Uniqueness of principle type? (was Re: [Haskell-cafe] Type vs TypeClass duality)

[TJ]

On 10/23/07, Jules Bean <jules at jellybean.co.uk> wrote:
> I believe it is to do with the requirement that expressions have a
> unique principle type. Certainly in principle the algorithm you outline
> is possible, but I don't know what else you would lose.

I'm not familiar with the term "principal type". I shall have to study it.

> > And I would like to say that whether or not I need it is not the
> > issue, as I currently do not in fact need it. This is a study of the
> > Haskell language not my possible practical applications of it.
>
> Whether one needs it, or does not need it, is indeed an issue: any
> change to the type inference algorithm has a cost. That cost has to be
> judged against the value of it. If an extension is seldom needed, then
> its value is low, so the cost is unlikely to be considered worth it. If
> an extension is frequently need and the cost is low, then that argues
> for it..

Ah... harsh realities of engineering. Well I hope this is judged to be
important enough to be included in a future revision of Haskell.


Thanks,

TJ