OCaml with OCamlBuild and Merlin

Project structure

This is an example project that uses OCamlBuild and Merlin.

- src/           <-- source code lives here
    awesome.ml   <-- An example module implementation
    awesome.mli  <-- An example module specification
    main.ml      <-- Main entry point
    test.ml      <-- Test harness (uses OCamlBuild)
  Makefile       <-- Driver for `make` (uses OCB)
  .merlin        <-- Merlin configuration
  _tags          <-- OCamlBuild configuration

Typing make will (hopefully!) generate a main binary, that you can run:

make
./main

The source code

The src/ directory defines three things:

• An example module Awesome (named awesome.ml) and its signature (awesome.mli). Note the .mli file is using the ocamldoc format.

• A main program that uses the Awesome module.

• A test module that uses the OUnit for unit tests.

The Makefile

Is just a wrapper around ocamlbuild, which is a standard use of Makefiles with ocamlbuild. OCamlBuild takes care of a lot of things for us (dependency resolution, for example), but we still want to be able to type make to build the project.

default: main

main: main.native

test: test.native

%.native: 
    ocamlbuild -use-ocamlfind $@
    mv $@ $*

.PHONY: test default

The project defines two phony targets so the developer can type make main or make test (and run main by default if they only type make). Then it shells out to ocamlbuild.

Running the test harness

newvpn16:example-ocaml-merlin micinski$ make test
ocamlbuild -use-ocamlfind test.native
Finished, 8 targets (4 cached) in 00:00:00.
mv test.native test
newvpn16:example-ocaml-merlin micinski$ ./test
.
Ran: 1 tests in: 0.00 seconds.
OK

Let's change something, change the definition of the test function in test.ml to:

let suite = "OUnit tests..." >:::  ["test_list_length" >::
    (fun () -> assert_equal "1" (str_of_t (succ one_t)))]

and now we get:

ocamlbuild -use-ocamlfind test.native
Finished, 8 targets (4 cached) in 00:00:00.
mv test.native test
newvpn16:example-ocaml-merlin micinski$ ./test
F
==============================================================================
Failure: OUnit tests...:0:test_list_length

not equal
------------------------------------------------------------------------------
Ran: 1 tests in: 0.00 seconds.
FAILED: Cases: 1 Tried: 1 Errors: 0 Failures: 1 Skip:  0 Todo: 0 Timeouts: 0.

Merlin .merlin file

The .merlin file in the main directory specifies project dependencies for Merlin:

PRJ awesome
S src

PKG ounit

B _build/src

• The first line names the project
• The second says that some source files live in the src directory
• The fourth says that we are using the ounit package (make sure you install it via OPAM!)
• The third says that built binaries live in _build/src (this is crucial, since Merlin seems to pick up signatures for it)

Example merlin use

Rename str_of_t to str_of_y and save the buffer, it will be highlighted with an error message:

Error: Unbound value str_of_y

You can also partially complete str_of_ and Merlin will auto fill a completion for you.