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

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<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>erl_parse</title>
    <prepared>Robert</prepared>
    <responsible>Bjarne D&auml;cker</responsible>
    <docno>1</docno>
    <approved>Bjarne D&auml;cker</approved>
    <checked></checked>
    <date>1997-01-24</date>
    <rev>B</rev>
    <file>erl_parse.xml</file>
  </header>
  <module>erl_parse</module>
  <modulesummary>The Erlang parser.</modulesummary>
  <description>
    <p>This module is the basic Erlang parser that converts tokens into
      the abstract form of either forms (that is, top-level constructs),
      expressions, or terms. The Abstract Format is described in the
      <seealso marker="erts:absform">ERTS User's Guide</seealso>.
      Notice that a token list must end with the <em>dot</em> token to be
      acceptable to the parse functions (see the <seealso marker="erl_scan">
      <c>erl_scan(3)</c></seealso>) module.</p>
  </description>

  <datatypes>
    <datatype>
      <name>abstract_clause()</name>
      <desc><p>Abstract form of an Erlang clause.</p>
      </desc>
    </datatype>
    <datatype>
      <name>abstract_expr()</name>
      <desc><p>Abstract form of an Erlang expression.</p>
      </desc>
    </datatype>
    <datatype>
      <name>abstract_form()</name>
      <desc><p>Abstract form of an Erlang form.</p>
      </desc>
    </datatype>
    <datatype>
      <name>abstract_type()</name>
      <desc><p>Abstract form of an Erlang type.</p>
      </desc>
    </datatype>
    <datatype>
      <name name="erl_parse_tree"></name>
    </datatype>
    <datatype>
      <name name="error_description"></name>
    </datatype>
    <datatype>
      <name name="error_info"></name>
    </datatype>
    <datatype>
      <name name="form_info"></name>
        <desc><p>Tuples <c>{error, error_info()}</c> and <c>{warning,
        error_info()}</c>, denoting syntactically incorrect forms and
        warnings, and <c>{eof, line()}</c>, denoting an end-of-stream
        encountered before a complete form had been parsed.</p>
      </desc>
    </datatype>
    <datatype>
      <name name="token"></name>
    </datatype>
  </datatypes>

  <funcs>
    <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 function is the inverse of
          <seealso marker="#normalise/1"><c>normalise/1</c></seealso>.</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"/>
      <fsummary>Convert an Erlang term into an abstract form.</fsummary>
      <type name="encoding_func"/>
      <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>Option <c><anno>Line</anno></c> is the line to be
          assigned to each node of <c><anno>AbsTerm</anno></c>.</p>
        <p>Option <c><anno>Encoding</anno></c> is used for
          selecting which integer lists to be considered
          as strings. The default is to use the encoding returned by
          function <seealso marker="epp#default_encoding/0">
          <c>epp:default_encoding/0</c></seealso>.
          Value <c>none</c> means that no integer lists are
          considered as strings. <c>encoding_func()</c> is
          called with one integer of a list at a time; if it
          returns <c>true</c> for every integer, the list is
          considered a string.</p>
      </desc>
    </func>

    <func>
      <name name="anno_from_term" arity="1"/>
      <fsummary>Return annotations as terms.</fsummary>
      <desc>
        <p>Assumes that <c><anno>Term</anno></c> is a term with the same
          structure as a <c>erl_parse</c> tree, but with terms,
          say <c>T</c>, where a <c>erl_parse</c> tree has collections
          of annotations. Returns a <c>erl_parse</c> tree where each
          term <c>T</c> is replaced by the value returned by
          <seealso marker="erl_anno#from_term/1">
          <c>erl_anno:from_term(T)</c></seealso>. The term
          <c><anno>Term</anno></c> 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 each collection of annotations
          <c>Anno</c> of the nodes of the <c>erl_parse</c> tree
          <c><anno>Abstr</anno></c> is replaced by the term
          returned by <seealso marker="erl_anno#to_term/1">
          <c>erl_anno:to_term(Anno)</c></seealso>. The
          <c>erl_parse</c> tree 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 <c>erl_parse</c> tree.
      </fsummary>
      <desc>
        <p>Updates an accumulator by applying <c><anno>Fun</anno></c> on
          each collection of annotations of the <c>erl_parse</c> tree
          <c><anno>Abstr</anno></c>. The first call to
          <c><anno>Fun</anno></c> has <c><anno>AccIn</anno></c> as
          argument, the returned accumulator
          <c><anno>AccOut</anno></c> is passed to the next call, and
          so on. The final value of the accumulator is returned. The
          <c>erl_parse</c> tree is traversed in a depth-first, left-to-right
          fashion.</p>
      </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
          that describes the error. This function is usually called
          implicitly when an <c>ErrorInfo</c> structure is processed
          (see section <seealso marker="#errorinfo">
          Error Information</seealso>).</p>
      </desc>
    </func>

