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

[Leo White <lpw25@cam.ac.uk>]

> I think this show a problem of how types propagate only in one direction.
>
> p1 and p2 are both the same type but p1 gets infered corectly while p2
> needs the type annotation to avoid a warning. Lets look at the types:
>
> [...]
>
> It would be nice if the type inference and disambiguation would allow
> type information to flow both ways. Not just from first use to last
> but also from last use to first. Up, down, left and right in the tree
> representation of the code.
>
> Maybe the use of p2.y with .* (or in general disambiguation on the
> expected type of the label) because it could lead to hard to follow
> resolution of ambiguous record use. But the p2.x is a clear indication
> of what type the programmer wanted.

While in a way it is the opposite of what you're asking for, you can get
more consistent behaviour by using the "-principal" argument:

    # let cross_product p1 p2 =
        p1.x *. p2.y -. p1.y *. p2.x
      ;;
    Characters 41-42:
          p1.x *. p2.y -. p1.y *. p2.x
                     ^
    Warning 41: this use of y is ambiguous.
    Characters 49-50:
          p1.x *. p2.y -. p1.y *. p2.x
                             ^
    Warning 41: this use of y is ambiguous.

Regards,

Leo