<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">
<erlref>
<header>
<copyright>
<year>1996</year><year>2013</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><marker id="type-option"/>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>makedep</c></tag>
<item>
<p>Produce a Makefile rule to track headers dependencies.
No object file is produced.
</p>
<p>By default, this rule is written to
<c><![CDATA[<File>.Pbeam]]></c>. However, if the option
<c>binary</c> is set, nothing is written and the rule is
returned in <c>Binary</c>.
</p>
<p>For instance, if one has the following module:
</p>
<code>
-module(module).
-include_lib("eunit/include/eunit.hrl").
-include("header.hrl").
</code>
<p>Here is the Makefile rule generated by this option:
</p>
<code>
module.beam: module.erl \
/usr/local/lib/erlang/lib/eunit/include/eunit.hrl \
header.hrl
</code>
</item>
<tag><c>{makedep_output, Output}</c></tag>
<item>
<p>Write generated rule(s) to <c>Output</c> instead of the
default <c><![CDATA[<File>.Pbeam]]></c>. <c>Output</c>
can be a filename or an <c>io_device()</c>. To write to
stdout, use <c>standard_io</c>. However if <c>binary</c>
is set, nothing is written to <c>Output</c> and the
result is returned to the caller with
<c>{ok, ModuleName, Binary}</c>.
</p>
</item>
<tag><c>{makedep_target, Target}</c></tag>
<item>
<p>Change the name of the rule emitted to <c>Target</c>.
</p>
</item>
<tag><c>makedep_quote_target</c></tag>
<item>
<p>Characters in <c>Target</c> special to make(1) are quoted.
</p>
</item>
<tag><c>makedep_add_missing</c></tag>
<item>
<p>Consider missing headers as generated files and add them to the
dependencies.
</p>
</item>
<tag><c>makedep_phony</c></tag>
<item>
<p>Add a phony target for each dependency.
</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>{source,FileName}</c></tag>
<item>
<p>Sets the value of the source, as returned by
<c>module_info(compile)</c>.</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_lib</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>. <c>Macro</c> is of type atom, and <c>Value</c> can be any term.
The default <c>Value</c> 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>
<tag><c>{no_auto_import,[{F,A}, ...]}</c></tag>
<item>
<p>Makes the function <c>F/A</c> no longer being
auto-imported from the module <c>erlang</c>, which resolves
BIF name clashes. This option has to be used to resolve name
clashes with BIFs auto-imported before R14A, if one wants to
call the local function with the same name as an
auto-imported BIF without module prefix.</p>
<note>
<p>From R14A and forward, the compiler resolves calls
without module prefix to local or imported functions before
trying auto-imported BIFs. If the BIF is to be
called, use the <c>erlang</c> module prefix in the call, not
<c>{ no_auto_import,[{F,A}, ...]}</c></p>
</note>
<p>If this option is written in the source code, as a
<c>-compile</c> directive, the syntax <c>F/A</c> can be used instead
of <c>{F,A}</c>. Example:</p>
<code>-compile({no_auto_import,[error/1]}).</code>
</item>
<tag><c>no_line_info</c></tag>
<item>
<p>Omit line number information in order to produce a slightly
smaller output file.
</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>This option is removed, it will generate a fatal error if used.</p>
<warning>
<p>Beginning with R14A, the compiler no longer calls the
auto-imported BIF if the name clashes with a local or
explicitly imported function and a call without explicit
module name is issued. Instead the local or imported
function is called. Still accepting <c>nowarn_bif_clash</c> would makes a
module calling functions clashing with autoimported BIFs
compile with both the old and new compilers, but with
completely different semantics, why the option was removed.</p>
<p>The use of this option has always been strongly discouraged.
From OTP R14A and forward it's an error to use it.</p>
<p>To resolve BIF clashes, use explicit module names or the
<c>{no_auto_import,[F/A]}</c> compiler directive.</p>
</warning>
</item>
<tag><c>{nowarn_bif_clash, FAs}</c></tag>
<item>
<p>This option is removed, it will generate a fatal error if used.</p>
<warning>
<p>The use of this option has always been strongly discouraged.
From OTP R14A and forward it's an error to use it.</p>
<p>To resolve BIF clashes, use explicit module names or the
<c>{no_auto_import,[F/A]}</c> compiler directive.</p>
</warning>
</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>Inlining of list functions</title>
<p>The compiler can also inline a variety of list manipulation functions
from the stdlib's lists module.</p>
<p>This feature must be explicitly enabled with a compiler option or a
<c>-compile()</c> attribute in the source module.</p>
<p>To enable inlining of list functions, use the <c>inline_list_funcs</c>
option.</p>
<p>The following functions are inlined:</p>
<list type="bulleted">
<item><seealso marker="stdlib:lists#all/2">lists:all/2</seealso></item>
<item><seealso marker="stdlib:lists#any/2">lists:any/2</seealso></item>
<item><seealso marker="stdlib:lists#foreach/2">lists:foreach/2</seealso></item>
<item><seealso marker="stdlib:lists#map/2">lists:map/2</seealso></item>
<item><seealso marker="stdlib:lists#flatmap/2">lists:flatmap/2</seealso></item>
<item><seealso marker="stdlib:lists#filter/2">lists:filter/2</seealso></item>
<item><seealso marker="stdlib:lists#foldl/3">lists:foldl/3</seealso></item>
<item><seealso marker="stdlib:lists#foldr/3">lists:foldr/3</seealso></item>
<item><seealso marker="stdlib:lists#mapfoldl/3">lists:mapfoldl/3</seealso></item>
<item><seealso marker="stdlib:lists#mapfoldr/3">lists:mapfoldr/3</seealso></item>
</list>
</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><c>ErrorLine</c> will be the atom <c>none</c> if the error does
not correspond to a specific line (e.g. if the source file does
not exist).</p>
<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>