    <func>
      <name name="map_anno" arity="2"/>
      <fsummary>Map a function over the annotations of an <c>erl_parse</c> tree.
      </fsummary>
      <desc>
        <p>Modifies the <c>erl_parse</c> tree <c><anno>Abstr</anno></c>
          by applying <c><anno>Fun</anno></c> on each collection of
          annotations of the nodes of the <c>erl_parse</c> tree. The
          <c>erl_parse</c> tree 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
        <c>erl_parse</c> tree.</fsummary>
      <desc>
        <p>Modifies the <c>erl_parse</c> tree <c><anno>Abstr</anno></c>
          by applying <c><anno>Fun</anno></c> on each collection of
          annotations of the nodes of the <c>erl_parse</c> tree, while
          at the same time updating an accumulator. The first call to
          <c><anno>Fun</anno></c> has <c><anno>AccIn</anno></c> as
          second argument, the returned accumulator
          <c><anno>AccOut</anno></c> is passed to the next call, and
          so on. The modified <c>erl_parse</c> tree and the
          final value of the accumulator are returned. The
          <c>erl_parse</c> tree 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>Assumes that <c><anno>Term</anno></c> is a term with the same
          structure as a <c>erl_parse</c> tree, but with <seealso
          marker="erl_anno#type-location">locations</seealso> where a
          <c>erl_parse</c> tree has collections of annotations.
          Returns a <c>erl_parse</c> tree where each location <c>L</c>
          is replaced by the value returned by <seealso
          marker="erl_anno#new/1"><c>erl_anno:new(L)</c></seealso>.
          The term <c><anno>Term</anno></c> is traversed in a
          depth-first, left-to-right fashion.</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 (that is, the
          term itself). This function is the inverse of
          <seealso marker="#abstract/1"><c>abstract/1</c></seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="parse_exprs" arity="1"/>
      <fsummary>Parse Erlang expressions.</fsummary>
      <desc>
        <p>Parses <c><anno>Tokens</anno></c> as if it was a list of expressions.
          Returns one of the following:</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_form" arity="1"/>
      <fsummary>Parse an Erlang form.</fsummary>
      <desc>
        <p>Parses <c><anno>Tokens</anno></c> as if it was a form. Returns one
          of the following:</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_term" arity="1"/>
      <fsummary>Parse an Erlang term.</fsummary>
      <desc>
        <p>Parses <c><anno>Tokens</anno></c> as if it was a term. Returns
          one of the following:</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, <anno>ErrorInfo</anno>}</c></tag>
          <item>
            <p>An error occurred.</p>
          </item>
        </taglist>
      </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>Generates a list of tokens representing the abstract
          form <c><anno>AbsTerm</anno></c> of an expression. Optionally,
          <c><anno>MoreTokens</anno></c> is appended.</p>
      </desc>
    </func>
  </funcs>

  <section>
    <marker id="errorinfo"/>
    <title>Error Information</title>
    <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_anno"><c>erl_anno(3)</c></seealso>,
       <seealso marker="erl_scan"><c>erl_scan(3)</c></seealso>,
       <seealso marker="io"><c>io(3)</c></seealso>,
        section <seealso marker="erts:absform">The Abstract Format</seealso>
        in the ERTS User's Guide</p>
  </section>
</erlref>