Erlang Compiler
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.
Functions
Return compiler options given via the environment variable
ERL_COMPILER_OPTIONS
. If the value is a list, it is
returned as is. If it is not a list, it is put into a list.
Is the same as
file(File, [verbose,report_errors,report_warnings])
.
CompRet = ModRet | BinRet | ErrRet
ModRet = {ok,ModuleName} | {ok,ModuleName,Warnings}
BinRet = {ok,ModuleName,Binary} | {ok,ModuleName,Binary,Warnings}
ErrRet = error | {error,Errors,Warnings}
Compiles the code in the file File
, which is an
Erlang source code file without the .erl
extension.
Options
determine the behavior of the compiler.
Returns {ok,ModuleName}
if successful, or error
if there are errors. An object code file is created if
the compilation succeeds without 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.
Available options:
basic_validation
This option is a fast way to test whether a module will
compile successfully. This is useful for code generators
that want to verify the code that they emit. No code is
generated. If warnings are enabled, warnings generated by
the erl_lint
module (such as warnings for unused
variables and functions) are also returned.
Use option strong_validation
to generate all
warnings that the compiler would generate.
strong_validation
Similar to option basic_validation
. No code
is generated, but more compiler passes are run
to ensure that 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 runtime).
binary
The compiler returns the object code in a
binary instead of creating an object file. If successful,
the compiler returns {ok,ModuleName,Binary}
.
bin_opt_info
The compiler will emit informational warnings about binary matching optimizations (both successful and unsuccessful). For more information, see the section about bin_opt_info in the Efficiency Guide.
{compile_info, [{atom(), term()}]}
Allows compilers built on top of compile
to attach
extra compilation metadata to the compile_info
chunk
in the generated beam file.
It is advised for compilers to remove all non-deterministic
information if the deterministic
option is supported and
it was supplied by the user.
compressed
The compiler will compress the generated object code, which can be useful for embedded systems.
debug_info
Includes debug information in the form of
Erlang Abstract Format in the debug_info
chunk of the compiled beam module. Tools such as Debugger,
Xref, and Cover require the debug information to be included.
Warning: Source code can be reconstructed from
the debug information. Use encrypted debug information
(encrypt_debug_info
) to prevent this.
For details, see beam_lib(3).
{debug_info, {Backend, Data}}
Includes custom debug information in the form of a
Backend
module with custom Data
in the compiled beam module.
The given module must implement a debug_info/4
function
and is responsible for generating different code representations,
as described in the debug_info
under
beam_lib(3).
Warning: Source code can be reconstructed from
the debug information. Use encrypted debug information
(encrypt_debug_info
) to prevent this.
{debug_info_key,KeyString}
{debug_info_key,{Mode,KeyString}}
Includes debug information, but encrypts it so that it
cannot be accessed without supplying the key. (To give
option debug_info
as well is allowed, but
not necessary.) Using this option is a good way to always
have the debug information available during testing, yet
protecting the source code.
Mode
is the type of crypto algorithm to be used
for encrypting the debug information. The default
(and currently the only) type is des3_cbc
.
For details, see beam_lib(3).
encrypt_debug_info
Similar to the debug_info_key
option, but
the key is read from an .erlang.crypt
file.
For details, see beam_lib(3).
deterministic
Omit the options
and source
tuples in
the list returned by Module:module_info(compile)
, and
reduce the paths in stack traces to the module name alone.
This option will make it easier to achieve reproducible builds.
makedep
Produces a Makefile rule to track headers dependencies. No object file is produced.
By default, this rule is written to
<File>.Pbeam
. However, if option
binary
is set, nothing is written and the rule is
returned in Binary
.
For example, if you have the following module:
-module(module).
-include_lib("eunit/include/eunit.hrl").
-include("header.hrl").
The Makefile rule generated by this option looks as follows:
module.beam: module.erl \
/usr/local/lib/erlang/lib/eunit/include/eunit.hrl \
header.hrl
makedep_side_effect
The dependecies are created as a side effect to the
normal compilation process. This means that the object
file will also be produced. This option override the
makedep
option.
{makedep_output, Output}
Writes generated rules to Output
instead of the
default <File>.Pbeam
. Output
can be a filename or an io_device()
. To write to
stdout, use standard_io
. However, if binary
is set, nothing is written to Output
and the
result is returned to the caller with
{ok, ModuleName, Binary}
.
