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

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<erlref>
  <header>
    <copyright>
      <year>1996</year><year>2015</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
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    </legalnotice>

    <title>erl_parse</title>
    <prepared>Robert</prepared>
    <responsible>Bjarne D&auml;cker</responsible>
    <docno>1</docno>
    <approved>Bjarne D&auml;cker</approved>
    <checked></checked>
    <date>97-01-24</date>
    <rev>B</rev>
    <file>erl_parse.sgml</file>
  </header>
  <module>erl_parse</module>
  <modulesummary>The Erlang Parser</modulesummary>
  <description>
    <p>This module is the basic Erlang parser which converts tokens into
      the abstract form of either forms (i.e., top-level constructs),
      expressions, or terms. The Abstract Format is described in the
      <seealso marker="erts:absform">ERTS User's Guide</seealso>.
      Note that a token list must end with the <em>dot</em> token in order
      to be acceptable to the parse functions (see <seealso marker="erl_scan">erl_scan(3)</seealso>).</p>
  </description>
  <datatypes>
    <datatype>
      <name name="abstract_clause"></name>
      <desc><p>Parse tree for Erlang clause.</p>
      </desc>
    </datatype>
    <datatype>
      <name name="abstract_expr"></name>
      <desc><p>Parse tree for Erlang expression.</p>
      </desc>
    </datatype>
    <datatype>
      <name name="abstract_form"></name>
      <desc><p>Parse tree for Erlang form.</p>
      </desc>
    </datatype>
    <datatype>
      <name name="error_description"></name>
    </datatype>
    <datatype>
      <name name="error_info"></name>
    </datatype>
    <datatype>
      <name name="token"></name>
    </datatype>
  </datatypes>
  <funcs>
    <func>
      <name name="parse_form" arity="1"/>
      <fsummary>Parse an Erlang form</fsummary>
      <desc>
        <p>This function parses <c><anno>Tokens</anno></c> as if it were
          a form. It returns:</p>
        <taglist>
          <tag><c>{ok, <anno>AbsForm</anno>}</c></tag>
          <item>
            <p>The parsing was successful. <c><anno>AbsForm</anno></c> is the
              abstract form of the parsed form.</p>
          </item>
          <tag><c>{error, <anno>ErrorInfo</anno>}</c></tag>
          <item>
            <p>An error occurred.</p>
          </item>
        </taglist>
      </desc>
    </func>
    <func>
      <name name="parse_exprs" arity="1"/>
      <fsummary>Parse Erlang expressions</fsummary>
      <desc>
        <p>This function parses <c><anno>Tokens</anno></c> as if it were
          a list of expressions. It returns:</p>
        <taglist>
          <tag><c>{ok, <anno>ExprList</anno>}</c></tag>
          <item>
            <p>The parsing was successful. <c><anno>ExprList</anno></c> is a
              list of the abstract forms of the parsed expressions.</p>
          </item>
          <tag><c>{error, <anno>ErrorInfo</anno>}</c></tag>
          <item>
            <p>An error occurred.</p>
          </item>
        </taglist>
      </desc>
    </func>
    <func>
      <name name="parse_term" arity="1"/>
      <fsummary>Parse an Erlang term</fsummary>
      <desc>
        <p>This function parses <c><anno>Tokens</anno></c> as if it were
          a term. It returns:</p>
        <taglist>
          <tag><c>{ok, <anno>Term</anno>}</c></tag>
          <item>
            <p>The parsing was successful. <c><anno>Term</anno></c> is
              the Erlang term corresponding to the token list.</p>
          </item>
          <tag><c>{error, ErrorInfo}</c></tag>
          <item>
            <p>An error occurred.</p>
          </item>
        </taglist>
      </desc>
    </func>
    <func>
      <name>format_error(ErrorDescriptor) -> Chars</name>
      <fsummary>Format an error descriptor</fsummary>
      <type>
        <v>ErrorDescriptor = <seealso
          marker="#type-error_info">error_description()</seealso></v>
        <v>Chars = [char() | Chars]</v>
      </type>
      <desc>
        <p>Uses an <c>ErrorDescriptor</c> and returns a string
          which describes the error. This function is usually called
          implicitly when an <c>ErrorInfo</c> structure is processed
          (see below).</p>
      </desc>
    </func>
    <func>
      <name name="tokens" arity="1"/>
      <name name="tokens" arity="2"/>
      <fsummary>Generate a list of tokens for an expression</fsummary>
      <desc>
        <p>This function generates a list of tokens representing the abstract
          form <c><anno>AbsTerm</anno></c> of an expression. Optionally, it
          appends <c><anno>MoreTokens</anno></c>.</p>
      </desc>
    </func>
    <func>
      <name name="normalise" arity="1"/>
      <fsummary>Convert abstract form to an Erlang term</fsummary>
      <desc>
        <p>Converts the abstract form <c><anno>AbsTerm</anno></c> of a
          term into a
          conventional Erlang data structure (i.e., the term itself).
          This is the inverse of <c>abstract/1</c>.</p>
      </desc>
    </func>
    <func>
      <name name="abstract" arity="1"/>
      <fsummary>Convert an Erlang term into an abstract form</fsummary>
      <desc>
        <p>Converts the Erlang data structure <c><anno>Data</anno></c> into an
          abstract form of type <c><anno>AbsTerm</anno></c>.
          This is the inverse of <c>normalise/1</c>.</p>
