Restricted Data Types Now

[Jim Apple]

On 2/8/06, oleg at pobox.com <oleg at pobox.com> wrote:
> It seems we can emulate the restricted data types in existing
> Haskell.
...
> > {-# OPTIONS -fglasgow-exts #-}
> > {-# OPTIONS -fallow-undecidable-instances #-}

http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/13500

Indicates that we will no longer need undecidable instances for this.
Since we can check termination, and this simulates restricted data
types with no core language changes, why not do it?

Why not change the libraries in Haskell' to put formerly polymorphic
variables as class parameters?

Jim