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  16. <H3 CLASS="subsection"><A NAME="htoc140">8.11</A>&#XA0;&#XA0;Constant term streams</H3><UL>
    17. 

  17. <LI><A HREF="gprolog035.html#toc107">Introduction</A>
    18. 

  18. </LI><LI><A HREF="gprolog035.html#toc108"><TT>open_input_atom_stream/2</TT>,
    19. 

  19. <TT>open_input_chars_stream/2</TT>,<BR>
    20. 

  20.  <TT>open_input_codes_stream/2</TT></A>
    21. 

  21. </LI><LI><A HREF="gprolog035.html#toc109"><TT>close_input_atom_stream/1</TT>,
    22. 

  22. <TT>close_input_chars_stream/1</TT>,<BR>
    23. 

  23.  <TT>close_input_codes_stream/1</TT></A>
    24. 

  24. </LI><LI><A HREF="gprolog035.html#toc110"><TT>open_output_atom_stream/1</TT>,
    25. 

  25. <TT>open_output_chars_stream/1</TT>,<BR>
    26. 

  26.  <TT>open_output_codes_stream/1</TT></A>
    27. 

  27. </LI><LI><A HREF="gprolog035.html#toc111"><TT>close_output_atom_stream/2</TT>,
    28. 

  28. <TT>close_output_chars_stream/2</TT>,<BR>
    29. 

  29.  <TT>close_output_codes_stream/2</TT></A>
    30. 

  30. </LI></UL>
    31. 

  31. <P>
    32. 

  32. <A NAME="Constant-term-streams"></A></P><H4 CLASS="subsubsection"><A NAME="toc107"></A><A NAME="htoc141">8.11.1</A>&#XA0;&#XA0;Introduction</H4><P>
    33. 

  33. <A NAME="Introduction:(Constant-term-streams)"></A>
    34. 

  34. Constant term streams allow the user to consider a constant term (atom,
    35. 

  35. character list or character code list) as a source/sink by associating to
    36. 

  36. them a stream. Reading from a constant term stream will deliver the
    37. 

  37. characters of the constant term as if they had been read from a standard
    38. 

  38. file. Characters written on a constant term stream are stored to form the
    39. 

  39. final constant term when the stream is closed. The built-in predicates
    40. 

  40. described in this section allow the user to open and close a constant term
    41. 

  41. stream for input or output. However, very often, a constant term stream is
    42. 

  42. created to be only read or written once and then closed. To avoid the
    43. 

  43. creation and the destruction of such a stream, GNU Prolog offers several
    44. 

  44. built-in predicates to perform single input/output from/to constant terms
    45. 

  45. (section&#XA0;<A HREF="gprolog039.html#Input/output-from/to-constant-terms">8.15</A>).</P><H4 CLASS="subsubsection"><A NAME="toc108"></A><A NAME="htoc142">8.11.2</A>&#XA0;&#XA0;<TT>open_input_atom_stream/2</TT>,
    46. 

  46. <TT>open_input_chars_stream/2</TT>,<BR>
    47. 

  47.  <TT>open_input_codes_stream/2</TT></H4><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
    48. 

  48. </DT><DD CLASS="dd-list"><TT>
    49. 

  49. open_input_atom_stream(+atom, -stream)<BR>
    50. 

  50. open_input_chars_stream(+character_list, -stream)<BR>
    51. 

  51. open_input_codes_stream(+character_code_list, -stream)</TT></DD></DL><P><B>Description</B></P><P><TT>open_input_atom_stream(Atom, Stream)</TT> unifies <TT>Stream</TT>
    52. 

  52. with the stream-term which is associated with a new input text-stream whose
    53. 

  53. data are the characters of <TT>Atom</TT>.</P><P><TT>open_input_chars_stream(Chars, Stream)</TT> is similar to
    54. 

  54. <TT>open_input_atom_stream/2</TT> except that data are the content of the
    55. 

  55. character list <TT>Chars</TT>.</P><P><TT>open_input_codes_stream(Codes, Stream)</TT> is similar to
    56. 

  56. <TT>open_input_atom_stream/2</TT> except that data are the content of the
    57. 

  57. character code list <TT>Codes</TT>.</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    58. 

  58. <TR><TD VALIGN=top ALIGN=left>
    59. 

  59. <TT>Stream</TT> is not a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(variable, Stream)</TT></TD></TR>
    60. 

  60. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    61. 

  61. <TR><TD VALIGN=top ALIGN=left>
    62. 

  62. <TT>Atom</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>
    63. 

  63. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    64. 

  64. <TR><TD VALIGN=top ALIGN=left>
    65. 

  65. <TT>Chars</TT> is a partial list or a list with an element
    66. 

  66. <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>
    67. 

  67. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    68. 

  68. <TR><TD VALIGN=top ALIGN=left>
    69. 

  69. <TT>Codes</TT> is a partial list or a list with an element
    70. 

  70. <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>
    71. 

  71. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    72. 

  72. <TR><TD VALIGN=top ALIGN=left>
    73. 

