Deriviable type classes

[Sean Leather]

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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