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       ocamlc - The OCaml bytecode compiler


       ocamlc [ options ] filename ...

       ocamlc.opt [ options ] filename ...


       The OCaml bytecode compiler ocamlc(1) compiles OCaml source files to bytecode object files
       and links these object files to  produce  standalone  bytecode  executable  files.   These
       executable files are then run by the bytecode interpreter ocamlrun(1).

       The ocamlc(1) command has a command-line interface similar to the one of most C compilers.
       It accepts several types of arguments and processes them sequentially, after  all  options
       have been processed:

       Arguments  ending  in  .mli  are taken to be source files for compilation unit interfaces.
       Interfaces specify the names exported by compilation units: they declare value names  with
       their  types,  define  public data types, declare abstract data types, and so on. From the
       file x.mli, the ocamlc(1) compiler produces a compiled interface in the file x.cmi.

       Arguments ending in .ml are taken to be source files for compilation unit implementations.
       Implementations  provide  definitions for the names exported by the unit, and also contain
       expressions to be evaluated for their side-effects.  From the  file,  the  ocamlc(1)
       compiler produces compiled object bytecode in the file x.cmo.

       If  the  interface  file  x.mli  exists,  the  implementation is checked against the
       corresponding compiled interface x.cmi, which is assumed to exist. If no  interface  x.mli
       is  provided, the compilation of produces a compiled interface file x.cmi in addition
       to the compiled object code file  x.cmo.   The  file  x.cmi  produced  corresponds  to  an
       interface that exports everything that is defined in the implementation

       Arguments ending in .cmo are taken to be compiled object bytecode.  These files are linked
       together, along with the object files obtained by compiling .ml arguments  (if  any),  and
       the OCaml standard library, to produce a standalone executable program. The order in which
       .cmo arguments are presented on the command line is relevant: compilation units are
       initialized in that order at run-time, and it is a link-time error to use a component of a
       unit before having initialized it. Hence, a given x.cmo file must  come  before  all  .cmo
       files that refer to the unit x.

       Arguments  ending  in  .cma  are  taken  to be libraries of object bytecode.  A library of
       object bytecode packs in a single file a  set  of  object  bytecode  files  (.cmo  files).
       Libraries  are  built  with  ocamlc -a  (see  the description of the -a option below). The
       object files contained in the library are linked as regular .cmo files (see above), in the
       order  specified  when  the  .cma file was built. The only difference is that if an object
       file contained in a library is not referenced anywhere in the  program,  then  it  is  not
       linked in.

       Arguments  ending  in  .c  are passed to the C compiler, which generates a .o object file.
       This object file is linked  with  the  program  if  the  -custom  flag  is  set  (see  the
       description of -custom below).

       Arguments  ending  in  .o  or  .a are assumed to be C object files and libraries. They are
       passed to the C linker when linking in  -custom  mode  (see  the  description  of  -custom

       Arguments ending in .so are assumed to be C shared libraries (DLLs).  During linking, they
       are searched for external C functions referenced from the OCaml code, and their names  are
       written  in the generated bytecode executable.  The run-time system ocamlrun(1) then loads
       them dynamically at program start-up time.

       The output of the linking phase is  a  file  containing  compiled  bytecode  that  can  be
       executed  by  the OCaml bytecode interpreter: the command ocamlrun(1).  If caml.out is the
       name  of  the  file  produced  by  the  linking  phase,  the  command  ocamlrun   caml.out
       arg1  arg2 ... argn  executes  the  compiled  code  contained  in  caml.out, passing it as
       arguments the character strings arg1 to argn.  (See ocamlrun(1) for more details.)

       On most systems, the file produced by the linking  phase  can  be  run  directly,  as  in:
       ./caml.out  arg1  arg2 ... argn.   The  produced  file  has the executable bit set, and it
       manages to launch the bytecode interpreter by itself.

       ocamlc.opt is the same compiler as ocamlc, but  compiled  with  the  native-code  compiler
       ocamlopt(1).   Thus,  it behaves exactly like ocamlc, but compiles faster.  ocamlc.opt may
       not be available in all installations of OCaml.


