Michael Mera edited this page Nov 17, 2015 · 3 revisions

O'Caml Builder

O'Caml is statically-typed mixed paradigm programming language. Its toolchain functions somewhat differently from that of gcc, and it's currently unsupported by SCons. Since I'd like to use SCons to build an O'Caml project, I'm adding the necessary code.

Please note that I'm a novice when it comes to SCons, so if you can improve something on this page, please do!

Russel Winder has created a Bazaar branch of a SCons OCaml tool based on this code. It can be found at https://bitbucket.org/russel/scons_ocaml


Let's have a closer look at the tools provided by the O'Caml distribution:

Tool Description
ocaml a interactive bytecode interpreter
ocamlc a bytecode compiler
ocamlopt a native code compiler
ocamlfind an environment querying tool
ocamldep a utility for determining build dependencies
ocamldoc a utility for generating documentation embedded in source code
ocamlmktop Building custom toplevel systems
ocamlyacc Ocaml Yacc
ocamllex Ocaml Lex
ocamlmklib generate libraries with mixed C / Caml code


Extension Description
.ml a source file
.mli a module interface file
.cmi a compiled interface
.cmo a bytecode compiled object
.cma a bytecode library
.cmx a native compiled object
.cmxa a native library
.mll Ocaml Lex file
.mly Ocaml Yacc file

ocamlc generates .cmi files from .mli files, and .cmo files from .ml files

ocamlopt generates .cmi files from .mli files and .cmx and .o files from .ml files


O'Caml modules are opened using the syntax:

open ModuleName

The above is O’Caml’s equivalent to Python’s from ModuleName import *. The scanner below won’t find dependencies on modules that aren’t open’ed, such as just using the module name. For instance, to use the map function from the List module, you just say List.map, and you don’t need to mention List anywhere else. You’ll need to use the ocamldep command to get the dependencies, in general.

Here's a scanner:

# use re.MULTILINE flag, so '^' matches at the beginning of the
# string and at the beginning of each line, i.e. after each newline.
# Matching of '$' is similary affected.
open_re = re.compile('^open\\s+(\\S+)$', re.MULTILINE)
def scan_ml_for_deps(node):
  contents = node.get_contents()
  found = open_re.findall(contents)
  return map(str.lower, found)
# Bytecode
def mlfile_scan_bytecode(node, env, path):
  found = scan_ml_for_deps(node)
  bytecode_objects = map(lambda x: x + '.cmo', found)
  return bytecode_objects
mlscan_bytecode = Scanner(function = mlfile_scan_bytecode, skeys = ['.ml'])

Ocaml Tool

This tool provides four builders:

  • OcamlObject
  • OcamlLibrary
  • OcamlProgram
  • OcamlPack

which works like Object, Library and Program. You can customize command line options and choose between a bytecode executable, a native one or a toplevel (interactive loop).

OcamlPack is used for packing several object into one (see option -pack of ocamlc).

Ocaml Tool file:

