path: root/lib/compiler/doc/src/compile.xml

<?xml version="1.0" encoding="latin1" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>1996</year><year>2010</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      The contents of this file are subject to the Erlang Public License,
      Version 1.1, (the "License"); you may not use this file except in
      compliance with the License. You should have received a copy of the
      Erlang Public License along with this software. If not, it can be
      retrieved online at http://www.erlang.org/.

      Software distributed under the License is distributed on an "AS IS"
      basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
      the License for the specific language governing rights and limitations
      under the License.

    </legalnotice>

    <title>compile</title>
    <prepared>Robert Virding</prepared>
    <docno></docno>
    <date>1996-11-04</date>
    <rev>A</rev>
    <file>compile.sgml</file>
  </header>
  <module>compile</module>
  <modulesummary>Erlang Compiler</modulesummary>
  <description>
    <p>This module provides an interface to the standard Erlang
      compiler. It can generate either a new file which contains
      the object code, or return a binary which can be loaded directly.
    </p>
  </description>

  <funcs>
    <func>
      <name>file(File)</name>
      <fsummary>Compile a file</fsummary>
      <desc>
        <p>Is the same as
	  <c>file(File, [verbose,report_errors,report_warnings])</c>.
	</p>
      </desc>
    </func>

    <func>
      <name>file(File, Options) -> CompRet</name>
      <fsummary>Compile a file</fsummary>
      <type>
        <v>CompRet = ModRet | BinRet | ErrRet</v>
        <v>ModRet = {ok,ModuleName} | {ok,ModuleName,Warnings}</v>
        <v>BinRet = {ok,ModuleName,Binary} | {ok,ModuleName,Binary,Warnings}</v>
        <v>ErrRet = error | {error,Errors,Warnings}</v>
      </type>
      <desc>
        <p>Compiles the code in the file <c>File</c>, which is an
	  Erlang source code file without the <c>.erl</c> extension.
	  <c>Options</c> determine the behavior of the compiler.</p>

        <p>Returns <c>{ok,ModuleName}</c> if successful, or <c>error</c>
	  if there are errors. An object code file is created if
	  the compilation succeeds with no errors. It is considered
	  to be an error if the module name in the source code is
	  not the same as the basename of the output file.</p>

        <p>Here follows first all elements of <c>Options</c> that in
	  some way control the behavior of the compiler.</p>
        <taglist>
          <tag><c>basic_validation</c></tag>
          <item>
            <p>This option is fast way to test whether a module will
	      compile successfully (mainly useful for code generators
              that want to verify the code they emit). No code will
	      generated. If warnings are enabled, warnings generated by
	      the <c>erl_lint</c> module (such as warnings for unused
	      variables and functions) will be returned too.</p>

            <p>Use the <c>strong_validation</c> option to generate all
	      warnings that the compiler would generate.</p>
          </item>

          <tag><c>strong_validation</c></tag>
          <item>
            <p>Similar to the <c>basic_validation</c> option, no code
	      will be generated, but more compiler passes will be run
	      to ensure also warnings generated by the optimization
	      passes are generated (such as clauses that will not match
	      or expressions that are guaranteed to fail with an
	      exception at run-time).</p>
          </item>

          <tag><c>binary</c></tag>
          <item>
            <p>Causes the compiler to return the object code in a
              binary instead of creating an object file. If successful,
              the compiler returns <c>{ok,ModuleName,Binary}</c>.</p>
          </item>

          <tag><c>bin_opt_info</c></tag>
          <item>
            <p>The compiler will emit informational warnings about binary
	    matching optimizations (both successful and unsuccessful).
	    See the <em>Efficiency Guide</em> for further information.</p>
          </item>

          <tag><c>compressed</c></tag>
          <item>
            <p>The compiler will compress the generated object code,
	    which can be useful for embedded systems.</p>
          </item>

          <tag><c>debug_info</c></tag>
          <item>
            <marker id="debug_info"></marker>
            <p>Include debug information in the form of abstract code
              (see
              <seealso marker="erts:absform">The Abstract Format</seealso>
              in ERTS User's Guide) in the compiled beam module. Tools
	      such as Debugger, Xref and Cover require the debug
              information to be included.</p>

            <p><em>Warning</em>: Source code can be reconstructed from
              the debug information. Use encrypted debug information
              (see below) to prevent this.</p>

