[Haskell-cafe] Impredicative Types

Gregory Crosswhite gcross at phys.washington.edu
Fri Nov 19 14:59:28 EST 2010

Awesome, thank you.  :-)  One more question out of pure curiosity, if 
you have the time:  What is allowing you to keep them in?  I thought 
that the problem was that they made a mess that touched every party of 
the type checker rather than being centralized in one place.  Was there 
a trick you discovered that now allows you to support them without 
creating such a mess?


On 11/19/10 11:45 AM, Simon Peyton-Jones wrote:
> Yes, impredicative types are still in, but in a simpler form than before, along the lines of QML
> http://research.microsoft.com/en-us/um/people/crusso/qml/
> I have been too busy with getting the new type checker working to describe or document it.  Notably, I have not yet added syntax for QML's rigid type annotations, which leads to a loss of expressive power.
> too much to do!
> Bottom line: if you are interested in impredicative polymorphism, let me know.  A good way to do so would be to register your interest on
> 	http://hackage.haskell.org/trac/ghc/ticket/4295
> Just add your email address to the cc list, *and* write a comment giving an example of how you are using impredicative poly, and pointing to any further info.  That'll help motivate me to do the remaining work!
> Thanks
> Simon
> |  -----Original Message-----
> |  From: haskell-cafe-bounces at haskell.org [mailto:haskell-cafe-bounces at haskell.org]
> |  On Behalf Of Gregory Crosswhite
> |  Sent: 19 November 2010 19:23
> |  To: Haskell Cafe
> |  Subject: [Haskell-cafe] Impredicative Types
> |
> |  Hey everyone!  I haven't had a chance to try out GHC 7 myself, but I saw
> |  in the documentation that Impredicative Types are still supported.  Is
> |  this true?  I thought that they were on their way out because they
> |  overcomplicated type checking;  has this plan been changed?
> |
> |  Cheers,
> |  Greg
> |  _______________________________________________
> |  Haskell-Cafe mailing list
> |  Haskell-Cafe at haskell.org
> |  http://www.haskell.org/mailman/listinfo/haskell-cafe

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