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Standard-Input-Representation.html

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  27. <a name="Standard-Input-Representation"></a>
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  29. Next:&nbsp;<a rel="next" accesskey="n" href="Standard-Output-Representation.html#Standard-Output-Representation">Standard Output Representation</a>,
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  34. 

  35. <h5 class="subsubsection">2.5.1.1 Standard Input Representation</h5>
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  36. 

  37. <p><a name="index-standard-input-179"></a>The representation for the standard input file used as the argument to
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  38. the function depends both on the file format and on the command line
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  39. options specified when the application is invoked. The
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  40. <a name="index-g_t_0040code_007bunparameterized_007d-command-line-option-180"></a><a name="index-g_t_0040code_007braw_002dmode_007d-command-line-option-181"></a><samp><span class="option">--unparameterized</span></samp> and <samp><span class="option">--raw-output</span></samp> options make no
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  41. difference to the input representation, and the <samp><span class="option">--line-map</span></samp>
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  42. and <samp><span class="option">--byte-transducer</span></samp> options are not relevant to this mode of
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  43. operation. That leaves four possible combined settings of the
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  44. <a name="index-g_t_0040code_007bchoice_002dof_002doutput_007d-command-line-option-182"></a><a name="index-g_t_0040code_007bforce_002dtext_002dinput_007d-command-line-option-183"></a><samp><span class="option">--choice-of-output</span></samp> and <samp><span class="option">--force-text-input</span></samp> options.  If
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  45. standard input conforms to the data file format specification <a href="File-Format.html#File-Format">File Format</a>,
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  46. the following effects are possible.
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  47. 

  48.      <ul>
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  49. <li>If neither <samp><span class="option">--choice-of-output</span></samp> nor
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  50. <samp><span class="option">--force-text-input</span></samp> is used, the argument to the function will
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  51. be given directly by the tree encoded in the data section of the
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  52. file. The preamble of the file will be ignored. 
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  53. <li>If the <samp><span class="option">--choice-of-output</span></samp> option is used
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  54. and the <samp><span class="option">--force-text-input</span></samp> option is not used, the argument to
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  55. the function will be a pair <code>(</code><var>preamble</var><code>,</code><var>contents</var><code>)</code>,
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  56. where <var>preamble</var> is a list of character strings taken from the
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  57. preamble of the file (with leading hashes stripped), and <var>contents</var>
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  58. is the tree represented in the data section of the file. 
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  59. <li>If the <samp><span class="option">--choice-of-output</span></samp> option is not used
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  60. and the <samp><span class="option">--force-text-input</span></samp> option is used, the argument to the
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  61. function will be the whole file as a list of character strings.  I.e.,
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  62. both the preamble and the data sections are included, hashes are not
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  63. stripped from the preamble, and the data section is not converted to the
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  64. tree it represents. 
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  65. <li>If the <samp><span class="option">--choice-of-output</span></samp> option is used
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  66. and the <samp><span class="option">--force-text-input</span></samp> option is also used, the argument to the
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  67. the function will be a pair <code>(nil,</code><var>contents</var><code>)</code>, where the
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  68. contents are the list of character strings as in the previous case. 
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  69. </ul>
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  70. 

  71.    <p><a name="index-file-format-184"></a>If standard input does not conform to the data file format specification
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  72. in <a href="File-Format.html#File-Format">File Format</a>, then it is assumed to be a text file. The
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  73. <samp><span class="option">--force-text-input</span></samp> option makes no difference, and there are
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  74. only two possible effects, depending on whether
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  75. <samp><span class="option">--choice-of-output</span></samp> is used. They correspond to the latter two
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  76. cases above, where <samp><span class="option">--force-text-input</span></samp> is used.
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  77. 

  78.    <p><a name="index-preamble-185"></a><a name="index-text-files-186"></a>The idea of the <samp><span class="option">--choice-of-output</span></samp> option is that it is used
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  79. only for applications that are smart enough to be aware of the
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  80. <code>(</code><var>preamble</var><code>,</code><var>contents</var><code>)</code> convention. A non-empty preamble
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  81. implies a data file whose contents could be any type, but an empty
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  82. preamble implies a text file whose contents can only be a list of
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  83. character strings. (In the case of a data file with no preamble, the
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  84. list of the empty string is used for the preamble to distinguish it from
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  85. a text file.)
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  86. 

  87.    <p>Dumb applications that never want to deal with anything but text files
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  88. should be invoked with <samp><span class="option">--force-text-input</span></samp>. Otherwise, they have
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  89. to be prepared for either text or data as arguments.
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  90. 

  91.    <p>The use of both options at once is unproductive as far as the input
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  92. format is concerned, but may be justified when the output is to be a
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  93. data file and the input is text only.
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