# Ocaml Tool
# version: 0.2 (12/30/2005)
# - testing
# - make it portable (currently only tested on Unix)
# - Lex and Yacc builders
import os
def read_command(cmd):
        Execute the command cmd and return output
        return os.popen(cmd).readlines()
def when_code(env, bytecode, native, toplevel=None):
        Return value depending on output code kind wanted
        if toplevel == None:
                toplevel = bytecode
        if env['OCAML_CODE'] == 'bytecode':
                r = bytecode
        elif env['OCAML_CODE'] == 'native':
                r = native
        elif env['OCAML_CODE'] == 'toplevel':
                r = toplevel
                print "$OCAML_CODE must be either 'toplevel', 'bytecode' or 'native'"
        return r
def obj_suffix(env):
        return when_code(env, '.cmo', '.cmx')
def lib_suffix(env):
        return when_code(env, '.cma', '.cmxa')
def set_suffix(f, suffix):
        b, e = os.path.splitext(str(f))
        return b+suffix
def obj_of_src(f, env):
        return set_suffix(f, obj_suffix(env))
def iface_of_src(f):
        return set_suffix(f, '.cmi')
def comp(env):
        Choose a compiler depending on environment variables
        return when_code(env, '$OCAMLC', '$OCAMLOPT', '$OCAMLMKTOP')
def flags(env, t=''):
        Generate flags depending on environment variables
        s = when_code(env, '$OCAMLC_FLAGS', '$OCAMLOPT_FLAGS', '$OCAMLMKTOP_FLAGS')
        if env['OCAML_DEBUG']:
                s += when_code(env, ' -g', '')
        if env['OCAML_PROFILE']:
                s += when_code(env, '', ' -p')
        if env['OCAML_PP']:
                s += ' -pp %s' % env['OCAML_PP']
        if t == 'lib':
                s += ' -a'
        elif t == 'obj':
                s += ' -c'
        elif t == 'pack':
                s += ' -pack'
        return s
def is_installed(exe):
        Return True if an executable is found in path
        path = os.environ['PATH'].split(':')
        for p in path:
                if os.path.exists( os.path.join(p, exe) ):
                        return True
        return False
def norm_suffix(f, suffix):
        Add a suffix if not present
        p = str(f)
        e = p[-len(suffix):]
        if e != suffix:
                p = p + suffix
        return p
def norm_suffix_list(files, suffix):
        return map(lambda x: norm_suffix(x, suffix), files)
def find_packages(env):
        Use ocamlfind to retrieve libraries paths from package names
        packs = env.Split(env['OCAML_PACKS'])
        if not is_installed(env['OCAMLFIND']):
                if len(packs):
                        print "Warning: ocamlfind not found, ignoring ocaml packages"
                return ""
        s = "%s query %%s -separator ' ' %s" % (
                env['OCAMLFIND'], " ".join( packs)
        i = read_command(s % '-i-format')
        l = read_command(s % '-l-format')
        code = when_code(env, 'byte', 'native')
        a = read_command(s % '-predicates %s -a-format' % code)
        r = " %s %s %s " % ( l[0][:-1], i[0][:-1], a[0][:-1] )
        return r
def cleaner(files, env, lib=False):
        files = map(str, files)
        r = []
        for f in files:
                r.append(obj_of_src(f, env))
                if env['OCAML_CODE'] == 'native':
                        r.append(set_suffix(f, '.o'))
                        if lib:
                                r.append(set_suffix(f, '.a'))
        return r
def scanner(node, env, path):
        objs = norm_suffix_list(env['OCAML_OBJS'], obj_suffix(env))
        libs = norm_suffix_list(env['OCAML_LIBS'], lib_suffix(env))
        return libs+objs
prog_scanner = lib_scanner = obj_scanner = pack_scanner = scanner
def lib_emitter(target, source, env):
        t = norm_suffix(str(target[0]), lib_suffix(env))
        env.Clean(t, cleaner(source, env, lib=True))
        return (t, source)
def obj_emitter(target, source, env):
        t = norm_suffix(str(target[0]), obj_suffix(env))
        env.Clean(t, cleaner(source+[t], env))
        return (t, source)
def pack_emitter(target, source, env):
        t = norm_suffix(str(target[0]), obj_suffix(env))
        s = norm_suffix_list(source, obj_suffix(env))
        env.Clean(t, cleaner(source+[t], env))
        return (t, source)
def prog_emitter(target, source, env):
        env.Clean(target, cleaner(source, env))
        return (target, source)
def command_gen(source, target, env, comp, flags):
        Generate command
        target = str(target[0])
        objs = norm_suffix_list(env['OCAML_OBJS'], obj_suffix(env))
        objs = " ".join( objs )
        libs = norm_suffix_list(env['OCAML_LIBS'], lib_suffix(env))
        libs = " ".join( libs )
        inc = map(lambda x:'-I '+x, env['OCAML_PATH'])
        inc = " ".join(inc) + find_packages(env)
        s = ("%s %s -o %s %s %s %s $SOURCES" %
                        (comp, flags, target, inc, libs, objs)
        return s
def obj_gen(source, target, env, for_signature):
        return command_gen( source, target, env, comp(env), flags(env, 'obj'))
def pack_gen(source, target, env, for_signature):
        return command_gen(source, target, env, comp(env), flags(env, 'pack'))
def lib_gen(source, target, env, for_signature):
        return command_gen( source, target, env, comp(env), flags(env, 'lib'))
def prog_gen(source, target, env, for_signature):
        return command_gen(source, target, env, comp(env), flags(env))
def generate(env):
        Add Builders and construction variables for Ocaml to an Environment.
        prog_scan = env.Scanner(prog_scanner)
        lib_scan = env.Scanner(lib_scanner)
        obj_scan = env.Scanner(obj_scanner)
        pack_scan = env.Scanner(pack_scanner)
        env.Append(BUILDERS = {
                'OcamlObject': env.Builder(
                # Pack several object into one object file
                'OcamlPack': env.Builder(
                'OcamlLibrary': env.Builder(
                'OcamlProgram': env.Builder(
                #OCAMLDEP='ocamldep',           # not used
                OCAML_PP='',                    # not needed by default
                OCAML_CODE=''                   # bytecode, toplevel or native
def exists(env):
        return env.Detect('ocaml')