            <p>See
              <seealso marker="stdlib:beam_lib#debug_info">beam_lib(3)</seealso>
              for details.</p>
          </item>

          <tag><c>{debug_info_key,KeyString}</c></tag>
          <item></item>
          <tag><c>{debug_info_key,{Mode,KeyString}}</c></tag>
          <item>
            <marker id="debug_info_key"></marker>
            <p>Include debug information, but encrypt it, so that it
              cannot be accessed without supplying the key. (To give
              the <c>debug_info</c> option as well is allowed, but is
              not necessary.) Using this option is a good way to always
              have the debug information available during testing, yet
              protect the source code.</p>
            <p><c>Mode</c> is the type of crypto algorithm to be used
              for encrypting the debug information. The default type --
              and currently the only type -- is <c>des3_cbc</c>.</p>
            <p>See
              <seealso marker="stdlib:beam_lib#debug_info">beam_lib(3)</seealso>
              for details.</p>
          </item>

          <tag><c>encrypt_debug_info</c></tag>
          <item>
            <marker id="encrypt_debug_info"></marker>
            <p>Like the <c>debug_info_key</c> option above, except that
	      the key will be read from an <c>.erlang.crypt</c> file.
	    </p>

	    <p>See
              <seealso marker="stdlib:beam_lib#debug_info">beam_lib(3)</seealso>
              for details.</p>
          </item>

          <tag><c>'P'</c></tag>
          <item>
            <p>Produces a listing of the parsed code after preprocessing
	      and parse transforms, in the file
	      <c><![CDATA[<File>.P]]></c>. No object file is produced.
	    </p>
          </item>

          <tag><c>'E'</c></tag>
          <item>
            <p>Produces a listing of the code after all source code
	      transformations have been performed, in the file
	      <c><![CDATA[<File>.E]]></c>. No object file is produced.
	    </p>
          </item>

          <tag><c>'S'</c></tag>
          <item>
            <p>Produces a listing of the assembler code in the file
              <c><![CDATA[<File>.S]]></c>. No object file is produced.
	    </p>
          </item>

          <tag><c>report_errors/report_warnings</c></tag>
          <item>
            <p>Causes errors/warnings to be printed as they occur.</p>
          </item>

          <tag><c>report</c></tag>
          <item>
            <p>This is a short form for both <c>report_errors</c> and
              <c>report_warnings</c>.</p>
          </item>

          <tag><c>return_errors</c></tag>
          <item>
            <p>If this flag is set, then
	      <c>{error,ErrorList,WarningList}</c> is returned when
	      there are errors.</p>
          </item>

          <tag><c>return_warnings</c></tag>
          <item>
            <p>If this flag is set, then an extra field containing
              <c>WarningList</c> is added to the tuples returned on
              success.</p>
          </item>

          <tag><c>warnings_as_errors</c></tag>
          <item>
            <p>Causes warnings to be treated as errors. This option is supported
            since R13B04.</p>
          </item>

          <tag><c>return</c></tag>
          <item>
            <p>This is a short form for both <c>return_errors</c> and
              <c>return_warnings</c>.</p>
          </item>

	  <tag><c>verbose</c></tag>
          <item>
            <p>Causes more verbose information from the compiler
              describing what it is doing.</p>
          </item>

	  <tag><c>{outdir,Dir}</c></tag>
          <item>
            <p>Sets a new directory for the object code. The current
              directory is used for output, except when a directory
              has been specified with this option.</p>
          </item>

	  <tag><c>export_all</c></tag>
          <item>
            <p>Causes all functions in the module to be exported.</p>
          </item>

	  <tag><c>{i,Dir}</c></tag>
          <item>
            <p>Add <c>Dir</c> to the list of directories to be searched
              when including a file. When encountering an
	      <c>-include</c> or <c>-include_dir</c> directive,
	      the compiler searches for header files in the following
	      directories:</p>
            <list type="ordered">
              <item>
                <p><c>"."</c>, the current working directory of
		  the file server;</p>
              </item>
              <item>
                <p>the base name of the compiled file;</p>
              </item>
              <item>
                <p>the directories specified using the <c>i</c> option.
                  The directory specified last is searched first.</p>
              </item>
            </list>
          </item>

          <tag><c>{d,Macro}</c></tag>
          <item></item>
          <tag><c>{d,Macro,Value}</c></tag>
          <item>
            <p>Defines a macro <c>Macro</c> to have the value
	      <c>Value</c>. The default is <c>true</c>).</p>
          </item>