       The following command-line options are recognized by ocamlc(1).

       -a     Build a library (.cma file) with the object files (.cmo files) given on the command
              line, instead of linking them into an executable file. The name of the library must
              be set with the -o option.

              If -custom, -cclib or -ccopt options are passed on the command line, these  options
              are  stored  in  the  resulting  .cma  library.   Then,  linking  with this library
              automatically adds back the -custom, -cclib and -ccopt options as if they had  been
              provided on the command line, unless the -noautolink option is given. Additionally,
              a substring $CAMLORIGIN inside a  -ccopt options will be replaced by the full  path
              to  the  .cma library, excluding the filename.  -absname Show absolute filenames in
              error messages.

       -annot Dump detailed information about the compilation (types, bindings, tail-calls, etc).
              The  information  for  file  is put into file src.annot.  In case of a type
              error, dump all the information inferred by the type-checker before the error.  The
              src.annot  file can be used with the emacs commands given in emacs/caml-types.el to
              display types and other annotations interactively.

              Dump detailed information about the compilation (types, bindings, tail-calls,  etc)
              in  binary  format.  The  information for file is put into file src.cmt.  In
              case of a type error, dump all the information inferred by the type-checker  before
              the  error.   The  annotation files produced by -bin-annot contain more information
              and are much more compact than the files produced by -annot.

       -c     Compile only. Suppress the linking phase of the compilation. Source code files  are
              turned  into  compiled  files,  but  no executable file is produced. This option is
              useful to compile modules separately.

       -cc ccomp
              Use ccomp as the C linker when linking in "custom runtime" mode  (see  the  -custom
              option) and as the C compiler for compiling .c source files.

       -cclib -llibname
              Pass  the  -llibname  option  to the C linker when linking in "custom runtime" mode
              (see the -custom option). This causes the given C library to  be  linked  with  the

       -ccopt option
              Pass  the  given  option  to  the  C  compiler  and linker, when linking in "custom
              runtime" mode (see the -custom option). For instance,  -ccopt -Ldir  causes  the  C
              linker to search for C libraries in directory dir.

       -color mode
              Enable  or  disable  colors  in compiler messages (especially warnings and errors).
              The following modes are supported:

              auto use heuristics to enable colors only if the output  supports  them  (an  ANSI-
              compatible tty terminal);

              always enable colors unconditionally;

              never disable color output.

              The  default  setting  is  auto,  and  the current heuristic checks that the "TERM"
              environment variable exists and is not empty or  "dumb",  and  that  isatty(stderr)

              The environment variable "OCAML_COLOR" is considered if -color is not provided. Its
              values are auto/always/never as above.

              Check that the generated bytecode executable can run on 32-bit platforms and signal
              an error if it cannot. This is useful when compiling bytecode on a 64-bit machine.

              Print  the version number of ocamlc(1) and a detailed summary of its configuration,
              then exit.

              Link in "custom runtime" mode. In the default linking  mode,  the  linker  produces
              bytecode  that  is  intended  to  be  executed  with  the  shared  runtime  system,
              ocamlrun(1).  In the custom runtime mode, the linker produces an output  file  that
              contains  both  the  runtime system and the bytecode for the program. The resulting
              file is larger, but it can be executed directly, even if the ocamlrun(1) command is
              not  installed. Moreover, the "custom runtime" mode enables linking OCaml code with
              user-defined C functions.

              Never use the strip(1) command on  executables  produced  by  ocamlc -custom,  this
              would remove the bytecode part of the executable.

              Security  warning:  never set the "setuid" or "setgid" bits on executables produced
              by ocamlc -custom, this would make them vulnerable to attacks.

       -dllib -llibname
              Arrange for the C shared library to be loaded dynamically by the run-
              time system ocamlrun(1) at program start-up time.