{makedep_target, Target}
Changes the name of the rule emitted to Target
.
makedep_quote_target
Characters in Target
special to make(1) are quoted.
makedep_add_missing
Considers missing headers as generated files and adds them to the dependencies.
makedep_phony
Adds a phony target for each dependency.
'P'
Produces a listing of the parsed code, after preprocessing
and parse transforms, in the file
<File>.P
. No object file is produced.
'E'
Produces a listing of the code, after all source code
transformations have been performed, in the file
<File>.E
. No object file is produced.
'S'
Produces a listing of the assembler code in the file
<File>.S
. No object file is produced.
report_errors/report_warnings
Causes errors/warnings to be printed as they occur.
report
A short form for both report_errors
and
report_warnings
.
return_errors
If this flag is set,
{error,ErrorList,WarningList}
is returned when
there are errors.
return_warnings
If this flag is set, an extra field, containing
WarningList
, is added to the tuples returned on
success.
warnings_as_errors
Causes warnings to be treated as errors. This option is supported since R13B04.
return
A short form for both return_errors
and
return_warnings
.
verbose
Causes more verbose information from the compiler, describing what it is doing.
{source,FileName}
Overrides the source file name as presented in
module_info(compile)
and stack traces.
{outdir,Dir}
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.
export_all
Causes all functions in the module to be exported.
{i,Dir}
Adds Dir
to the list of directories to be searched
when including a file. When encountering an
-include
or -include_lib
directive,
the compiler searches for header files in the following
directories:
-
"."
, the current working directory of the file server -
The base name of the compiled file
-
The directories specified using option
i
; the directory specified last is searched first
{d,Macro}
{d,Macro,Value}
Defines a macro Macro
to have the value
Value
. Macro
is of type atom, and Value
can be any term.
The default Value
is true
.
{parse_transform,Module}
Causes the parse transformation function
Module:parse_transform/2
to be applied to the
parsed code before the code is checked for errors.
from_asm
The input file is expected to be assembler code (default file suffix ".S"). Notice that the format of assembler files is not documented, and can change between releases.
from_core
The input file is expected to be core code (default file suffix ".core"). Notice that the format of core files is not documented, and can change between releases.
no_spawn_compiler_process
By default, all code is compiled in a separate process which is terminated at the end of compilation. However, some tools, like Dialyzer or compilers for other BEAM languages, may already manage their own worker processes and spawning an extra process may slow the compilation down. In such scenarios, you can pass this option to stop the compiler from spawning an additional process.
no_strict_record_tests
This option is not recommended.
By default, the generated code for
operation Record#record_tag.field
verifies that
the tuple Record
has the correct size for
the record, and that the first element is the tag
record_tag
. Use this option to omit
the verification code.
no_error_module_mismatch
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).
{no_auto_import,[{F,A}, ...]}
Makes the function F/A
no longer being
auto-imported from the erlang
module, which resolves
BIF name clashes. This option must be used to resolve name
clashes with BIFs auto-imported before R14A, if it is needed to
call the local function with the same name as an
auto-imported BIF without module prefix.
Note!
As from R14A and forward, the compiler resolves calls
without module prefix to local or imported functions before
trying with auto-imported BIFs. If the BIF is to be
called, use the erlang
module prefix in the call, not
{no_auto_import,[{F,A}, ...]}
.
If this option is written in the source code, as a
-compile
directive, the syntax F/A
can be used instead
of {F,A}
, for example:
-compile({no_auto_import,[error/1]}).
no_auto_import
Do not auto-import any functions from erlang
module.
no_line_info
Omits line number information to produce a slightly smaller output file.
{extra_chunks, [{binary(), binary()}]}
Pass extra chunks to be stored in the .beam
file.
The extra chunks must be a list of tuples with a four byte
binary as chunk name followed by a binary with the chunk contents.
See beam_lib for
more information.
If warnings are turned on (option report_warnings
described earlier), the following options control what type of
warnings that are generated.
Except from {warn_format,Verbosity}
, the following options
have two forms:
- A
warn_xxx
form, to turn on the warning. - A
nowarn_xxx
form, to turn off the warning.
In the descriptions that follow, the form that is used to change the default value are listed.
{warn_format, Verbosity}
Causes warnings to be emitted for malformed format
strings as arguments to io:format
and similar
functions.
Verbosity
selects the number of warnings:
0
= No warnings1
= Warnings for invalid format strings and incorrect number of arguments2
= Warnings also when the validity cannot be checked, for example, when the format string argument is a variable.
The default verbosity is 1
. Verbosity 0
can
also be selected by option nowarn_format
.
nowarn_bif_clash
This option is removed, it generates a fatal error if used.
