Consistent indentation with ocamlformat?

Ecosystem
1

I’m looking to switch to ocamlformat, but the one thing I can’t figure out is how to get consistent indentation levels.

Example using default settings:

let () =
  (* 2 space indent *)
  []
  |> ListLabels.iter ~f:(fun () ->
         (* 7 space indent *)
         let () = () in
         ());
  []
  |> ListLabels.iter ~f:(function
       (* 5 space indent *)
       | () ->
           let () = () in
           ()
       | _ -> assert false);
  ListLabels.iter [] ~f:(fun () ->
      (* 4 space indent *)
      let () = () in
      ())

let a =
  (* 2 space indent *)
  match 0 with
  | 0 ->
      (* 4 space indent *)
      let () = () in
      ()
  | _ -> ()

Is there a collection of settings that will make ocamlformat to indent all of these by two spaces, so it looks like:

let () =
  (* 2 space indent *)
  []
  |> ListLabels.iter ~f:(fun () ->
    (* 2 space indent *)
    let () = () in
    ());
  []
  |> ListLabels.iter ~f:(function
    (* 2 space indent *)
    | () ->
      let () = () in
      ()
    | _ -> assert false);
  ListLabels.iter [] ~f:(fun () ->
    (* 2 space indent *)
    let () = () in
    ())

let a =
  (* 2 space indent *)
  match 0 with
  | 0 ->
    (* 2 space indent *)
    let () = () in
    ()
  | _ -> ()
1 Like
2

There is --max-indent that you could set to 2. It doesn’t always work and sometimes triggers weird behaviors. But probably better than nothing.

1 Like
3

Hmm that actually brings up a few cases that I want to be indented more than 2 spaces (like wrapped function arguments).

For the match part there’s cases-exp-indent=2. I think the thing that’s bothering me in the code above is that ocamlformat is indenting based on the start of the thing after |> instead of the start of the line. I wonder if there’s an option to turn that off?

For example, if the monad operator is longer it just keeps indenting:

  []
  >>>>>>>>>>> ListLabels.iter ~f:(fun () ->
                  (* 16 space indent *)
                  let () = () in
                  ())
4

I guess max-indent=4 and cases-exp-indent=2 gives me something tolerable, although the option I really want is “indent based on the previous line and not the end of the previous infix operator”

5

I believe that’s what max-indent is supposed to do. I invite you to open an issue on ocamlformat’s repo. The maintainers have been very responsive to all my requests to add configuration option or fix bugs.

6

Just for expectation setting purposes, while it is great to hear what people want, also realize that the implementation is fundamentally organized around the structure of parsed phrases, not “lines”. The default / normal case is for indentation to be based on where the enclosing phrase started. (For example, the comment in the code that reads 16 space indent is, to the implementation, a 4 space indent.) There are currently a number of exceptions, but each additional one is a special case, difficult to nigh impossible to implement, complicated, and a significant maintenance cost.

In a slightly different direction, how would you react if when the length of the infix operator exceeded some fixed length, a break was inserted after it instead of indenting the right-hand argument?

7

Just for expectation setting purposes, while it is great to hear what people want, also realize that the implementation is fundamentally organized around the structure of parsed phrases, not “lines”.

Yeah, I think that part of the design means ocamlformat will never work the way I want. I’ve decided to just run it on the janestreet profile and try not to think about it.

8

:frowning: It is a pretty basic point. For context, note that the original use case was a Reason to OCaml converter, which forced this design choice.

9

Yeah that makes sense :slight_smile: