path: root/lib/stdlib/doc/src/epp.xml

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<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>1996</year><year>2016</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.

    </legalnotice>

    <title>epp</title>
    <prepared>Kenneth Lundin</prepared>
    <responsible>Kenneth Lundin</responsible>
    <docno>1</docno>
    <approved>Kenneth Lundin</approved>
    <checked></checked>
    <date>1997-01-31</date>
    <rev>B</rev>
    <file>epp.xml</file>
  </header>
  <module>epp</module>
  <modulesummary>An Erlang code preprocessor.</modulesummary>
  <description>
    <p>The Erlang code preprocessor includes functions that are used by the
      <seealso marker="compiler:compile"><c>compile</c></seealso>
      module to preprocess macros and include files before
      the parsing takes place.</p>

    <p>The Erlang source file <marker
      id="encoding"/><em>encoding</em> is selected by a
      comment in one of the first two lines of the source file. The
      first string matching the regular expression
      <c>coding\s*[:=]\s*([-a-zA-Z0-9])+</c> selects the encoding. If
      the matching string is not a valid encoding, it is ignored. The
      valid encodings are <c>Latin-1</c> and <c>UTF-8</c>, where the
      case of the characters can be chosen freely.</p>

    <p><em>Examples:</em></p>

    <pre>
%% coding: utf-8</pre>

    <pre>
%% For this file we have chosen encoding = Latin-1</pre>

    <pre>
%% -*- coding: latin-1 -*-</pre>
  </description>

  <datatypes>
    <datatype>
      <name name="macros"></name>
    </datatype>
    <datatype>
      <name name="epp_handle"></name>
      <desc><p>Handle to the <c>epp</c> server.</p></desc>
    </datatype>
    <datatype>
      <name name="source_encoding"></name>
    </datatype>
  </datatypes>

  <funcs>
    <func>
      <name name="close" arity="1"/>
      <fsummary>Close the preprocessing of the file associated with <c>Epp</c>.
      </fsummary>
      <desc>
        <p>Closes the preprocessing of a file.</p>
      </desc>
    </func>

    <func>
      <name name="default_encoding" arity="0" since="OTP R16B"/>
      <fsummary>Return the default encoding of Erlang source files.</fsummary>
      <desc>
        <p>Returns the default encoding of Erlang source files.</p>
      </desc>
    </func>

    <func>
      <name name="encoding_to_string" arity="1" since="OTP R16B"/>
      <fsummary>Return a string representation of an encoding.</fsummary>
      <desc>
        <p>Returns a string representation of an encoding. The string
          is recognized by
          <seealso marker="#read_encoding/1"><c>read_encoding/1,2</c></seealso>,
          <seealso marker="#read_encoding_from_binary/1">
          <c>read_encoding_from_binary/1,2</c></seealso>, and
          <seealso marker="#set_encoding/1"><c>set_encoding/1,2</c></seealso>
          as a valid encoding.</p>
      </desc>
    </func>

    <func>
      <name name="format_error" arity="1" since="OTP R14B03"/>
      <fsummary>Format an error descriptor.</fsummary>
      <desc>
        <p>Takes an <c><anno>ErrorDescriptor</anno></c> and returns
          a string that
          describes the error or warning. This function is usually
          called implicitly when processing an <c>ErrorInfo</c>
          structure (see section
          <seealso marker="#errorinfo">Error Information</seealso>).</p>
      </desc>
    </func>

    <func>
      <name name="open" arity="1" since="OTP 17.0"/>
      <fsummary>Open a file for preprocessing.</fsummary>
      <desc>
        <p>Opens a file for preprocessing.</p>
        <p>If you want to change the file name of the implicit -file()
          attributes inserted during preprocessing, you can do with
          <c>{source_name, <anno>SourceName</anno>}</c>. If unset it will
          default to the name of the opened file.</p>
        <p>If <c>extra</c> is specified in
          <c><anno>Options</anno></c>, the return value is
          <c>{ok, <anno>Epp</anno>, <anno>Extra</anno>}</c> instead
          of <c>{ok, <anno>Epp</anno>}</c>.</p>
      </desc>
    </func>

    <func>
      <name name="open" arity="2"/>
      <fsummary>Open a file for preprocessing.</fsummary>
      <desc>
        <p>Equivalent to
          <c>epp:open([{name, FileName}, {includes, IncludePath}])</c>.</p>
      </desc>
    </func>

    <func>
      <name name="open" arity="3"/>
      <fsummary>Open a file for preprocessing.</fsummary>
      <desc>
        <p>Equivalent to <c>epp:open([{name, FileName}, {includes, IncludePath},
          {macros, PredefMacros}])</c>.</p>
      </desc>
    </func>

