[Haskell-cafe] Impredicative Types

Simon Peyton-Jones simonpj at microsoft.com
Fri Nov 19 14:45:30 EST 2010

Yes, impredicative types are still in, but in a simpler form than before, along the lines of 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
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!



|  -----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
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