><DD CLASS="dd-list"><TT>
close_output_atom_stream(+stream_or_alias, ?atom)<BR>
close_output_chars_stream(+stream_or_alias, ?character_list)<BR>
close_output_codes_stream(+stream_or_alias, ?character_code_list)</TT></DL>
<B>Description</B><BR>
<BR>
<TT>close_output_atom_stream(SorA, Atom)</TT> closes the constant term
stream associated with the stream-term or alias <TT>SorA</TT>. <TT>SorA</TT> must
be associated with a stream open with <TT>open_output_atom_stream/1</TT>
(section <A HREF="#open-output-atom-stream/1">7.11.4</A>). <TT>Atom</TT> is unified with an atom
formed with all characters written on the stream.<BR>
<BR>
<TT>close_output_chars_stream(SorA, Chars)</TT> acts similarly for a
character list stream.<BR>
<BR>
<TT>close_output_codes_stream(SorA, Codes)</TT> acts similarly for a
character code list stream.<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>SorA</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>Chars</TT> is neither a partial list nor a 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 partial list nor a 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>SorA</TT> is neither a variable nor a stream-term or alias</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(stream_or_alias, SorA)</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>SorA</TT> is not associated with an open stream</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>existence_error(stream, SorA)</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>SorA</TT> is an input stream</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>permission_error(close, stream, SorA)</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>SorA</TT> is a stream-term or alias but does not refer to a
constant term stream</TD>
<TD VALIGN=top ALIGN=center NOWRAP> </TD>
<TD VALIGN=top ALIGN=left><TT>domain_error(term_stream_or_alias, SorA)</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 predicates.<BR>
<BR>
<HR SIZE=2>
Copyright (C) 1999-2007 Daniel Diaz
<BR>
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