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>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>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="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"/>
      <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>The <c><anno>Line</anno></c> option is the line that will
          be assigned to each node of <c><anno>AbsTerm</anno></c>.</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 a <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="fold_anno" arity="3"/>
      <fsummary>
        Fold a function over the annotations of a <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, and 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 name="mapfold_anno" arity="3"/>
      <fsummary>
        Map and fold a function over the annotations of a
        <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, and the returned accumulator
	  <c><anno>AccOut</anno></c> is passed to the next call, and
	  so on. The modified <c>erl_parse</c> tree as well as the 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>
          has been 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="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,
          <c>T</c> say, where a <c>erl_parse</c> tree has collections
          of annotations. Returns a <c>erl_parse</c> tree where each
          term <c>T</c> has been 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> has been 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>
  </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>