  73. <TT>Atom</TT> is neither a variable nor a 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>
    74. 

  74. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    75. 

  75. <TR><TD VALIGN=top ALIGN=left>
    76. 

  76. <TT>Chars</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, Chars)</TT></TD></TR>
    77. 

  77. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    78. 

  78. <TR><TD VALIGN=top ALIGN=left>
    79. 

  79. <TT>Codes</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, Codes)</TT></TD></TR>
    80. 

  80. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    81. 

  81. <TR><TD VALIGN=top ALIGN=left>
    82. 

  82. an element <TT>E</TT> of the <TT>Chars</TT> list is neither a
    83. 

  83. variable nor a character</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(character, E)</TT></TD></TR>
    84. 

  84. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    85. 

  85. <TR><TD VALIGN=top ALIGN=left>
    86. 

  86. an element <TT>E</TT> of the <TT>Codes</TT> list is neither a
    87. 

  87. variable nor an integer</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(integer, E)</TT></TD></TR>
    88. 

  88. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    89. 

  89. <TR><TD VALIGN=top ALIGN=left>
    90. 

  90. an element <TT>E</TT> of the <TT>Codes</TT> list is an integer but
    91. 

  91. not a character code</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>representation_error(character_code)</TT></TD></TR>
    92. 

  92. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    93. 

  93. </TABLE><P><B>Portability</B></P><P>GNU Prolog predicates.</P><H4 CLASS="subsubsection"><A NAME="toc109"></A><A NAME="htoc143">8.11.3</A>&#XA0;&#XA0;<TT>close_input_atom_stream/1</TT>,
    94. 

  94. <TT>close_input_chars_stream/1</TT>,<BR>
    95. 

  95.  <TT>close_input_codes_stream/1</TT></H4><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
    96. 

  96. </DT><DD CLASS="dd-list"><TT>
    97. 

  97. close_input_atom_stream(+stream_or_alias)<BR>
    98. 

  98. close_input_chars_stream(+stream_or_alias)<BR>
    99. 

  99. close_input_codes_stream(+stream_or_alias)</TT></DD></DL><P><B>Description</B></P><P><TT>close_input_atom_stream(SorA)</TT> closes the constant term stream
    100. 

  100. associated with the stream-term or alias <TT>SorA</TT>. <TT>SorA</TT> must a
    101. 

  101. stream open with <TT>open_input_atom_stream/2</TT>
    102. 

  102. (section&#XA0;<A HREF="#Introduction:(Constant-term-streams)">8.11.1</A>).</P><P><TT>close_input_chars_stream(SorA)</TT> acts similarly for a character
    103. 

  103. list stream.</P><P><TT>close_input_codes_stream(SorA)</TT> acts similarly for a character
    104. 

  104. code list stream.</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    105. 

  105. <TR><TD VALIGN=top ALIGN=left>
    106. 

  106. <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>
    107. 

  107. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    108. 

  108. <TR><TD VALIGN=top ALIGN=left>
    109. 

  109. <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>
    110. 

  110. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    111. 

  111. <TR><TD VALIGN=top ALIGN=left>
    112. 

  112. <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>
    113. 

  113. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    114. 

  114. <TR><TD VALIGN=top ALIGN=left>
    115. 

  115. <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(close, stream, SorA)</TT></TD></TR>
    116. 

  116. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    117. 

  117. <TR><TD VALIGN=top ALIGN=left>
    118. 

  118. <TT>SorA</TT> is a stream-term or alias but does not refer to a
    119. 

  119. constant term stream.</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(term_stream_or_alias, SorA)</TT></TD></TR>
    120. 

  120. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    121. 

  121. </TABLE><P><B>Portability</B></P><P>GNU Prolog predicates.</P><H4 CLASS="subsubsection"><A NAME="toc110"></A><A NAME="htoc144">8.11.4</A>&#XA0;&#XA0;<TT>open_output_atom_stream/1</TT>,
    122. 

  122. <TT>open_output_chars_stream/1</TT>,<BR>
    123. 

  123.  <TT>open_output_codes_stream/1</TT></H4><P>
    124. 

  124. <A NAME="open-output-atom-stream/1"></A>
    125. 

  125. 

  126. 

  127. </P><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
    128. 

  128. </DT><DD CLASS="dd-list"><TT>
    129. 

  129. open_output_atom_stream(-stream)<BR>
    130. 

  130. open_output_chars_stream(-stream)<BR>
    131. 

  131. open_output_codes_stream(-stream)</TT></DD></DL><P><B>Description</B></P><P><TT>open_output_atom_stream(Stream)</TT> unifies <TT>Stream</TT> with the
    132. 

  132. stream-term which is associated with a new output text-stream. All characters
    133. 

  133. written to this stream are collected and will be returned as an atom when
    134. 

  134. the stream is closed by <TT>close_output_atom_stream/2</TT>
    135. 

  135. (section&#XA0;<A HREF="#close-output-atom-stream/2">8.11.5</A>).</P><P><TT>open_output_chars_stream(Stream)</TT> is similar to
    136. 