	  <tag><c>{parse_transform,Module}</c></tag>
          <item>
            <p>Causes the parse transformation function
              <c>Module:parse_transform/2</c> to be applied to the
              parsed code before the code is checked for errors.</p>
          </item>

	  <tag><c>asm</c></tag>
          <item>
            <p>The input file is expected to be assembler code (default
	      file suffix ".S"). Note that the format of assembler files
              is not documented, and may change between releases - this
              option is primarily for internal debugging use.</p>
          </item>

          <tag><c>no_strict_record_tests</c></tag>
          <item>
            <p>This option is not recommended.</p>

	    <p>By default, the generated code for
	      the <c>Record#record_tag.field</c> operation verifies that
	      the tuple <c>Record</c> is of the correct size for
	      the record and that the first element is the tag
	      <c>record_tag</c>. Use this option to omit
	      the verification code.</p>
          </item>

          <tag><c>no_error_module_mismatch</c></tag>
          <item>
            <p>Normally the compiler verifies that the module name
	    given in the source code is the same as the base name
	    of the output file and refuses to generate an output file
	    if there is a mismatch. If you have a good reason (or
	    other reason) for having a module name unrelated to the
	    name of the output file, this option disables that verification
	    (there will not even be a warning if there is a mismatch).</p>
          </item>

        </taglist>

        <p>If warnings are turned on (the <c>report_warnings</c> option
          described above), the following options control what type of
          warnings that will be generated.
	  <marker id="erl_lint_options"></marker>
          With the exception of <c>{warn_format,Verbosity}</c> all
	  options below have two forms; one <c>warn_xxx</c> form to
	  turn on the warning and one <c>nowarn_xxx</c> form to turn off
	  the warning. In the description that follows, the form that
	  is used to change the default value is listed.</p>

        <taglist>
          <tag><c>{warn_format, Verbosity}</c></tag>
          <item>
            <p>Causes warnings to be emitted for malformed format
              strings as arguments to <c>io:format</c> and similar
              functions. <c>Verbosity</c> selects the amount of
              warnings: 0 = no warnings; 1 = warnings for invalid
              format strings and incorrect number of arguments; 2 =
              warnings also when the validity could not be checked
              (for example, when the format string argument is a
              variable). The default verbosity is 1. Verbosity 0 can
              also be selected by the option <c>nowarn_format</c>.</p>
          </item>

          <tag><c>nowarn_bif_clash</c></tag>
          <item>
            <p>By default, there will be a compilation error if a
              module contains an exported function with the same name
              as an auto-imported BIF (such as <c>size/1</c>) AND
              there is a call to it without a qualifying module name.
              The reason is that the BIF will be called, not
	      the function in the same module. The recommended way to
	      eliminate that warning is to use a call with a module
	      name - either <c>erlang</c> to call the BIF or
	      <c>?MODULE</c> to call the function in the same module.
              The warning can also be turned off using this option,
	      but that is not recommended.</p>

	    <p><em>The use of this option is strongly discouraged,
	    as code that uses it will probably break in a future
	    major release (R14 or R15).</em></p>
          </item>

          <tag><c>{nowarn_bif_clash, FAs}</c></tag>
          <item>
            <p>Turns off warnings as <c>nowarn_bif_clash</c> but only
	      for the mentioned local functions. <c>FAs</c> is a tuple
	      <c>{Name,Arity}</c> or a list of such tuples.</p>
	      <p><em>The use of this option is strongly discouraged,
	      as code that uses it will probably break in a future
	      major release (R14 or R15).</em></p>
          </item>

	  <tag><c>warn_export_all</c></tag>
          <item>
            <p>Causes a warning to be emitted if the <c>export_all</c>
	      option has also been given.</p>
          </item>

	  <tag><c>warn_export_vars</c></tag>
          <item>
            <p>Causes warnings to be emitted for all implicitly
              exported variables referred to after the primitives
              where they were first defined. No warnings for exported
              variables unless they are referred to in some pattern,
              which is the default, can be selected by the option
              <c>nowarn_export_vars</c>.</p>
          </item>

	  <tag><c>warn_shadow_vars</c></tag>
          <item>
            <p>Causes warnings to be emitted for "fresh" variables
              in functional objects or list comprehensions with the same
	      name as some already defined variable. The default is to
	      warn for such variables. No warnings for shadowed
	      variables can be selected by the option 
              <c>nowarn_shadow_vars</c>.</p>
          </item>

