[Haskell-cafe] confusion about 'instance'....

[Henning Thielemann]

On Thu, 10 Jan 2008, Nicholls, Mark wrote:

> > Existential:
> > newtype Numeric  = forall a. Num a => Numeric a
> >
>
> My compiler doesn't like this...." A newtype constructor cannot have an
> existential context,"
>
> > Universal:
> > newtype Numeric' = Numeric' (forall a. Num a => a)
>
> Not so sure I understand the difference here.....

Looks like
  http://www.haskell.org/haskellwiki/Generic_number_type