Niklas Broberg:
I haven't payed much attention to how much of type families is/should
be implemented for 6.8.2. What of equality constraints? The following
parses alright, but can't be used it seems.
------------------------------------
module Foo where
class C a where
proof :: a
instance (a ~ Int) => C a where
proof = 1
------------------------------------
%> ghci -fglasgow-exts -XUndecidableInstances Foo.hs
GHCi, version 6.8.2: http://www.haskell.org/ghc/ :? for help
Loading package base ... linking ... done.
[1 of 1] Compiling Foo ( Foo.hs, interpreted )
Ok, modules loaded: Foo.
*Foo> proof :: Int
: panic! (the 'impossible' happened)
(GHC version 6.8.2 for i386-unknown-mingw32):
nameModule $dC{v aoz}
Please report this as a GHC bug: http://www.haskell.org/ghc/
reportabug
------------------------------------
I would follow that last advice if I knew this was *supposed* to
work. :-)
It is supposed to work in 6.9. I am sorry, but type families are not
an officially supported feature in 6.8.x, and hence, any bug fixes
that requires invasive changes in the type checker will not be merged
into the 6.8 branch (and by now the 6.8 and 6.9 code bases diverged
quite a bit). This is simply to ensure the stability of the stable
branch. Type families will be properly supported in 6.10.
Manuel
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