	  <tag><c>nowarn_unused_function</c></tag>
          <item>
            <p>Turns off warnings for unused local functions.
              By default (<c>warn_unused_function</c>), warnings are
	      emitted for all local functions that are not called
	      directly or indirectly by an exported function.
              The compiler does not include unused local functions in
	      the generated beam file, but the warning is still useful
	      to keep the source code cleaner.</p>
          </item>

	  <tag><c>{nowarn_unused_function, FAs}</c></tag>
          <item>
            <p>Turns off warnings for unused local functions as
              <c>nowarn_unused_function</c> but only for the mentioned
              local functions. <c>FAs</c> is a tuple <c>{Name,Arity}</c>
              or a list of such tuples.</p>
          </item>

	  <tag><c>nowarn_deprecated_function</c></tag>
          <item>
            <p>Turns off warnings for calls to deprecated functions. By
	      default (<c>warn_deprecated_function</c>), warnings are
	      emitted for every call to a function known by the compiler
	      to be deprecated. Note that the compiler does not know
	      about the <c>-deprecated()</c> attribute but uses an
	      assembled list of deprecated functions in Erlang/OTP. To
	      do a more general check the <c>Xref</c> tool can be used.
	      See also
	      <seealso marker="tools:xref#deprecated_function">xref(3)</seealso>
              and the function
	      <seealso marker="tools:xref#m/1">xref:m/1</seealso> also
              accessible through
	      the <seealso marker="stdlib:c#xm/1">c:xm/1</seealso>
	      function.</p>
          </item>

	  <tag><c>{nowarn_deprecated_function, MFAs}</c></tag>
          <item>
            <p>Turns off warnings for calls to deprecated functions as
	      <c>nowarn_deprecated_function</c> but only for
	      the mentioned functions. <c>MFAs</c> is a tuple
              <c>{Module,Name,Arity}</c> or a list of such tuples.</p>
          </item>

	  <tag><c>warn_obsolete_guard</c></tag>
          <item>
            <p>Causes warnings to be emitted for calls to old type
	      testing BIFs such as <c>pid/1</c> and <c>list/1</c>. See
	      the
	      <seealso marker="doc/reference_manual:expressions#guards">Erlang Reference Manual</seealso>
	      for a complete list of type testing BIFs and their old
	      equivalents. No warnings for calls to old type testing
	      BIFs, which is the default, can be selected by the option
              <c>nowarn_obsolete_guard</c>.</p>
          </item>

	  <tag><c>warn_unused_import</c></tag>
          <item>
            <p>Causes warnings to be emitted for unused imported
              functions. No warnings for unused imported functions,
	      which is the default, can be selected by the option
              <c>nowarn_unused_import</c>. </p>
          </item>

          <tag><c>nowarn_unused_vars</c></tag>
          <item>
            <p>By default, warnings are emitted for variables which
              are not used, with the exception of variables beginning
              with an underscore ("Prolog style warnings").
              Use this option to turn off this kind of warnings.</p>
          </item>

	  <tag><c>nowarn_unused_record</c></tag>
          <item>
            <p>Turns off warnings for unused record types. By
              default (<c>warn_unused_records</c>), warnings are
              emitted for unused locally defined record types.</p>
          </item>
        </taglist>

	<p>Another class of warnings is generated by the compiler
	  during optimization and code generation. They warn about
	  patterns that will never match (such as <c>a=b</c>), guards
	  that will always evaluate to false, and expressions that will
	  always fail (such as <c>atom+42</c>).</p>

        <p>Note that the compiler does not warn for expressions that it
          does not attempt to optimize. For instance, the compiler tries
          to evaluate <c>1/0</c>, notices that it will cause an
	  exception and emits a warning. On the other hand,
	  the compiler is silent about the similar expression
	  <c>X/0</c>; because of the variable in it, the compiler does
	  not even try to evaluate and therefore it emits no warnings.
	</p>

	<p>Currently, those warnings cannot be disabled (except by
	  disabling all warnings).</p>

	<warning>
          <p>Obviously, the absence of warnings does not mean that
	    there are no remaining errors in the code.</p>
        </warning>

