Re: [Caml-list] Record field disambiguation in 4.01

[Jacques Garrigue <garrigue@math.nagoya-u.ac.jp>]

On 2013/03/10, at 8:39, Yaron Minsky <yminsky@gmail.com> wrote:

> This is all in the vein of complaining about a feature that has not
> yet been released, so, apologies if all of this is already known and
> plans are there for fixing it.
> 
> I've been playing around with a recent 4.01 snapshot of the compiler
> in OPAM, and have run against an interesting issue with the record
> field disambiguation.  In particular, I have some code that looks
> roughly like this:
> 
> open Core.Std
> 
> type posn = { x: float; y: float }
> 
> let cross_product p1 p2 =
>  p1.x *. p2.y -. p1.y *. p2.x
> ;;
> 
> And when I try to compile this, I get the following error:
> 
> File "geometry.ml", line 68, characters 13-14:
> Warning 41: this use of y is ambiguous.
> File "geometry.ml", line 1:
> Error: Error-enabled warnings (1 occurrences)
> Command exited with code 2.
> 
> This can be fixed by adding an annotation:
> 
> let cross_product p1 (p2:posn) =
>  p1.x *. p2.y -. p1.y *. p2.x
> ;;
> 
> A few concerns: one, it's really hard to figure out where the source
> of the conflict is from this message.  It would be nice to get some
> clue from the compiler as to the two definitions that are conflicting.

I see. This shouldn't be difficult.

> Also, I'm wondering if anyone has thoughts as to how much code this
> change will break?  The answer might be "quite a lot", and it might
> nonetheless be worth it.  But I'm curious what people's thoughts are.

Just to clarify: warning 41 is off by default.
You should just decide whether you want to enable it for core or not.
(The practice of using -w A -warn-error A is dangerous, as new warnings
may be added at any time)

	Jacques