Non-H98 crusade, contd.
ross at soi.city.ac.uk
ross at soi.city.ac.uk
Sat Feb 26 20:39:50 EST 2005
On Sat, Feb 26, 2005 at 08:00:22PM -0500, ajb at spamcop.net wrote:
> Quoting ross at soi.city.ac.uk:
> > 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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