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<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>1996</year><year>2013</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_lint</title>
    <prepared>Robert Virding</prepared>
    <responsible>Bjarne Dacker</responsible>
    <docno>1</docno>
    <approved>Bjarne D&auml;cker</approved>
    <checked></checked>
    <date>97-01-27</date>
    <rev>B</rev>
    <file>erl_lint.sgml</file>
  </header>
  <module>erl_lint</module>
  <modulesummary>The Erlang Code Linter</modulesummary>
  <description>
    <p>This module is used to check Erlang code for illegal syntax and
      other bugs. It also warns against coding practices which are
      not recommended. </p>
    <p>The errors detected include:</p>
    <list type="bulleted">
      <item>redefined and undefined functions</item>
      <item>unbound and unsafe variables</item>
      <item>illegal record usage.</item>
    </list>
    <p>Warnings include:</p>
    <list type="bulleted">
      <item>unused functions and imports</item>
      <item>unused variables</item>
      <item>variables imported into matches</item>
      <item>variables exported from
      <c>if</c>/<c>case</c>/<c>receive</c></item>
      <item>variables shadowed in lambdas and list
       comprehensions.</item>
    </list>
    <p>Some of the warnings are optional, and can be turned on by
      giving the appropriate option, described below.</p>
    <p>The functions in this module are invoked automatically by the
      Erlang compiler and there is no reason to invoke these
      functions separately unless you have written your own Erlang
      compiler.</p>
  </description>
  <datatypes>
    <datatype>
      <name name="error_info"/>
    </datatype>
    <datatype>
      <name name="error_description"/>
    </datatype>
  </datatypes>
  <funcs>
    <func>
      <name name="module" arity="1"/>
      <name name="module" arity="2"/>
      <name name="module" arity="3"/>
      <fsummary>Check a module for errors</fsummary>
      <desc>
        <p>This function checks all the forms in a module for errors.
          It returns:
          </p>
        <taglist>
          <tag><c>{ok,<anno>Warnings</anno>}</c></tag>
          <item>
            <p>There were no errors in the module.</p>
          </item>
          <tag><c>{error,<anno>Errors</anno>,<anno>Warnings</anno>}</c></tag>
          <item>
            <p>There were errors in the module.</p>
          </item>
        </taglist>
        <p>Since this module is of interest only to the maintainers of
          the compiler, and to avoid having the same description in
          two places to avoid the usual maintenance nightmare, the
          elements of <c>Options</c> that control the warnings are
          only described in <seealso marker="compiler:compile#erl_lint_options">compile(3)</seealso>.
          </p>
        <p>The <c><anno>AbsForms</anno></c> of a module which comes from a file
          that is read through <c>epp</c>, the Erlang pre-processor,
          can come from many files. This means that any references to
          errors must include the file name (see <seealso marker="epp">epp(3)</seealso>, or parser <seealso marker="erl_parse">erl_parse(3)</seealso>).
          The warnings and errors returned have the following format:
          </p>
        <code type="none">
    [{<anno>FileName2</anno>,[<anno>ErrorInfo</anno>]}]        </code>
        <p>The errors and warnings are listed in the order in which
          they are encountered in the forms. This means that the
          errors from one file may be split into different entries in
          the list of errors.</p>
      </desc>
    </func>
    <func>
      <name name="is_guard_test" arity="1"/>
      <fsummary>Test for a guard test</fsummary>
      <desc>
        <p>This function tests if <c><anno>Expr</anno></c> is a legal guard test.
          <c><anno>Expr</anno></c> is an Erlang term representing the abstract form
          for the expression. <c>erl_parse:parse_exprs(Tokens)</c> can
          be used to generate a list of <c><anno>Expr</anno></c>.</p>
      </desc>
    </func>
    <func>
      <name name="format_error" arity="1"/>
      <fsummary>Format an error descriptor</fsummary>
      <desc>
        <p>Takes an <c><anno>ErrorDescriptor</anno></c> and returns a string which
          describes the error or warning. This function is usually
          called implicitly when processing an <c>ErrorInfo</c>
          structure (see below).</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 following 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="erl_parse">erl_parse(3)</seealso>,
      <seealso marker="epp">epp(3)</seealso></p>
  </section>
</erlref>

