Ubuntu Manpage: ocamlc - The OCaml bytecode compiler

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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.

-no-absname
Do not try to 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.

-no-g Do not record debugging information (default).

-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.

-cmi-file filename
Type-check the source implementation to be compiled against the specified interface file (by-
passes the normal lookup for .mli and .cmi files).

-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.

-no-principal
Do not check principality of type inference. This is the default.

-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.

-no-rectypes
Do no allow arbitrary recursive types during type-checking. This is the default.

-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.

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

-safer-matching
Do not use type information to optimize pattern-matching. This allows to detect match failures
even if a pattern-matching was wrongly assumed to be exhaustive. This only impacts GADT and
polymorphic variant compilation.

-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.

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

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

-no-strict-sequence
Left-hand part of a sequence need not have type unit. This is the default.

-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) and s.[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.

73 [generative-application-expects-unit]
A generative functor is applied to an empty structure (struct end) rather than to ().

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 (no warning 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.

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

SEE ALSO