OCAMLC(1) User Commands OCAMLC(1)

NAME

ocamlc - The OCaml bytecode compiler

SYNOPSIS

ocamlc [ options ] filename ...

ocamlc.opt [ options ] filename ...

DESCRIPTION

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 x.ml.

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.

OPTIONS

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 Deprecated since 4.11. Please use -bin-annot instead.

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

If -color is not provided, "OCAML_COLOR" is not set and the
environment variable "NO_COLOR" is set, then color output is
disabled. Otherwise, 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.


-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 above.


-compat-32
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.

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

-config-var
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.

-custom
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.

-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-docs
Keep documentation strings in generated .cmi files.

-keep-locs
Keep locations in generated .cmi files.

-labels
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.

-linkall
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.

-make-runtime
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.

-match-context-rows
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.

-no-alias-deps
Do not record dependencies for module aliases.

-no-app-funct
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.

-noassert
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.

-noautolink
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.

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

-nostdlib
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
or -output-complete-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.

-opaque
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.

-output-obj
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).

-output-complete-obj
Same as -output-obj except when creating an object file where
it includes the runtime and autolink libraries.

-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.

-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.

-principal
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.

-rectypes
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
dependencies.

-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.

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

-short-paths
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.

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

-unboxed-types
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].

-no-unboxed-types
When a type is unboxable it will be boxed unless annotated
with [@@ocaml.unboxed]. This is the default.

-unsafe
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.

-unsafe-string
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.

-verbose
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.

-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 fatal or 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 either a mnemonic warning
specifier or a sequence of single character warning
specifiers, with no separators between them. A mnemonic
warning specifier is one of the following

+name Enable warning name.

-name Disable warning name.

@name Enable and mark as fatal warning name.

A single character 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 (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
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 and mnemonic names are as follows.

1 [comment-start]
Suspicious-looking start-of-comment mark.

2 [comment-not-end]
Suspicious-looking end-of-comment mark.

3
Deprecated feature.

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

5 [ignored-partial-application]
Partially applied function: expression whose result has
function type and is ignored.

6 [labels-omitted]
Label omitted in function application.

7 [method-override]
Method overridden without using the "method!" keyword.

8 [partial-match]
Partial match: missing cases in pattern-matching.

9 [missing-record-field-pattern]
Missing fields in a record pattern.

10 [non-unit-statement]
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]
Redundant case in a pattern matching (unused match case).

12 [redundant-subpat]
Redundant sub-pattern in a pattern-matching.

13 [instance-variable-override]
Override of an instance variable.

14 [illegal-backslash]
Illegal backslash escape in a string constant.

15 [implicit-public-methods]
Private method made public implicitly.

16 [unerasable-optional-argument]
Unerasable optional argument.

17 [undeclared-virtual-method]
Undeclared virtual method.

18 [not-principal]
Non-principal type.

19 [non-principal-labels]
Type without principality.

20 [ignored-extra-argument]
Unused function argument.

21 [nonreturning-statement]
Non-returning statement.

22 [preprocessor]
Preprocessor warning.

23 [useless-record-with]
Useless record with clause.

24 [bad-module-name]
Bad module name: the source file name is not a valid OCaml
module name.

25
Deprecated: now part of warning 8.

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

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

28 [wildcard-arg-to-constant-constr]
A pattern contains a constant constructor applied to the
underscore (_) pattern.

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

30 [duplicate-definitions]
Two labels or constructors of the same name are defined in two
mutually recursive types.

31 [module-linked-twice]
A module is linked twice in the same executable.

32 [unused-value-declaration]
Unused value declaration.

33 [unused-open]
Unused open statement.

34 [unused-type-declaration]
Unused type declaration.

35 [unused-for-index]
Unused for-loop index.

36 [unused-ancestor]
Unused ancestor variable.

37 [unused-constructor]
Unused constructor.

38 [unused-extension]
Unused extension constructor.

39 [unused-rec-flag]
Unused rec flag.

40 [name-out-of-scope]
Constructor or label name used out of scope.

41 [ambiguous-name]
Ambiguous constructor or label name.

42 [disambiguated-name]
Disambiguated constructor or label name.

43 [nonoptional-label]
Nonoptional label applied as optional.

44 [open-shadow-identifier]
Open statement shadows an already defined identifier.

45 [open-shadow-label-constructor]
Open statement shadows an already defined label or
constructor.

46 [bad-env-variable]
Error in environment variable.

47 [attribute-payload]
Illegal attribute payload.

48 [eliminated-optional-arguments]
Implicit elimination of optional arguments.

49 [no-cmi-file]
Missing cmi file when looking up module alias.

50 [unexpected-docstring]
Unexpected documentation comment.

51 [wrong-tailcall-expectation]
Function call annotated with an incorrect @tailcall attribute

52 [fragile-literal-pattern]
Fragile constant pattern.

53 [misplaced-attribute]
Attribute cannot appear in this context.

54 [duplicated-attribute]
Attribute used more than once on an expression.

55 [inlining-impossible]
Inlining impossible.

56 [unreachable-case]
Unreachable case in a pattern-matching (based on type
information).

57 [ambiguous-var-in-pattern-guard]
Ambiguous or-pattern variables under guard.

58 [no-cmx-file]
Missing cmx file.


59 [flambda-assignment-to-non-mutable-value]
Assignment on non-mutable value.

60 [unused-module]
Unused module declaration.

61 [unboxable-type-in-prim-decl]
Unannotated unboxable type in primitive declaration.

62 [constraint-on-gadt]
Type constraint on GADT type declaration.

63 [erroneous-printed-signature]
Erroneous printed signature.

64 [unsafe-array-syntax-without-parsing]
-unsafe used with a preprocessor returning a syntax tree.

65 [redefining-unit]
Type declaration defining a new '()' constructor.

66 [unused-open-bang]
Unused open! statement.

67 [unused-functor-parameter]
Unused functor parameter.

68 [match-on-mutable-state-prevent-uncurry]
Pattern-matching depending on mutable state prevents the
remaining arguments from being uncurried.

69 [unused-field]
Unused record field.

70 [missing-mli]
Missing interface file.

71 [unused-tmc-attribute]
Unused @tail_mod_cons attribute

72 [tmc-breaks-tailcall]
A tail call is turned into a non-tail call by the
@tail_mod_cons transformation.


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-4-7-9-27-29-30-32..42-44-45-48-50-60-66..70. 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 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).

-warn-help
Show the description of all available warning numbers.

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

-with-runtime
Include the runtime system in the generated program. This is
the default.

-without-runtime
The compiler does not include the runtime system (nor a
reference to it) in the generated program; it must be supplied
separately.

- 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.

SEE ALSO

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

OCAMLC(1)