[Haskell-cafe] Impredicative Types

[Simon Peyton-Jones]

read the QML paper! that's the trick.  simpler, but with a heavier annotation burden than the more sophisticated approaches

|  -----Original Message-----
|  From: Gregory Crosswhite [mailto:gcross at phys.washington.edu]
|  Sent: 19 November 2010 19:59
|  To: Simon Peyton-Jones
|  Cc: Haskell Cafe; glasgow-haskell-users at haskell.org
|  Subject: Re: [Haskell-cafe] Impredicative Types
|  
|  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?
|  
|  Cheers,
|  Greg
|  
|  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
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