        <p><c>erl_parse:abstract(T)</c> is equivalent to
          <c>erl_parse:abstract(T, 0)</c>.</p>
      </desc>
    </func>
    <func>
      <name name="abstract" arity="2"/>
      <type name="encoding_func"/>
      <fsummary>Convert an Erlang term into an abstract form</fsummary>
      <desc>
        <p>Converts the Erlang data structure <c><anno>Data</anno></c> into an
          abstract form of type <c><anno>AbsTerm</anno></c>.</p>
        <p>The <c><anno>Line</anno></c> option is the line that will
          be assigned to each node of the abstract form.</p>
        <p>The <c><anno>Encoding</anno></c> option is used for
          selecting which integer lists will be considered
          as strings. The default is to use the encoding returned by
          <seealso marker="epp#default_encoding/0">
          <c>epp:default_encoding/0</c></seealso>.
          The value <c>none</c> means that no integer lists will be
          considered as strings. The <c>encoding_func()</c> will be
          called with one integer of a list at a time, and if it
          returns <c>true</c> for every integer the list will be
          considered a string.</p>
      </desc>
    </func>
    <func>
      <name name="map_anno" arity="2"/>
      <fsummary>
        Map a function over the annotations of an abstract form
      </fsummary>
      <desc>
        <p>Modifies the abstract form <anno>Abstr</anno> by applying
          <anno>Fun</anno> on every collection of annotations of the
          abstract form. The abstract form is traversed in a
          depth-first, left-to-right, fashion.
        </p>
      </desc>
    </func>
    <func>
      <name name="fold_anno" arity="3"/>
      <fsummary>
        Fold a function over the annotations of an abstract form
      </fsummary>
      <desc>
        <p>Updates an accumulator by applying <anno>Fun</anno> on
          every collection of annotations of the abstract form
          <anno>Abstr</anno>. The first call to <anno>Fun</anno> has
          <anno>AccIn</anno> as argument, and the returned accumulator
          <anno>AccOut</anno> is passed to the next call, and so on.
          The final value of the accumulator is returned. The abstract
          form is traversed in a depth-first, left-to-right, fashion.
        </p>
      </desc>
    </func>
    <func>
      <name name="mapfold_anno" arity="3"/>
      <fsummary>
        Map and fold a function over the annotations of an abstract form
      </fsummary>
      <desc>
        <p>Modifies the abstract form <anno>Abstr</anno> by applying
          <anno>Fun</anno> on every collection of annotations of the
          abstract form, while at the same time updating an
          accumulator. The first call to <anno>Fun</anno> has
          <anno>AccIn</anno> as second argument, and the returned
          accumulator <anno>AccOut</anno> is passed to the next call,
          and so on. The modified abstract form as well as the the
          final value of the accumulator is returned. The abstract
          form is traversed in a depth-first, left-to-right, fashion.
        </p>
      </desc>
    </func>
    <func>
      <name name="new_anno" arity="1"/>
      <fsummary>
        Create new annotations
      </fsummary>
      <desc>
        <p>Creates an abstract form from a term which has the same
          structure as an abstract form, but <seealso
          marker="erl_anno#type-location">locations</seealso> where the
          abstract form has annotations. For each location, <seealso
          marker="erl_anno#new/1"><c>erl_anno:new/1</c></seealso> is
          called, and the annotations replace the location.
        </p>
      </desc>
    </func>
    <func>
      <name name="anno_from_term" arity="1"/>
      <fsummary>
        Return annotations as terms
      </fsummary>
      <desc>
        <p>Assumes that <anno>Term</anno> is a term with the same
          structure as an abstract form, but with terms, T say, on
          those places where an abstract form has annotations. Returns
          an abstract form where every term T has been replaced by the
          value returned by calling <c>erl_anno:from_term(T)</c>. The
          term <anno>Term</anno> is traversed in a depth-first,
          left-to-right, fashion.
        </p>
      </desc>
    </func>
    <func>
      <name name="anno_to_term" arity="1"/>
      <fsummary>
        Return the representation of annotations
      </fsummary>
      <desc>
        <p>Returns a term where every collection of annotations Anno of
          <anno>Abstr</anno> has been replaced by the term returned by
          calling <c>erl_anno:to_term(Anno)</c>. The abstract form is
          traversed in a depth-first, left-to-right, fashion.
        </p>
      </desc>
    </func>
  </funcs>

  <section>
    <title>Error Information</title>
    <p>The <c>ErrorInfo</c> mentioned above is the standard
      <c>ErrorInfo</c> structure which is returned from all IO
      modules. It has the format:
      </p>
    <code type="none">
    {ErrorLine, Module, ErrorDescriptor}    </code>
    <p>A string which describes 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="io">io(3)</seealso>,
       <seealso marker="erl_anno">erl_anno(3)</seealso>,
       <seealso marker="erl_scan">erl_scan(3)</seealso>,
       <seealso marker="erts:absform">ERTS User's Guide</seealso></p>
  </section>
</erlref>