compile(3erl)
NAME
compile - Erlang Compiler
DESCRIPTION
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.
EXPORTS
env_compiler_options()
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.
file(File)
Is the same as file(File,
[verbose,report_errors,report_warnings]).
file(File, Options) -> CompRet
Types:
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.
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 abstract code (see
The Abstract Format in ERTS User's Guide) in 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(3erl).
{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(3erl).
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(3erl).
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_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}:
Sets the value of the source, as returned by
module_info(compile).
{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_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.
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 warnings
* 1 = Warnings for invalid format strings and incorrect
number of arguments
* 2 = 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.
warn_export_all:
Emits 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(3erl) 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.
warn_obsolete_guard:
Emits 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 no 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:
The options {nowarn_unused_function, FAs}, {nowarn_bif_clash,
FAs}, and {nowarn_deprecated_function, MFAs} are only recognized
when given in files. They are not affected by options
warn_unused_function, warn_bif_clash, or
warn_deprecated_function.
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.
forms(Forms)
Is the same as forms(File,
[verbose,report_errors,report_warnings]).
forms(Forms, Options) -> CompRet
Types:
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.
format_error(ErrorDescriptor) -> chars()
Types:
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.
output_generated(Options) -> true | false
Types:
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.
noenv_file(File, Options) -> CompRet
Works like file/2, except that the environment variable
ERL_COMPILER_OPTIONS is not consulted.
noenv_forms(Forms, Options) -> CompRet
Works like forms/2, except that the environment variable
ERL_COMPILER_OPTIONS is not consulted.
noenv_output_generated(Options) -> true | false
Types:
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:
* lists:all/2
* lists:any/2
* lists:foreach/2
* lists:map/2
* lists:flatmap/2
* lists:filter/2
* lists:foldl/3
* lists:foldr/3
* lists:mapfoldl/3
* lists:mapfoldr/3
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)
SEE ALSO
epp(3erl), erl_id_trans(3erl), erl_lint(3erl), beam_lib(3erl)
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