Warning!
As from 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 nowarn_bif_clash
would
make a module calling functions clashing with auto-imported BIFs
compile with both the old and new compilers, but with
completely different semantics. This is why the option is removed.
The use of this option has always been discouraged. As from R14A, it is an error to use it.
To resolve BIF clashes, use explicit module names or the
{no_auto_import,[F/A]}
compiler directive.
{nowarn_bif_clash, FAs}
This option is removed, it generates a fatal error if used.
Warning!
The use of this option has always been discouraged. As from R14A, it is an error to use it.
To resolve BIF clashes, use explicit module names or the
{no_auto_import,[F/A]}
compiler directive.
nowarn_export_all
Turns off warnings for uses of the export_all
option. Default is to emit a warning if option
export_all
is also given.
warn_export_vars
Emits warnings for all implicitly exported variables referred to after the primitives where they were first defined. By default, the compiler only emits warnings for exported variables referred to in a pattern.
nowarn_shadow_vars
Turns off warnings for "fresh" variables in functional objects or list comprehensions with the same name as some already defined variable. Default is to emit warnings for such variables.
nowarn_unused_function
Turns off warnings for unused local functions. Default is to emit warnings 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.
{nowarn_unused_function, FAs}
Turns off warnings for unused local functions like
nowarn_unused_function
does, but only for the mentioned
local functions. FAs
is a tuple {Name,Arity}
or a list of such tuples.
nowarn_deprecated_function
Turns off warnings for calls to deprecated functions. Default
is to emit warnings for every call to a function known by the
compiler to be deprecated. Notice that the compiler does not know
about attribute -deprecated()
, but uses an
assembled list of deprecated functions in Erlang/OTP. To
do a more general check, the Xref tool can be used.
See also
xref(3)
and the function
xref:m/1, also
accessible through the function
c:xm/1.
{nowarn_deprecated_function, MFAs}
Turns off warnings for calls to deprecated functions like
nowarn_deprecated_function
does, but only for
the mentioned functions. MFAs
is a tuple
{Module,Name,Arity}
or a list of such tuples.
nowarn_deprecated_type
Turns off warnings for use of deprecated types. Default is to emit warnings for every use of a type known by the compiler to be deprecated.
nowarn_removed
Turns off warnings for calls to functions that have been removed. Default is to emit warnings for every call to a function known by the compiler to have been recently removed from Erlang/OTP.
{nowarn_removed, ModulesOrMFAs}
Turns off warnings for calls to modules or functions that have been removed. Default is to emit warnings for every call to a function known by the compiler to have been recently removed from Erlang/OTP.
nowarn_obsolete_guard
Turns off warnings for calls to old type testing BIFs,
such as pid/1
and list/1
. See the
Erlang Reference Manual
for a complete list of type testing BIFs and their old
equivalents. Default is to emit warnings for calls to
old type testing BIFs.
warn_unused_import
Emits warnings for unused imported functions. Default is to emit no warnings for unused imported functions.
nowarn_unused_vars
By default, warnings are emitted for unused variables, except for variables beginning with an underscore ("Prolog style warnings"). Use this option to turn off this kind of warnings.
nowarn_unused_record
Turns off warnings for unused record types. Default is to emit warnings for unused locally defined record types.
Another class of warnings is generated by the compiler
during optimization and code generation. They warn about
patterns that will never match (such as a=b
), guards
that always evaluate to false, and expressions that
always fail (such as atom+42
).
Those warnings cannot be disabled (except by disabling all warnings).
Note!
The compiler does not warn for expressions that it
does not attempt to optimize. For example, the compiler tries
to evaluate 1/0
, detects that it will cause an
exception, and emits a warning. However,
the compiler is silent about the similar expression,
X/0
, because of the variable in it. Thus, the compiler does
not even try to evaluate and therefore it emits no warnings.
Warning!
The absence of warnings does not mean that there are no remaining errors in the code.
Note!
All options, except the include path
({i,Dir}
), can also be given in the file with attribute
-compile([Option,...])
.
Attribute -compile()
is allowed after the function
definitions.
Note!
Before OTP 22, the option {nowarn_deprecated_function,
MFAs}
was only recognized when given in the file with
attribute -compile()
. (The option
{nowarn_unused_function,FAs}
was incorrectly documented
to only work in a file, but it also worked when given in the
option list.) Starting from OTP 22, all options that can be
given in the file can also be given in the option list.
