2011/2/9 Simon Peyton-Jones: > Friends > > Just a heads-up. Pedro is working on implementing "Generic Defaults", as > described in his Haskell Symposium 2010 paper > www.dreixel.net/research/pdf/gdmh_nocolor.pdf > > It will replace (and improve on) the "Derivable type classes" stuff in GHC > at the moment, which was originally presented in a paper of that title that > Ralf and I wrote in the 2000 Haskell workshop > http://research.microsoft.com/en-us/um/people/simonpj/papers/derive.htm. > > The "Derivable type class" extension is barely used, I believe, and isn't > even documented in the manual. So I propose to switch from one to the > other, rather than to try to support both. This change will happen in GHC > 7.2 or 7.4, depending on when Pedro is done. > > Please yell if you are a secret user of derivable type classes, so this > change would discombobulate you. >
The only time I came across a use of it was in James Cheney's FreshLib [1]. I don't know if the latest version still uses it, though. There was also this bug [2] that prevented FreshLib from being compiled, but that is apparently fixed now. [1] http://homepages.inf.ed.ac.uk/jcheney/programs/freshlib/ [2] http://hackage.haskell.org/trac/ghc/ticket/2824 Regards, Sean
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