       -dllpath dir
              Adds  the  directory  dir  to  the run-time search path for shared C libraries.  At
              link-time, shared libraries are searched in  the  standard  search  path  (the  one
              corresponding  to  the  -I  option).   The -dllpath option simply stores dir in the
              produced executable file, where ocamlrun(1) can find it and use it.

       -for-pack module-path
              Generate an object file (.cmo file) that can later  be  included  as  a  sub-module
              (with  the  given  access  path) of a compilation unit constructed with -pack.  For
              instance, ocamlc -for-pack P -c will generate a.cmo that  can  later  be  used
              with  ocamlc  -pack  -o  P.cmo  a.cmo.   Note: you can still pack a module that was
              compiled without -for-pack but in this case exceptions will  be  printed  with  the
              wrong names.

       -g     Add  debugging  information while compiling and linking. This option is required in
              order to be able to debug the program  with  ocamldebug(1)  and  to  produce  stack
              backtraces when the program terminates on an uncaught exception.

       -i     Cause  the  compiler to print all defined names (with their inferred types or their
              definitions) when compiling an implementation (.ml file). No compiled  files  (.cmo
              and  .cmi  files)  are produced.  This can be useful to check the types inferred by
              the compiler. Also, since the output follows the syntax of interfaces, it can  help
              in writing an explicit interface (.mli file) for a file: just redirect the standard
              output of the  compiler  to  a  .mli  file,  and  edit  that  file  to  remove  all
              declarations of unexported names.

       -I directory
              Add  the given directory to the list of directories searched for compiled interface
              files (.cmi), compiled object code files (.cmo), libraries (.cma), and C  libraries
              specified with -cclib -lxxx .  By default, the current directory is searched first,
              then the standard library directory. Directories added with -I are  searched  after
              the  current  directory, in the order in which they were given on the command line,
              but before the standard library directory. See also option -nostdlib.

              If the given directory starts with +, it is taken relative to the standard  library
              directory.  For  instance, -I +compiler-libs adds the subdirectory compiler-libs of
              the standard library to the search path.

       -impl filename
              Compile the file filename as an implementation file, even if its extension  is  not

       -intf filename
              Compile the file filename as an interface file, even if its extension is not .mli.

       -intf-suffix string
              Recognize  file names ending with string as interface files (instead of the default

              Keep documentation strings in generated .cmi files.

              Keep locations in generated .cmi files.

              Labels are not ignored in types, labels may be used in applications,  and  labelled
              parameters can be given in any order.  This is the default.

              Force  all  modules  contained  in  libraries  to be linked in. If this flag is not
              given, unreferenced modules are not linked in. When building a library (option -a),
              setting  the -linkall option forces all subsequent links of programs involving that
              library to link all the modules contained in the library.  When compiling a  module
              (option  -c),  setting  the -linkall option ensures that this module will always be
              linked if it is put in a library and this library is linked.

              Build a custom runtime system (in the file specified by  option  -o)  incorporating
              the  C  object  files and libraries given on the command line.  This custom runtime
              system can be used later to execute bytecode executables produced with  the  option
              ocamlc -use-runtime runtime-name.

              Do not record dependencies for module aliases.

              Deactivates  the  applicative behaviour of functors. With this option, each functor
              application generates new types in its result and applying the same  functor  twice
              to the same argument yields two incompatible structures.

              Do not compile assertion checks.  Note that the special form assert false is always
              compiled because it is typed specially.  This  flag  has  no  effect  when  linking
              already-compiled files.

              When  linking .cma libraries, ignore -custom, -cclib and -ccopt options potentially
              contained in  the  libraries  (if  these  options  were  given  when  building  the
              libraries).  This can be useful if a library contains incorrect specifications of C
              libraries or C options; in this case, during linking, set -noautolink and pass  the
              correct C libraries and options on the command line.