There are three files: lib.ml, object.ml and prog.ml, we want to build the executable prog.

The dependencies are:

  • prog: object.cmx lib.cmxa prog.ml
  • object.cmx: object.ml lib.cmxa
  • lib.cmxa: lib.ml
(* lib.ml *)
print_endline "lib.ml"
(* object.ml *)
open Lib;;
print_endline "object.ml"
(* prog.ml *)
open Graph.Builder;;
open Object;;
print_endline "hello ocaml world !";;

The SConstruct file:

# SConstruct
import ocaml
env = Environment(
        OCAML_CODE='native',       # could be 'bytecode'

env.Tool('ocaml', '.')
o = env.OcamlObject('object', 'object.ml')
l = env.OcamlLibrary('lib', 'lib.ml')
env.OcamlProgram('prog', 'prog.ml', OCAML_LIBS=l, OCAML_OBJS=o)

This is the building process:

$ ls
lib.ml  object.ml  ocaml.py  ocaml.pyc  prog.ml  SConstruct
$ scons prog
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
ocamlopt -a -o lib.cmxa -ccopt -L/usr/lib/ocaml/3.08.3/ocamlgraph -I /usr/lib/ocaml/3.08.3/ocamlgraph lib.ml
ocamlopt -c -o object.cmx -ccopt -L/usr/lib/ocaml/3.08.3/ocamlgraph -I /usr/lib/ocaml/3.08.3/ocamlgraph object.ml
ocamlopt -o prog -ccopt -L/usr/lib/ocaml/3.08.3/ocamlgraph -I /usr/lib/ocaml/3.08.3/ocamlgraph lib.cmxa object.cmx prog.ml
scons: done building targets.

$ ls
lib.a    lib.cmxa  object.cmi  object.o   prog      prog.ml
lib.cmi  lib.ml    object.cmx  ocaml.py   prog.cmi  prog.o
lib.cmx  lib.o     object.ml   ocaml.pyc  prog.cmx  SConstruct

$ scons -c
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Cleaning targets ...
Removed lib.cmxa
Removed lib.cmx
Removed lib.cmi
Removed lib.o
Removed lib.a
Removed object.cmx
Removed object.cmi
Removed object.o
Removed prog
Removed prog.cmx
Removed prog.cmi
Removed prog.o
scons: done cleaning targets.
$ ./prog
hello ocaml world !
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