OCAMLC(1)OCAMLC(1)NAMEocamlc - The OCaml bytecode compiler
SYNOPSISocamlc [ 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 stand‐
alone 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 pro‐
cesses them sequentially:
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 pro‐
duces 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 pro‐
duces 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 byte‐
code 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 link‐
ing 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 inter‐
preter 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 exe‐
cutable 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 mes‐
sages.
-annot Dump detailed information about the compilation (types, bind‐
ings, 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
interactively.
-bin-annot
Dump detailed information about the compilation (types, bind‐
ings, 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 exe‐
cutable file is produced. This option is useful to compile mod‐
ules 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 "cus‐
tom 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.
-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.
-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 run‐
time" mode enables linking OCaml code with user-defined C func‐
tions.
Never use the strip(1) command on executables produced by
ocamlc-custom, this would remove the bytecode part of the exe‐
cutable.
-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 ident
This option is accepted for compatibility with ocamlopt(1) ; it
does nothing.
-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 implemen‐
tation (.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 inter‐
faces, 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 applica‐
tions, 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.
-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.
-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 tradi‐
tion. 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.
-open module
Opens the given module before processing the interface or imple‐
mentation 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 byte‐
code 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 com‐
piled interface (.cmi) that combines the object files given on
the command line, making them appear as sub-modules of the out‐
put .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 compila‐
tion 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 pre‐
processor 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 pro‐
grams accepted in -principal mode are also accepted in the
default mode with equivalent types, but different binary signa‐
tures, 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 depen‐
dencies.
-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 will become the default in a
future version of OCaml.
-short-paths
When a type is visible under several module-paths, use the
shortest one when printing the type's name in inferred inter‐
faces and error and warning messages.
-strict-sequence
Force the left-hand part of each sequence to have type unit.
-thread
Compile or link multithreaded programs, in combination with the
system "threads" library described in The OCaml user's manual.
-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. 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.
-verbose
Print all external commands before they are executed, in partic‐
ular invocations of the C compiler and linker in -custom mode.
Useful to debug C library problems.
-vmthread
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 com‐
piler whenever the source code triggers it. If it is enabled
and fatal, the compiler will also stop with an error after dis‐
playing 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 (inclu‐
sive).
-num1..num2 Disable all warnings between num1 and num2 (inclu‐
sive).
@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 corre‐
sponding 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 com‐
plete 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
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 (_) charac‐
ter.
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 (_) 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 con‐
structor.
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.
The letters stand for the following sets of warnings. Any let‐
ter 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. Note that warn‐
ings 5 and 10 are not always triggered, depending on the inter‐
nals of the type checker.
-warn-error warning-list
Mark as errors the warnings specified in the argument warn‐
ing-list. The compiler will stop with an error when one of
these warnings is emitted. The warning-list has the same mean‐
ing as for the -w option: a + sign (or an uppercase letter)
marks the corresponding warnings as fatal, a - sign (or a lower‐
case 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 com‐
piling your program with later versions of OCaml when they add
new warnings or modify existing warnings.
The default setting is -warn-error -a (all warnings are non-
fatal).
-warn-help
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.
SEE ALSOocamlopt(1), ocamlrun(1), ocaml(1).
The OCaml user's manual, chapter "Batch compilation".
OCAMLC(1)