              Ignore  non-optional  labels  in  types. Labels cannot be used in applications, and
              parameter order becomes strict.

              Do not automatically add the standard library directory to the list of  directories
              searched  for  compiled  interface files (.cmi), compiled object code files (.cmo),
              libraries (.cma), and C libraries specified with -cclib -lxxx .   See  also  option

       -o exec-file
              Specify the name of the output file produced by the linker. The default output name
              is a.out, in keeping with the Unix tradition. If the -a option  is  given,  specify
              the  name  of the library produced.  If the -pack option is given, specify the name
              of the packed object file produced.  If the -output-obj option  is  given,  specify
              the  name  of  the  output  file produced.  This can also be used when compiling an
              interface or implementation file, without linking, in which case it sets  the  name
              of  the  cmi  or cmo file, and also sets the module name to the file name up to the
              first dot.

              Interface file compiled with this option are marked so that other compilation units
              depending  on  it  will  not  rely  on  any  implementation details of the compiled
              implementation. The native compiler will not access the .cmx file of this  unit  --
              nor  warn  if it is absent. This can improve speed of compilation, for both initial
              and incremental builds, at the expense of performance of the generated code.

       -open module
              Opens the given module before processing the interface or implementation files.  If
              several  -open  options  are  given,  they  are  processed in order, just as if the
              statements open! module1;; ... open! moduleN;; were added at the top of each file.

              Cause the linker to produce a C object file instead of a bytecode executable  file.
              This  is useful to wrap OCaml code as a C library, callable from any C program. The
              name of the output object file must be set with the -o option. This option can also
              be  used  to  produce  a  C source file (.c extension) or a compiled shared/dynamic
              library (.so extension).

       -pack  Build a bytecode object file (.cmo file)  and  its  associated  compiled  interface
              (.cmi) that combines the object files given on the command line, making them appear
              as sub-modules of the output .cmo file.  The name of the output .cmo file  must  be
              given  with  the  -o option.  For instance, ocamlc -pack -o p.cmo a.cmo b.cmo c.cmo
              generates compiled files p.cmo and p.cmi describing a compilation unit having three
              sub-modules  A,  B  and C, corresponding to the contents of the object files a.cmo,
              b.cmo and c.cmo.  These contents can be referenced as  P.A,  P.B  and  P.C  in  the
              remainder of the program.

       -plugin plugin
              Dynamically  load  the code of the given plugin (a .cmo, .cma or .cmxs file) in the
              compiler. The plugin  must  exist  in  the  same  kind  of  code  as  the  compiler
              (ocamlc.byte  must  load  bytecode  plugins, while ocamlc.opt must load native code
              plugins), and extension adaptation is done automatically for .cma files  (to  .cmxs
              files if the compiler is compiled in native code).

       -pp command
              Cause  the  compiler  to  call  the given command as a preprocessor for each source
              file. The output of command  is  redirected  to  an  intermediate  file,  which  is
              compiled.  If  there  are  no  compilation errors, the intermediate file is deleted
              afterwards. The name of this file is built from the basename  of  the  source  file
              with the extension .ppi for an interface (.mli) file and .ppo for an implementation
              (.ml) file.

       -ppx command
              After parsing, pipe the abstract syntax tree through the preprocessor command.  The
              module Ast_mapper(3) implements the external interface of a preprocessor.

              Check  information  path  during  type-checking,  to  make  sure that all types are
              derived in a principal way.   When  using  labelled  arguments  and/or  polymorphic
              methods,  this  flag  is required to ensure future versions of the compiler will be
              able to infer types correctly, even if internal algorithms  change.   All  programs
              accepted  in  -principal mode are also accepted in the default mode with equivalent
              types, but different binary signatures, and this may slow down type  checking;  yet
              it is a good idea to use it once before publishing source code.

