# Chapter ‍18 Dependency generator (ocamldep)

- 18.1 Options
- 18.2 A typical Makefile

The ocamldep command scans a set of OCaml source files (.ml and .mli files) for references to external compilation units, and outputs dependency lines in a format suitable for the make utility. This ensures that make will compile the source files in the correct order, and recompile those files that need to when a source file is modified.

The typical usage is:

            ocamldep options *.mli *.ml > .depend

where *.mli *.ml expands to all source files in the current directory and .depend is the file that should contain the dependencies. (See below for a typical Makefile.)

Dependencies are generated both for compiling with the bytecode compiler ocamlc and with the native-code compiler ocamlopt.

## ﻿18.1 Options

The following command-line options are recognized by ocamldep.

-absname
  Show absolute filenames in error messages.
-all
  Generate dependencies on all required files, rather than assuming implicit dependencies.
-allow-approx
  Allow falling back on a lexer-based approximation when parsing fails.
-args filename
  Read additional newline-terminated command line arguments from filename.
-args0 filename
  Read additional null character terminated command line arguments from filename.
-as-map
  For the following files, do not include delayed dependencies for module aliases. This option assumes that they are compiled using options -no-alias-deps -w -49, and that those files or their interface are passed with the -map option when computing dependencies for other files. Note also that for dependencies to be correct in the implementation of a map file, its interface should not coerce any of the aliases it contains.
-debug-map
  Dump the delayed dependency map for each map file.
-I directory
  Add the given directory to the list of directories searched for source files. If a source file foo.ml mentions an external compilation unit Bar, a dependency on that unit’s interface bar.cmi is generated only if the source for bar is found in the current directory or in one of the directories specified with -I. Otherwise, Bar is assumed to be a module from the standard library, and no dependencies are generated. For programs that span multiple directories, it is recommended to pass ocamldep the same -I options that are passed to the compiler.
-nocwd
  Do not add current working directory to the list of include directories.
-impl file
  Process file as a .ml file.
-intf file
  Process file as a .mli file.
-map file
  Read and propagate the delayed dependencies for module aliases in file, so that the following files will depend on the exported aliased modules if they use them. See the example below.
-ml-synonym .ext
  Consider the given extension (with leading dot) to be a synonym for .ml.
-mli-synonym .ext
  Consider the given extension (with leading dot) to be a synonym for .mli.
-modules
  Output raw dependencies of the form

            filename: Module1 Module2 ... ModuleN

  where Module1, …, ModuleN are the names of the compilation units referenced within the file filename, but these names are not resolved to source file names. Such raw dependencies cannot be used by make, but can be post-processed by other tools such as Omake.
-native
  Generate dependencies for a pure native-code program (no bytecode version). When an implementation file (.ml file) has no explicit interface file (.mli file), ocamldep generates dependencies on the bytecode compiled file (.cmo file) to reflect interface changes. This can cause unnecessary bytecode recompilations for programs that are compiled to native-code only. The flag -native causes dependencies on native compiled files (.cmx) to be generated instead of on .cmo files. (This flag makes no difference if all source files have explicit .mli interface files.)
-one-line
  Output one line per file, regardless of the length.
-open module
  Assume that module module is opened before parsing each of the following files.
-pp command
  Cause ocamldep to call the given command as a preprocessor for each source file.
-ppx command
  Pipe abstract syntax trees through preprocessor command.
-shared
  Generate dependencies for native plugin files (.cmxs) in addition to native compiled files (.cmx).
-slash
  Under Windows, use a forward slash (/) as the path separator instead of the usual backward slash (\). Under Unix, this option does nothing.
-sort
  Sort files according to their dependencies.
-version
  Print version string and exit.
-vnum
  Print short version number and exit.
-help or --help
  Display a short usage summary and exit.

## ﻿18.2 A typical Makefile

Here is a template Makefile for a OCaml program.

    OCAMLC=ocamlc
    OCAMLOPT=ocamlopt
    OCAMLDEP=ocamldep
    INCLUDES=                 # all relevant -I options here
    OCAMLFLAGS=$(INCLUDES)    # add other options for ocamlc here
    OCAMLOPTFLAGS=$(INCLUDES) # add other options for ocamlopt here

    # prog1 should be compiled to bytecode, and is composed of three
    # units: mod1, mod2 and mod3.

    # The list of object files for prog1
    PROG1_OBJS=mod1.cmo mod2.cmo mod3.cmo

    prog1: $(PROG1_OBJS)
            $(OCAMLC) -o prog1 $(OCAMLFLAGS) $(PROG1_OBJS)

    # prog2 should be compiled to native-code, and is composed of two
    # units: mod4 and mod5.

    # The list of object files for prog2
    PROG2_OBJS=mod4.cmx mod5.cmx

    prog2: $(PROG2_OBJS)
            $(OCAMLOPT) -o prog2 $(OCAMLFLAGS) $(PROG2_OBJS)

    # Common rules

    %.cmo: %.ml
            $(OCAMLC) $(OCAMLFLAGS) -c $<

    %.cmi: %.mli
            $(OCAMLC) $(OCAMLFLAGS) -c $<

    %.cmx: %.ml
            $(OCAMLOPT) $(OCAMLOPTFLAGS) -c $<

    # Clean up
    clean:
            rm -f prog1 prog2
            rm -f *.cm[iox]

    # Dependencies
    depend:
            $(OCAMLDEP) $(INCLUDES) *.mli *.ml > .depend

    include .depend

If you use module aliases to give shorter names to modules, you need to change the above definitions. Assuming that your map file is called mylib.mli, here are minimal modifications.

    OCAMLFLAGS=$(INCLUDES) -open Mylib

    mylib.cmi: mylib.mli
            $(OCAMLC) $(INCLUDES) -no-alias-deps -w -49 -c $<

    depend:
            $(OCAMLDEP) $(INCLUDES) -map mylib.mli $(PROG1_OBJS:.cmo=.ml) > .depend

Note that in this case you should not compute dependencies for mylib.mli together with the other files, hence the need to pass explicitly the list of files to process. If mylib.mli itself has dependencies, you should compute them using -as-map.