Non-H98 crusade, contd.

ross at ross at
Sat Feb 26 20:39:50 EST 2005

On Sat, Feb 26, 2005 at 08:00:22PM -0500, ajb at wrote:
> Quoting ross at
> > Indeed.  Of all the extensions implemented by both GHC and Hugs, the only
> > ones that seem ready are
> >
> > - rank 2 type signatures, and
> >
> > - polymorphic components for data constructors (giving them rank 2 types).
> Off the top of my head:
> - multi-parameter type classes

Reasonable in themselves, but limited in usefulness without some scheme to
deal with overlapping instances, which doesn't seem settled at this time.

> - pattern guards

GHC only

> - scoped type variables

Different treatment in GHC and Hugs.  Can you point at a formal calculus
corresponding to the version in GHC?

> - recursive "do"

The treatment of recursion isn't obviously ideal: conflicts with ordinary
do, and the semantics depends on the dependency analysis.

> - data declarations with no constructors

Minor, but harmless.

> - constraints on typeclass methods
> - instances on type synonyms

Yes, these two and the relaxation of polymorphic recursion should have
been in H98.

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