On 07-May-2000, S.D.Mechveliani <[EMAIL PROTECTED]> wrote:
> Marcin 'Qrczak' Kowalczyk <[EMAIL PROTECTED]> writes
>
> > Sample arguments are bad, because:
> > [5 points follow]
>
> But they are only for snobs.
That doesn't matter; we don't want to add a bad feature,
regardless of who is likely to use it.
> > 1. They present a confusing interface. This looks like a function,
> > but the real meaning is a constant. Neither mathematics nor
> > programming languages treat zero as a function from any unused
> > number to the zero value.
>
> zero `asTypeOf` x is also a function applied to x.
> Where is the difference?
See my earlier mail: `asTypeOf' is essentially a language construct.
> > 5. They hurt performance, Not always they can be optimized out.
>
> Why? zero `asTypeOf` x is as likely to be optimized as zero x.
That is not true. The reason is that `asTypeOf' is a (standard
Prelude) function, whereas `zero' is a class method. Since `asTypeOf'
has a trivial definition, any half-decent optimizing compiler will
inline it. Specializing class methods, on the other hand, is
more difficult.
> If for the former, the instance of `zero' is defined simply and can
> be, say in-lined, then the latter can too.
That is pretty much true. The problem comes when the compiler
*can't* figure out statically which instance of `zero' this
code will call.
> basAlgPropos introduces `zero x' because
> * Haskell has problems with constants in methods, in particular
> `asTypeOf` is often needed,
I don't buy that argument.
> * `zero x' fits the aim of implicit dynamic domains.
This one is much more interesting.
--
Fergus Henderson <[EMAIL PROTECTED]> | "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh> | of excellence is a lethal habit"
PGP: finger [EMAIL PROTECTED] | -- the last words of T. S. Garp.
