OCaml: Toolchains & Ecosystem Last updated May 16, 2022

Status: very rough as of 5/25/22.

Standard OCaml distributions contain no fewer than four toolchains. …​

The current OBazl toolsuite uses one OPAM-based Bazel toolchain that contains all the tools in the selected OPAM switch (i.e. OCaml distribution). Build mode (bytecode or native) is controlled by a configurable default rule passed on the command line; see X for details. The profiling compilers are not supported. The next version will contain one Bazel toolchain for each OCaml toolchain.

Compilers

bytecode binaries native binaries remarks

emit bytecode:

ocamlc.byte

ocamlc.opt

std compilers

ocamlcp.byte

ocamlcp.opt

profiling compilers

emit native code:

ocamlopt.byte

ocamlopt.opt

std compilers

ocamloptp.byte

ocamloptp.opt

profiling compilers
These are all utility commands. The actually compilers are implemented as libraries; these commands are actually drivers, like the gcc command of the GNU toolchain. They run the compilers but may also run other tools.

The *.opt versions are native code binaries; the *.byte versions are bytecode binaries, which must be executed with ocamlrun.

The profiling complers instrument the source code, adding code to record how many times functions are called, branches of conditionals are taken, etc. See also Runtime tracing with the instrumented runtime.

By default, names without an extension are symlinked to the optimized (native) binaries:

  • ocamlc → ocamlc.opt

  • ocamlcp → ocamlcp.opt

  • ocamlopt → ocamlopt.opt

  • ocamloptp → ocamloptp.opt

By default, the OBazl rules use ocamlopt.opt: the native-code compiler binary that emits native code.

Linkage

Native-mode compilers depend on a C toolchain; they may emit and compile assembly code, and use the linker.

Bytecode-mode compilers handle everything by themselves; they do not need a linker or other C tools (unless the source code uses interop to use libraries produced by another language system (C, Rust, etc.) ?)

Other tools in the distribution

The OCaml toolchain includes a variety of tools, most of which come in *.byte and *.opt variants. Some but not all come with a man page.

  • ocaml - a toplevel system (i.e. REPL) for OCaml

  • ocamlcmt - reads a .cmt file and prints related information

  • ocamldebug - the OCaml source-level replay debugger

  • ocamldep - dependency generator: scans source files and emits dependency information

  • ocamldoc - documentation generator

  • ocamllex - lexer generator

  • ocamlmklib - generate libraries with mixed C / Caml code

  • ocamlmktop - builds OCaml toplevels that contain user code preloaded at start-up

  • ocamlobjinfo - prints information from .cmo/.cmx/.cmi files

  • ocamlprof - OCaml profiler

  • ocamlrun - executes bytecode files produced by the linking phase of the ocamlc command.

  • ocamlrund - debug version of ocamlrun

  • ocamlruni - instrumented variant of ocamlrun (see Runtime tracing with the instrumented runtime)

  • ocamlyacc - parser generator

OPAM

Third-party Tools

ocamlfind and the findlib library

findlib is an OCaml package manager library. It has largely been supplanted by OPAM, but the metadata language it defines is used by OPAM.

ocamlfind is a commonly used command-line interface to the findlib library.

OPAM

OPAM is the standard OCaml package manager.

Dune

Dune is the most commonly used build system for OCaml. Many if not most OPAM packages use Dune.

OBazl is an alternative to Dune.

Other

  • codept - alternative dependency solver

  • cppo - preprocessor, modeled on the C preprocessor