OCAMLC(1)                   General Commands Manual                  OCAMLC(1)

       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 x.ml, the ocamlc(1) compiler
       produces compiled object bytecode in the file x.cmo.

       If the interface file x.mli exists, the implementation x.ml is checked
       against the corresponding compiled interface x.cmi, which is assumed to
       exist. If no interface x.mli is provided, the compilation of x.ml
       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 and.ml
       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 below).

       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

              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

       -annot Dump detailed information about the compilation (types,
              bindings, tail-calls, etc).  The information for file src.ml 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

              Dump detailed information about the compilation (types,
              bindings, tail-calls, etc) in binary format. The information for
              file src.ml 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

       -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 program.

       -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) holds.

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

       -error-style mode
              Control the way error messages and warnings are printed.  The
              following modes are supported:

              short only print the error and its location;

              contextual like "short", but also display the source code
              snippet corresponding to the location of the error.

              The default setting is contextual.

              The environment variable "OCAML_ERROR_STYLE" is considered if
              -error-style is not provided. Its values are short/contextual as

              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.

              Print the value of a specific configuration variable from the
              -config output, then exit. If the variable does not exist, the
              exit code is non-zero.

              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

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

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

       -depend ocamldep-args
              Compute dependencies, as ocamldep would do.

       -dllib -llibname
              Arrange for the C shared library dlllibname.so 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 A.ml 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 .ml.

       -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 .mli).

              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.

              Set number of rows of context used during pattern matching
              compilation. Lower values cause faster compilation, but less
              optimized code. The default value is 32.

              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 -I.

       -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

              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.

       -stop-after pass
              Stop compilation after the given compilation pass. The currently
              supported passes are: parsing, typing.

              Enforce the separation between types string and bytes, thereby
              making strings read-only. This is the default.

              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.

              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

              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.  This is intended for compatibility with old source
              code and should not be used with new software.

       -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.

              Deprecated since OCaml 4.08.0. 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 warning-list.

              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

              -num1..num2   Disable all warnings between num1 and num2

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

              +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

              uppercase-letter   Enable the set of warnings corresponding to

              lowercase-letter   Disable the set of warnings corresponding to

              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 ignored.

              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

              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   Deprecated: now part of warning 8.

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

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

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

              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

              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.

              62   Type constraint on GADT type declaration

              63   Erroneous printed signature

              64   -unsafe used with a preprocessor returning a syntax tree

              65   Type declaration defining a new '()' constructor

              66   Unused open! statement.

              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..42-44-45-48-50-60-66.  Note that
              warnings 5 and 10 are not always triggered, depending on the
              internals of the type checker.

       -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

              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

              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 (-)

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

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