"tuareg-eval-phrase" Error with class type

[Fourchaux]

OCaml 4.11.1 - Tuareg 2.2.0 - The Merlin toolkit v3.3.9, for OCaml 4.11.1 - Emacs 28.0.50

Example from https://caml.inria.fr/pub/docs/manual-ocaml-4.11/objectexamples.html#s:class-interfaces

class type restricted_point_type =
  object
    method get_x : int
    method bump : unit
  end;;

• Error with "tuareg-eval-phrase" :

Line 1, characters 5-7:
1 | class;;
         ^^
Error: Syntax error

• OK with "tuareg-eval-region" :

class type restricted_point_type =
  object method bump : unit method get_x : int end

[mattiase]

This patch seems to work. Drawback: the indentation of your example is not preserved; that is,

class type restricted_point_type =
  object
    method get_x : int
    method bump : unit
  end

is indented as

class type restricted_point_type =
object
  method get_x : int
  method bump : unit
end

which corresponds to the indentation of class definitions:

class c =
object
  method m = 1
end

On the other hand, putting object at the end of the first line (analogously to module type M = sig...) now produces decent indentation:

class type restricted_point_type = object
  method get_x : int
  method bump : unit
end;;

which was not the case before.

In other words: the patch fixes the class type parsing. Is the indentation acceptable? If not, what is the desired style? (I don't use classes much but would probably prefer the object-on-the-first-line style myself.)

[Fourchaux]

No more 'Syntax error' : well done.

Note: I don't have your indentation problem.
(for info I'm using ocp-indent)

So, for me, this issue can be closed.
Thank you very much.

[mattiase]

Thanks for confirming, and yes, ocp-indent uses different rules. It appears that tuareg's class indentation,

class c =
object
  method m = ()
end

is very much intended (see bcad60e) but it's unclear to what extension it describes a consensus among OCaml programmers. The OCaml source tree itself is inconsistent in this respect, but that is not unexpected for a long-lived code base with many contributors.

It looks like the indentation consequences of the patch are neutral at worst, and fixing the parsing bug is worth it.

[monnier]

Thanks for confirming, and yes, ocp-indent uses different rules. It appears that tuareg's class indentation, ``` class c = object method m = () end ``` is very much intended (see bcad60e) but

It should be easy to add a config var to control that, if we want to. We could also make it so that we get: ``` class c = object method m = () end ``` but still keep ``` class c = object method m = () end ``` which has the advantage of allowing the programmer to choose between the two indentations without having to tweak a config var (so it works the same for all those using Tuareg).

it's unclear to what extent it describes a consensus among OCaml programmers. The OCaml source tree itself is inconsistent in this respect, but that is not unexpected for a long-lived code base with many contributors.

The lack of a good auto-indenter for much of the life of (O)Caml made for a rather anarchic style, I guess (I haven't looked enough at other people's OCaml code to be sure, but that's what I'd expect from my experience with SML).

It looks like the indentation consequences of the patch are neutral at worst, and fixing the parsing bug is worth it.

And it shouldn't be terribly hard to change the indentation separately if needed.

[mattiase]

We could also make it so that we get:

class c =
  object
    method m = ()
  end

but still keep

class c = object
  method m = ()
end

Yes, that would coincide with ocp-indent – I think that would be preferable, and class type should be laid out the same way. However, I'm not sure what the best way to accomplish that would be; SMIE indentation code is still somewhat of a mystery to me.

It looks like the indentation consequences of the patch are neutral at
worst, and fixing the parsing bug is worth it.

And it shouldn't be terribly hard to change the indentation separately
if needed.

This patch OK then?

[mattiase]

This should now be fixed; close if you agree.

[Fourchaux]

Done.