  136. <TT>open_output_atom_stream/1</TT> except that the result will be a
    137. 

  137. character list.</P><P><TT>open_output_codes_stream(Stream)</TT> is similar to
    138. 

  138. <TT>open_output_atom_stream/1</TT> except that the result will be a
    139. 

  139. character code list.</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    140. 

  140. <TR><TD VALIGN=top ALIGN=left>
    141. 

  141. <TT>Stream</TT> is not a variable</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(variable, Stream)</TT></TD></TR>
    142. 

  142. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    143. 

  143. </TABLE><P><B>Portability</B></P><P>GNU Prolog predicates.</P><H4 CLASS="subsubsection"><A NAME="toc111"></A><A NAME="htoc145">8.11.5</A>&#XA0;&#XA0;<TT>close_output_atom_stream/2</TT>,
    144. 

  144. <TT>close_output_chars_stream/2</TT>,<BR>
    145. 

  145.  <TT>close_output_codes_stream/2</TT></H4><P>
    146. 

  146. <A NAME="close-output-atom-stream/2"></A>
    147. 

  147. 

  148. 

  149. </P><P><B>Templates</B></P><DL CLASS="list"><DT CLASS="dt-list">
    150. 

  150. </DT><DD CLASS="dd-list"><TT>
    151. 

  151. close_output_atom_stream(+stream_or_alias, ?atom)<BR>
    152. 

  152. close_output_chars_stream(+stream_or_alias, ?character_list)<BR>
    153. 

  153. close_output_codes_stream(+stream_or_alias, ?character_code_list)</TT></DD></DL><P><B>Description</B></P><P><TT>close_output_atom_stream(SorA, Atom)</TT> closes the constant term
    154. 

  154. stream associated with the stream-term or alias <TT>SorA</TT>. <TT>SorA</TT> must
    155. 

  155. be associated with a stream open with <TT>open_output_atom_stream/1</TT>
    156. 

  156. (section&#XA0;<A HREF="#open-output-atom-stream/1">8.11.4</A>). <TT>Atom</TT> is unified with an atom
    157. 

  157. formed with all characters written on the stream.</P><P><TT>close_output_chars_stream(SorA, Chars)</TT> acts similarly for a
    158. 

  158. character list stream.</P><P><TT>close_output_codes_stream(SorA, Codes)</TT> acts similarly for a
    159. 

  159. character code list stream.</P><P><B>Errors</B></P><TABLE CELLSPACING=6 CELLPADDING=0><TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    160. 

  160. <TR><TD VALIGN=top ALIGN=left>
    161. 

  161. <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>
    162. 

  162. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    163. 

  163. <TR><TD VALIGN=top ALIGN=left>
    164. 

  164. <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>
    165. 

  165. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    166. 

  166. <TR><TD VALIGN=top ALIGN=left>
    167. 

  167. <TT>Chars</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, Chars)</TT></TD></TR>
    168. 

  168. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    169. 

  169. <TR><TD VALIGN=top ALIGN=left>
    170. 

  170. <TT>Codes</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, Codes)</TT></TD></TR>
    171. 

  171. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    172. 

  172. <TR><TD VALIGN=top ALIGN=left>
    173. 

  173. an element <TT>E</TT> of the <TT>Chars</TT> list is neither a
    174. 

  174. variable nor a character</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(character, E)</TT></TD></TR>
    175. 

  175. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    176. 

  176. <TR><TD VALIGN=top ALIGN=left>
    177. 

  177. an element <TT>E</TT> of the <TT>Codes</TT> list is neither a
    178. 

  178. variable nor an integer</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>type_error(integer, E)</TT></TD></TR>
    179. 

  179. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    180. 

  180. <TR><TD VALIGN=top ALIGN=left>
    181. 

  181. an element <TT>E</TT> of the <TT>Codes</TT> list is an integer but
    182. 

  182. not a character code</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>representation_error(character_code)</TT></TD></TR>
    183. 

  183. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    184. 

  184. <TR><TD VALIGN=top ALIGN=left>
    185. 

  185. <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>
    186. 

  186. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    187. 

  187. <TR><TD VALIGN=top ALIGN=left>
    188. 

  188. <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>
    189. 

  189. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    190. 

  190. <TR><TD VALIGN=top ALIGN=left>
    191. 

  191. <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(close, stream, SorA)</TT></TD></TR>
    192. 

  192. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    193. 

  193. <TR><TD VALIGN=top ALIGN=left>
    194. 

  194. <TT>SorA</TT> is a stream-term or alias but does not refer to a
    195. 

  195. constant term stream</TD><TD VALIGN=top ALIGN=center NOWRAP>&#XA0;&#XA0;</TD><TD VALIGN=top ALIGN=left><TT>domain_error(term_stream_or_alias, SorA)</TT></TD></TR>
    196. 

  196. <TR><TD CLASS="hbar" COLSPAN=3></TD></TR>
    197. 

  197. </TABLE><P><B>Portability</B></P><P>GNU Prolog predicates.</P>
    198. 

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    199. 

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    200. 

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    201. 

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