	<p>Note that all the options except the include path
	  (<c>{i,Dir}</c>) can also be given in the file with a
	  <c>-compile([Option,...])</c>. attribute.
	  The <c>-compile()</c> attribute is allowed after function
	  definitions.</p>

	<p>Note also that the <c>{nowarn_unused_function, FAs}</c>,
          <c>{nowarn_bif_clash, FAs}</c>, and 
          <c>{nowarn_deprecated_function, MFAs}</c> options are only
          recognized when given in files. They are not affected by
	  the <c>warn_unused_function</c>, <c>warn_bif_clash</c>, or 
          <c>warn_deprecated_function</c> options.</p>

        <p>For debugging of the compiler, or for pure curiosity,
          the intermediate code generated by each compiler pass can be
	  inspected.
          A complete list of the options to produce list files can be
	  printed by typing <c>compile:options()</c> at the Erlang
	  shell prompt.
          The options will be printed in order that the passes are
	  executed. If more than one listing option is used, the one
	  representing the earliest pass takes effect.</p>

        <p><em>Unrecognized options are ignored.</em></p>

        <p>Both <c>WarningList</c> and <c>ErrorList</c> have
	  the following format:</p>
        <code>
[{FileName,[ErrorInfo]}].
        </code>

	<p><c>ErrorInfo</c> is described below. The file name has been
	  included here as the compiler uses the Erlang pre-processor
	  <c>epp</c>, which allows the code to be included in other
	  files. For this reason, it is important to know to
	  <em>which</em> file an error or warning line number refers.
	</p>
      </desc>
    </func>

    <func>
      <name>forms(Forms)</name>
      <fsummary>Compile a list of forms</fsummary>
      <desc>
        <p>Is the same as
	  <c>forms(File, [verbose,report_errors,report_warnings])</c>.
	</p>
      </desc>
    </func>

    <func>
      <name>forms(Forms, Options) -> CompRet</name>
      <fsummary>Compile a list of forms</fsummary>
      <type>
        <v>Forms = [Form]</v>
        <v>CompRet = BinRet | ErrRet</v>
        <v>BinRet = {ok,ModuleName,BinaryOrCode} | {ok,ModuleName,BinaryOrCode,Warnings}</v>
        <v>BinaryOrCode = binary() | term()</v>
        <v>ErrRet = error | {error,Errors,Warnings}</v>
      </type>
      <desc>
        <p>Analogous to <c>file/1</c>, but takes a list of forms (in
	  the Erlang abstract format representation) as first argument.
          The option <c>binary</c> is implicit; i.e., no object code
	  file is produced. Options that would ordinarily produce a
	  listing file, such as 'E', will instead cause the internal
	  format for that compiler pass (an Erlang term; usually not a
	  binary) to be returned instead of a binary.</p>
      </desc>
    </func>

    <func>
      <name>format_error(ErrorDescriptor) -> chars()</name>
      <fsummary>Format an error descriptor</fsummary>
      <type>
        <v>ErrorDescriptor = errordesc()</v>
      </type>
      <desc>
        <p>Uses an <c>ErrorDescriptor</c> and returns a deep list of
	  characters 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>output_generated(Options) -> true | false</name>
      <fsummary>Determine whether the compile will generate an output file</fsummary>
      <type>
        <v>Options = [term()]</v>
      </type>
      <desc>
        <p>Determines whether the compiler would generate a <c>beam</c>
	file with the given options. <c>true</c> means that a <c>beam</c>
	file would be generated; <c>false</c> means that the compiler
	would generate some listing file, return a binary, or merely
	check the syntax of the source code.</p>
      </desc>
    </func>

    <func>
      <name>noenv_file(File, Options) -> CompRet</name>
      <fsummary>Compile a file (ignoring ERL_COMPILER_OPTIONS)</fsummary>
      <desc>
      <p>Works exactly like <seealso marker="#file/2">file/2</seealso>,
	 except that the environment variable <c>ERL_COMPILER_OPTIONS</c>
	 is not consulted.</p>
      </desc>
    </func>

    <func>
      <name>noenv_forms(Forms, Options) -> CompRet</name>
      <fsummary>Compile a list of forms (ignoring ERL_COMPILER_OPTIONS)</fsummary>
      <desc>
        <p>Works exactly like <seealso marker="#forms/2">forms/2</seealso>,
	 except that the environment variable <c>ERL_COMPILER_OPTIONS</c>
	 is not consulted.</p>
      </desc>
    </func>

