Important

We're archiving ocamllint as it's not used at Cryptosense anymore and we believe there are better and more flexible lint tools available than a standalone binary.

If you think otherwise and are interested in maintaining it, please don't hesitate to contact us at [email protected].

Ocamllint - detect common errors in OCaml code

What is ocamllint?

Ocamllint is a tool to find problematic constructions in OCaml code.

For example, consider the following piece of code:

let print_summary solutions =
  if List.length solutions = 0 then
    print_endline "No solutions"
  else
    print_endline "Some solutions were found"

This piece of code is correct, but it is doing too much work: if the solutions list is long, it will take a long time to compute its length, only to check whether this length is zero.

When compiled with ocamllint, a warning message will be displayed:

File "example.ml", line 2, characters 5-30:
(ocamllint) Use = []

Indeed, a more efficient way to do it is

let print_summary solutions =
  if solutions = [] then
    print_endline "No solutions"
  else
    print_endline "Some solutions were found"

Or using pattern matching:

let print_summary solutions =
  match solutions with
  | [] -> print_endline "No solutions"
  | _::_ -> print_endline "Some solutions were found"

Neither of these versions will trigger the above warning.

What is ocamllint NOT?

Due to the way it is implemented, ocamllint does not deal with concrete syntax. This means that it can not detect individual tokens, only abstract syntax.

How to use ocamllint

First you need to install ocamllint as an ocamlfind package. make followed by make install will do the right thing. An OPAM package is also in the works.

Then you only need to pass -package ocamllint.ppx to your build system. If you are using ocamlbuild, adding true: package(ocamllint.ppx) to your _tags file should work.

How to configure ocamllint

Similarly to how ocamlbuild works, it is necessary to write a plugin to modify the configuration. It is a dynamically-linked file from which one has to call Ocamllint.Plugin.set_config. The example_plugin.ml file is, well, an example. This plugin disables a warning. It can be built using make example.

When the ppx rewriter is loaded without an argument, it will use a default configuration:

% ocamlfind ppx_tools/rewriter -ppx "ocamlfind ocamllint/ppx_lint.native" -str
'let y = []@[] in let x = 3 in x'
File "", line 1, characters 17-31:
(ocamllint) Useless let binding
File "", line 1, characters 8-13:
(ocamllint) List operation on litteral: @
let _ = let y = [] @ [] in let x = 3 in x

If you pass an option to the rewriter, it will load the configuration:

% ocamlfind ppx_tools/rewriter -ppx "ocamlfind ocamllint/ppx_lint.native
_build/example_plugin.cmxs" -str 'let y = []@[] in let x = 3 in x'
File "", line 1, characters 8-13:
(ocamllint) List operation on litteral: @
let _ = let y = [] @ [] in let x = 3 in x

Contributing

New rules are welcome! Write a test in tests.ml, a rule in rules.ml and you should be set.