              Allow  arbitrary  recursive types during type-checking.  By default, only recursive
              types where the recursion goes through an object type are supported. Note that once
              you  have  created  an  interface  using  this  flag, you must use it again for all

       -runtime-variant suffix
              Add suffix to the name of the runtime library that will be used by the program.  If
              OCaml  was  configured  with  option  -with-debug-runtime,  then  the  d  suffix is
              supported and gives a debug version of the runtime.

              Enforce the separation between types string and bytes, thereby making strings read-
              only. This will become the default in a future version of OCaml.

              When  a  type  is  visible  under  several  module-paths, use the shortest one when
              printing the type's name in inferred interfaces and error and warning messages.

              Force the left-hand part of each sequence to have type unit.

              Compile or link multithreaded programs, in combination with  the  system  "threads"
              library described in The OCaml user's manual.

              When  a  type  is  unboxable  (i.e.  a  record with a single argument or a concrete
              datatype with a single constructor of one  argument)  it  will  be  unboxed  unless
              annotated with [@@ocaml.boxed].

              When a type is unboxable  it will be boxed unless annotated with [@@ocaml.unboxed].
              This is the default.

              Turn  bound  checking  off  for  array  and  string  accesses  (the   v.(i)ands.[i]
              constructs).  Programs  compiled  with  -unsafe  are therefore slightly faster, but
              unsafe: anything can happen if the program accesses an array or string  outside  of
              its bounds.

              Identify  the  types string and bytes, thereby making strings writable. For reasons
              of backward compatibility, this is the default setting for  the  moment,  but  this
              will change in a future version of OCaml.

       -use-runtime runtime-name
              Generate  a  bytecode  executable  file  that can be executed on the custom runtime
              system runtime-name, built earlier with ocamlc -make-runtime runtime-name.

       -v     Print the version number of the compiler and the location of the  standard  library
              directory, then exit.

              Print  all external commands before they are executed, in particular invocations of
              the C compiler and linker in -custom mode.  Useful to debug C library problems.

              Compile or link multithreaded programs, in combination with  the  VM-level  threads
              library described in The OCaml user's manual.

       -vnum or -version
              Print the version number of the compiler in short form (e.g. "3.11.0"), then exit.

       -w warning-list
              Enable,  disable,  or  mark  as  fatal  the  warnings  specified  by  the  argument

              Each warning can be enabled or disabled, and each warning can be fatalor non-fatal.
              If  a warning is disabled, it isn't displayed and doesn't affect compilation in any
              way (even if it is fatal).  If a warning is enabled, it is  displayed  normally  by
              the compiler whenever the source code triggers it.  If it is enabled and fatal, the
              compiler will also stop with an error after displaying it.

              The warning-list argument is a sequence of warning specifiers, with  no  separators
              between them.  A warning specifier is one of the following:

              +num   Enable warning number num.

              -num   Disable warning number num.

              @num   Enable and mark as fatal warning number num.

              +num1..num2   Enable all warnings between num1 and num2 (inclusive).

              -num1..num2   Disable all warnings between num1 and num2 (inclusive).

              @num1..num2    Enable  and  mark  as  fatal  all  warnings  between  num1  and num2

              +letter   Enable the set of warnings corresponding to letter.  The  letter  may  be
              uppercase or lowercase.

              -letter    Disable  the set of warnings corresponding to letter.  The letter may be
              uppercase or lowercase.

              @letter   Enable and mark as fatal the set of  warnings  corresponding  to  letter.
              The letter may be uppercase or lowercase.

              uppercase-letter   Enable the set of warnings corresponding to uppercase-letter.

              lowercase-letter   Disable the set of warnings corresponding to lowercase-letter.

              The warning numbers are as follows.

              1    Suspicious-looking start-of-comment mark.

              2    Suspicious-looking end-of-comment mark.

              3    Deprecated feature.

              4     Fragile  pattern  matching:  matching  that  will  remain  complete  even  if
              additional constructors are added to one of the variant types matched.