    <func>
      <name>noenv_output_generated(Options) -> true | false</name>
      <fsummary>Determine whether the compile will generate an output file (ignoring ERL_COMPILER_OPTIONS)</fsummary>
      <type>
        <v>Options = [term()]</v>
      </type>
      <desc>
        <p>Works exactly like
	<seealso marker="#output_generated/1">output_generated/1</seealso>,
	except that the environment variable <c>ERL_COMPILER_OPTIONS</c>
	is not consulted.</p>
      </desc>
    </func>

  </funcs>

  <section>
    <title>Default compiler options</title>
    <p>The (host operating system) environment variable
      <c>ERL_COMPILER_OPTIONS</c> can be used to give default compiler
      options. Its value must be a valid Erlang term. If the value is a
      list, it will be used as is. If it is not a list, it will be put
      into a list.</p>

      <p>The list will be appended to any options given to
      <seealso marker="#file/2">file/2</seealso>,
      <seealso marker="#forms/2">forms/2</seealso>, and
      <seealso marker="#output_generated/1">output_generated/2</seealso>.
      Use the alternative functions
      <seealso marker="#noenv_file/2">noenv_file/2</seealso>,
      <seealso marker="#noenv_forms/2">noenv_forms/2</seealso>, or
      <seealso marker="#noenv_output_generated/1">noenv_output_generated/2</seealso>
      if you don't want the environment variable to be consulted
      (for instance, if you are calling the compiler recursively from
      inside a parse transform).</p>
  </section>

  <section>
    <title>Inlining</title>
    <p>The compiler can do function inlining within an Erlang
      module. Inlining means that a call to a function is replaced with
      the function body with the arguments replaced with the actual
      values. The semantics are preserved, except if exceptions are
      generated in the inlined code. Exceptions will be reported as
      occurring in the function the body was inlined into. Also,
      <c>function_clause</c> exceptions will be converted to similar
      <c>case_clause</c> exceptions.</p>

    <p>When a function is inlined, the original function will be
      kept if it is exported (either by an explicit export or if the
      <c>export_all</c> option was given) or if not all calls to the
      function were inlined.</p>
    
    <p>Inlining does not necessarily improve running time.
      For instance, inlining may increase Beam stack usage which will
      probably be detrimental to performance for recursive functions.
    </p>

    <p>Inlining is never default; it must be explicitly enabled with a
      compiler option or a <c>-compile()</c> attribute in the source
      module.</p>

    <p>To enable inlining, either use the <c>inline</c> option to
    let the compiler decide which functions to inline or
    <c>{inline,[{Name,Arity},...]}</c> to have the compiler inline
    all calls to the given functions. If the option is given inside
    a <c>compile</c> directive in an Erlang module, <c>{Name,Arity}</c>
    may be written as <c>Name/Arity</c>.</p>

    <p>Example of explicit inlining:</p>

    <pre>
-compile({inline,[pi/0]}).

pi() -> 3.1416.
    </pre>

    <p>Example of implicit inlining:</p>
    <pre>
-compile(inline).
    </pre>

    <p>The <c>{inline_size,Size}</c> option controls how large functions
      that are allowed to be inlined. Default is <c>24</c>, which will
      keep the size of the inlined code roughly the same as
      the un-inlined version (only relatively small functions will be
      inlined).</p>

    <p>Example:</p>
    <pre>
%% Aggressive inlining - will increase code size.
-compile(inline).
-compile({inline_size,100}).
    </pre>
  </section>

  <section>
    <title>Parse Transformations</title>

    <p>Parse transformations are used when a programmer wants to use
      Erlang syntax but with different semantics. The original Erlang
      code is then transformed into other Erlang code.</p>
  </section>

  <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>
{ErrorLine, Module, ErrorDescriptor}
    </code>

    <p>A string describing the error is obtained with the following
      call:</p>
    <code>
Module:format_error(ErrorDescriptor)
    </code>
  </section>

  <section>
    <title>See Also</title>
    <p>
      <seealso marker="stdlib:epp">epp(3)</seealso>,
      <seealso marker="stdlib:erl_id_trans">erl_id_trans(3)</seealso>,
      <seealso marker="stdlib:erl_lint">erl_lint(3)</seealso>,
      <seealso marker="stdlib:beam_lib">beam_lib(3)</seealso>
    </p>
  </section>
</erlref>