[Caml-list] labels and optional arguments in 3.06

[Chris Hecker <checker@d6.com>]

The new optional label semantics seem to work pretty well for my
normal usage, however I've run across one thing I'd like to do that
doesn't seem to work (and a warning I don't understand):

> # let f ?(a = 1.0) ~b ~c = a *. b *. c;;
> Characters 12-15:
> Warning: This optional argument cannot be erased
>   let f ?(a = 1.0) ~b ~c = a *. b *. c;;
>               ^^^
> val f : ?a:float -> b:float -> c:float -> float = <fun>

First question:  what is this warning?

Second question:  I'd like to be able to call f with or without
specifying the optional argument, without labels:

> # f;;
> - : ?a:float -> b:float -> c:float -> float = <fun>
> # f 2.0 4.0;;
> - : float = 8.

works fine,

> # f ~a:2.0 2.0 4.0;;
> Characters 9-12:
>   f ~a:2.0 2.0 4.0;;
>            ^^^
> Expecting function has type b:float -> c:float -> float
> This argument cannot be applied without label

doesn't work.  I'd like to be able to use ~b and ~c for interface
documentation, but not be forced to use them, and have ?a be an
optional parameter.  This

> # f ~a:2.0 ~b:2.0 ~c:4.0;;
> - : float = 16.

works, of course, but it's really verbose.

Is there any way to make this work?

Chris



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