              5    Partially applied function: expression whose result has function type  and  is

              6    Label omitted in function application.

              7    Method overridden without using the "method!" keyword

              8    Partial match: missing cases in pattern-matching.

              9    Missing fields in a record pattern.

              10    Expression  on  the  left-hand side of a sequence that doesn't have type unit
              (and that is not a function, see warning number 5).

              11   Redundant case in a pattern matching (unused match case).

              12   Redundant sub-pattern in a pattern-matching.

              13   Override of an instance variable.

              14   Illegal backslash escape in a string constant.

              15   Private method made public implicitly.

              16   Unerasable optional argument.

              17   Undeclared virtual method.

              18   Non-principal type.

              19   Type without principality.

              20   Unused function argument.

              21   Non-returning statement.

              22   Preprocessor warning.

              23   Useless record with clause.

              24   Bad module name: the source file name is not a valid OCaml module name.

              25   Pattern-matching with all clauses guarded.

              26   Suspicious unused variable: unused variable that is bound with let or as,  and
              doesn't start with an underscore (_) character.

              27    Innocuous unused variable: unused variable that is not bound with let nor as,
              and doesn't start with an underscore (_) character.

              28   A pattern contains a  constant  constructor  applied  to  the  underscore  (_)

              29    A  non-escaped  end-of-line  was  found in a string constant.  This may cause
              portability problems between Unix and Windows.

              30   Two labels or constructors of the  same  name  are  defined  in  two  mutually
              recursive types.

              31   A module is linked twice in the same executable.

              32   Unused value declaration.

              33   Unused open statement.

              34   Unused type declaration.

              35   Unused for-loop index.

              36   Unused ancestor variable.

              37   Unused constructor.

              38   Unused extension constructor.

              39   Unused rec flag.

              40   Constructor or label name used out of scope.

              41   Ambiguous constructor or label name.

              42   Disambiguated constructor or label name.

              43   Nonoptional label applied as optional.

              44   Open statement shadows an already defined identifier.

              45   Open statement shadows an already defined label or constructor.

              46   Error in environment variable.

              47   Illegal attribute payload.

              48   Implicit elimination of optional arguments.

              49   Missing cmi file when looking up module alias.

              50   Unexpected documentation comment.

              59   Assignment on non-mutable value.

              60   Unused module declaration.

              61   Unannotated unboxable type in primitive declaration.

              The  letters  stand  for  the following sets of warnings.  Any letter not mentioned
              here corresponds to the empty set.

              A  all warnings

              C  1, 2

              D  3

              E  4

              F  5

              K  32, 33, 34, 35, 36, 37, 38, 39

              L  6

              M  7

              P  8

              R  9

              S  10

              U  11, 12

              V  13

              X  14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 30

              Y  26

              Z  27

              The default setting is -w +a-4-6-7-9-27-29-32..39-41-42-44-45-48-50-60.  Note  that
              warnings  5 and 10 are not always triggered, depending on the internals of the type

       -warn-error warning-list
              Mark as errors the warnings specified in the argument warning-list.   The  compiler
              will  stop  with  an error when one of these warnings is emitted.  The warning-list
              has the same meaning as for the -w option: a + sign (or an uppercase letter)  marks
              the  corresponding  warnings  as fatal, a - sign (or a lowercase letter) turns them
              back into non-fatal warnings, and a @ sign both enables  and  marks  as  fatal  the
              corresponding warnings.

              Note:  it  is  not  recommended  to  use the -warn-error option in production code,
              because it will almost certainly prevent compiling your program with later versions
              of OCaml when they add new warnings or modify existing warnings.

              The default setting is -warn-error -a+31 (only warning 31 is fatal).

              Show the description of all available warning numbers.

       -where Print the location of the standard library, then exit.

       - file Process file as a file name, even if it starts with a dash (-) character.

       -help or --help
              Display a short usage summary and exit.


       ocamlopt(1), ocamlrun(1), ocaml(1).
       The OCaml user's manual, chapter "Batch compilation".