    <func>
      <name name="parse_erl_form" arity="1"/>
      <fsummary>Return the next Erlang form from the opened Erlang source file.
      </fsummary>
      <type name="warning_info"/>
      <desc>
        <p>Returns the next Erlang form from the opened Erlang source file.
          Tuple <c>{eof, <anno>Line</anno>}</c> is returned at the end of the
          file. The first form corresponds to an implicit attribute
          <c>-file(File,1).</c>, where <c>File</c> is the file name.</p>
      </desc>
    </func>

    <func>
      <name name="parse_file" arity="2" since="OTP 17.0"/>
      <fsummary>Preprocess and parse an Erlang source file.</fsummary>
      <desc>
        <p>Preprocesses and parses an Erlang source file.
          Notice that tuple <c>{eof, <anno>Line</anno>}</c> returned at the
          end of the file is included as a "form".</p>
        <p>If you want to change the file name of the implicit -file()
          attributes inserted during preprocessing, you can do with
          <c>{source_name, <anno>SourceName</anno>}</c>. If unset it will
          default to the name of the opened file.</p>
        <p>If <c>extra</c> is specified in
         <c><anno>Options</anno></c>, the return value is
         <c>{ok, [<anno>Form</anno>], <anno>Extra</anno>}</c> instead
         of <c>{ok, [<anno>Form</anno>]}</c>.</p>
      </desc>
    </func>

    <func>
      <name name="parse_file" arity="3"/>
      <fsummary>Preprocess and parse an Erlang source file.</fsummary>
      <desc>
        <p>Equivalent to <c>epp:parse_file(FileName, [{includes, IncludePath},
          {macros, PredefMacros}])</c>.</p>
      </desc>
    </func>

    <func>
      <name name="read_encoding" arity="1" since="OTP R16B"/>
      <name name="read_encoding" arity="2" since="OTP R16B"/>
      <fsummary>Read the encoding from a file.</fsummary>
      <desc>
        <p>Read the <seealso marker="#encoding">encoding</seealso> from
          a file. Returns the read encoding, or <c>none</c> if no
          valid encoding is found.</p>
        <p>Option <c>in_comment_only</c> is <c>true</c> by
          default, which is correct for Erlang source files. If set to
          <c>false</c>, the encoding string does not necessarily have to
          occur in a comment.</p>
      </desc>
    </func>

    <func>
      <name name="read_encoding_from_binary" arity="1" since="OTP R16B"/>
      <name name="read_encoding_from_binary" arity="2" since="OTP R16B"/>
      <fsummary>Read the encoding from a binary.</fsummary>
      <desc>
        <p>Read the <seealso marker="#encoding">encoding</seealso> from
          a binary. Returns the read encoding, or <c>none</c> if no
          valid encoding is found.</p>
        <p>Option <c>in_comment_only</c> is <c>true</c> by
          default, which is correct for Erlang source files. If set to
          <c>false</c>, the encoding string does not necessarily have to
          occur in a comment.</p>
      </desc>
    </func>

    <func>
      <name name="set_encoding" arity="1" since="OTP R16B"/>
      <fsummary>Read and set the encoding of an I/O device.</fsummary>
      <desc>
        <p>Reads the <seealso marker="#encoding">encoding</seealso> from
          an I/O device and sets the encoding of the device
          accordingly. The position of the I/O device referenced by
          <c><anno>File</anno></c> is not affected. If no valid
          encoding can be read from the I/O device, the encoding of the
          I/O device is set to the default encoding.</p>
        <p>Returns the read encoding, or <c>none</c> if no valid
          encoding is found.</p>
      </desc>
    </func>

    <func>
      <name name="set_encoding" arity="2" since="OTP 17.0"/>
      <fsummary>Read and set the encoding of an I/O device.</fsummary>
      <desc>
        <p>Reads the <seealso marker="#encoding">encoding</seealso> from
          an I/O device and sets the encoding of the device
          accordingly. The position of the I/O device referenced by
          <c><anno>File</anno></c> is not affected. If no valid
          encoding can be read from the I/O device, the encoding of the
          I/O device is set to the
          <seealso marker="#encoding">encoding</seealso> specified by
          <c><anno>Default</anno></c>.</p>
        <p>Returns the read encoding, or <c>none</c> if no valid
          encoding is found.</p>
      </desc>
    </func>
  </funcs>

  <section>
    <title>Error Information</title>
    <marker id="errorinfo"/>
    <p><c>ErrorInfo</c> is the standard <c>ErrorInfo</c> structure that is
      returned from all I/O modules. The format is as follows:</p>
    <code type="none">
{ErrorLine, Module, ErrorDescriptor}</code>
    <p>A string describing the error is obtained with the following call:</p>
    <code type="none">
Module:format_error(ErrorDescriptor)</code>
  </section>

  <section>
    <title>See Also</title>
    <p><seealso marker="erl_parse"><c>erl_parse(3)</c></seealso></p>
  </section>
</erlref>