For debugging of the compiler, or for pure curiosity,
the intermediate code generated by each compiler pass can be
inspected.
To print a complete list of the options to produce list files,
type compile:options()
at the Erlang shell prompt.
The options are printed in the order that the passes are
executed. If more than one listing option is used, the one
representing the earliest pass takes effect.
Unrecognized options are ignored.
Both WarningList
and ErrorList
have
the following format:
[{FileName,[ErrorInfo]}].
ErrorInfo
is described later in this section.
The filename is included here, as the compiler uses the
Erlang pre-processor epp
, which allows the code to be
included in other files. It is therefore important to know to
which file the line number of an error or a warning refers.
Is the same as
forms(Forms, [verbose,report_errors,report_warnings])
.
Forms = [Form]
CompRet = BinRet | ErrRet
BinRet = {ok,ModuleName,BinaryOrCode} | {ok,ModuleName,BinaryOrCode,Warnings}
BinaryOrCode = binary() | term()
ErrRet = error | {error,Errors,Warnings}
Analogous to file/1
, but takes a list of forms (in
the Erlang abstract format representation) as first argument.
Option binary
is implicit, that is, no object code
file is produced. For options that normally produce a listing
file, such as 'E', the internal format for that compiler pass
(an Erlang term, usually not a binary) is returned instead of
a binary.
ErrorDescriptor = errordesc()
Uses an ErrorDescriptor
and returns a deep list of
characters that describes the error. This function is
usually called implicitly when an ErrorInfo
structure
(described in section
Error Information) is processed.
Options = [term()]
Determines whether the compiler generates a beam
file with the given options. true
means that a beam
file is generated. false
means that the compiler
generates some listing file, returns a binary, or merely
checks the syntax of the source code.
Works like file/2,
except that the environment variable ERL_COMPILER_OPTIONS
is not consulted.
Works like forms/2,
except that the environment variable ERL_COMPILER_OPTIONS
is not consulted.
Options = [term()]
Works like
output_generated/1,
except that the environment variable ERL_COMPILER_OPTIONS
is not consulted.
Default Compiler Options
The (host operating system) environment variable
ERL_COMPILER_OPTIONS
can be used to give default compiler
options. Its value must be a valid Erlang term. If the value is a
list, it is used as is. If it is not a list, it is put
into a list.
The list is appended to any options given to file/2, forms/2, and output_generated/2. Use the alternative functions noenv_file/2, noenv_forms/2, or noenv_output_generated/2 if you do not want the environment variable to be consulted, for example, if you are calling the compiler recursively from inside a parse transform.
The list can be retrieved with env_compiler_options/0.
Inlining
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 are reported as
occurring in the function the body was inlined into. Also,
function_clause
exceptions are converted to similar
case_clause
exceptions.
When a function is inlined, the original function is
kept if it is exported (either by an explicit export or if the
option export_all
was given) or if not all calls to the
function are inlined.
Inlining does not necessarily improve running time. For example, inlining can increase Beam stack use, which probably is detrimental to performance for recursive functions.
Inlining is never default. It must be explicitly enabled with a
compiler option or a -compile()
attribute in the source
module.
To enable inlining, either use the option inline
to
let the compiler decide which functions to inline, or
{inline,[{Name,Arity},...]}
to have the compiler inline
all calls to the given functions. If the option is given inside
a compile
directive in an Erlang module, {Name,Arity}
can be written as Name/Arity
.
Example of explicit inlining:
-compile({inline,[pi/0]}). pi() -> 3.1416.
Example of implicit inlining:
-compile(inline).
The option {inline_size,Size}
controls how large functions
that are allowed to be inlined. Default is 24
, which
keeps the size of the inlined code roughly the same as
the un-inlined version (only relatively small functions are
inlined).
Example:
%% Aggressive inlining - will increase code size. -compile(inline). -compile({inline_size,100}).
Inlining of List Functions
The compiler can also inline various list manipulation functions
from the module list
in STDLIB.
This feature must be explicitly enabled with a compiler option or a
-compile()
attribute in the source module.
To enable inlining of list functions, use option inline_list_funcs
.
The following functions are inlined:
Parse Transformations
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.
Error Information
The ErrorInfo
mentioned earlier is the standard
ErrorInfo
structure, which is returned from all I/O modules.
It has the following format:
{ErrorLine, Module, ErrorDescriptor}
ErrorLine
is the atom none
if the error does
not correspond to a specific line, for example, if the source file does
not exist.
A string describing the error is obtained with the following call:
Module:format_error(ErrorDescriptor)