Provided by: erlang-manpages_20.2.2+dfsg-1ubuntu2_all bug


       compile - 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



              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


              Is the same as file(File, [verbose,report_errors,report_warnings]).

       file(File, Options) -> CompRet


                 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:

                  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

                  Use  option  strong_validation to generate all warnings that the compiler would

                  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).

                  The  compiler returns the object code in a binary instead of creating an object
                  file. If successful, the compiler returns {ok,ModuleName,Binary}.

                  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.

                  The compiler will compress the generated object code, which can be  useful  for
                  embedded systems.


                  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(3erl).

                {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(3erl).

                  Warning:  Source  code  can  be  reconstructed  from the debug information. Use
                  encrypted debug information (encrypt_debug_info) to prevent this.



                  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).


                  Similar to the debug_info_key option, but the key is read from an .erlang.crypt

                  For details, see beam_lib(3erl).

                  Omit    the   options   and   source   tuples   in   the   list   returned   by
                  Module:module_info(compile).  This  option  will  make  it  easier  to  achieve
                  reproducible builds.

                  Produces  a  Makefile  rule  to  track  headers dependencies. No object file is

                  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:



                  The Makefile rule generated by this option looks as follows:

                module.beam: module.erl \
                  /usr/local/lib/erlang/lib/eunit/include/eunit.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.

                  Characters in Target special to make(1) are quoted.

                  Considers missing headers as generated files and adds them to the dependencies.

                  Adds a phony target for each dependency.

                  Produces  a  listing  of  the  parsed  code,  after  preprocessing  and   parse
                  transforms, in the file <File>.P. No object file is produced.

                  Produces a listing of the code, after all source code transformations have been
                  performed, in the file <File>.E. No object file is produced.

                  Produces a listing of the assembler code in the file <File>.S. No  object  file
                  is produced.

                  Causes errors/warnings to be printed as they occur.

                  A short form for both report_errors and report_warnings.

                  If  this  flag is set, {error,ErrorList,WarningList} is returned when there are

                  If this flag is set, an extra field, containing WarningList, is  added  to  the
                  tuples returned on success.

                  Causes warnings to be treated as errors. This option is supported since R13B04.

                  A short form for both return_errors and return_warnings.

                  Causes more verbose information from the compiler, describing what it is doing.

                  Sets the value of the source, as returned by module_info(compile).

                  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.

                  Causes all functions in the module to be exported.

                  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


                  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.

                  Causes the parse transformation function Module:parse_transform/2 to be applied
                  to the parsed code before the code is checked for errors.

                  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.

                  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

                  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.

                  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

                {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.

                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:


                  Do not auto-import any functions from erlang module.

                  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 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

                  This option is removed, it generates a fatal error if used.

                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.

                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.

                  Turns off warnings for uses of the export_all option.  Default  is  to  emit  a
                  warning if option export_all is also given.

                  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.

                  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.

                  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.

                  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.

                  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.

                  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.

                  Emits  warnings  for  unused imported functions. Default is to emit no warnings
                  for unused imported functions.

                  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.

                  Turns off warnings for unused record types. Default is  to  emit  warnings  for
                  unused locally defined record types.

                  Turns  off  warnings  for  using  get_stacktrace/0  in  a context where it will
                  probably not work in a future release. For example, by default there will be  a
                  warning if get_stacktrace/0 is used following a catch expression.

              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).

              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.

              The  absence  of  warnings  does not mean that there are no remaining errors in the

              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.

              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

              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:


              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(Forms, Options) -> CompRet


                 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()


                 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


                 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

       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


                 Options = [term()]

              Works   like   output_generated/1,   except   that   the    environment    variable
              ERL_COMPILER_OPTIONS is not consulted.


       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.


       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:


       pi() -> 3.1416.

       Example of implicit inlining:


       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).


       %% Aggressive inlining - will increase code size.


       The  compiler  can also inline various list manipulation functions from the module list in

       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  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.


       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:



       epp(3erl), erl_id_trans(3erl), erl_lint(3erl), beam_lib(3erl)