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Polymorphic Variants
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Date: 2007-01-17 (23:07)
From: Tom <tom.primozic@g...>
Subject: Re: [Caml-list] Polymorphic Variants
> Yes: I prefer things the way they are.

I don't mean an revolution. Rather a symbiosys.

You can add overloading to ML but you must then add lots of type annotations
> to your code. For example, vector length:
>   let length (x, y) = sqrt(x*.x +. y*.y)
> becomes:
>   let length (x : float, y : float) = sqrt(x*x + y*y)
> So you've saved the "." three times at the cost of ": float" twice because
> the
> overloaded * and + don't provide enough type information. You can
> complicate
> the type inferer to counteract this but then other type errors will become
> increasingly obscure and the programmer will be forced to learn the quirks
> that you've added in order to debug their code.

3 solutions:
  * sqrt has type of float -> float and the compiler infers float arguments
  * you write +. and *. (at least once) (those operators could be still
available, don't you think so?)
  * let the compiler overload your function ( length : (int * int) -> float;
length : (float * float) -> float) and then drop the "int" one as you never
ever used it in your code.

> Finally, I don't want my types discovered at run-time because it makes my
> code
> slower and uses more memory. I'd rather have to box manually, so fast code
> is
> concise code.

More memory is used by polymorphic variants too. And the records could be
optimised so that type information is only added when it is needed by the

>From my point of view, your suggestions are mostly steps backwards (towards
> Lisp, C++ etc.).

Thank you for your comment :)

- Tom