type families GHC "impossible happened"
the code: http://hpaste.org/2860?\#a0
produces the following error:
$ ghci Foldable.hs
GHCi, version 6.8.0.20070921: http://www.haskell.org/ghc/ :? for help
Loading package base ... linking ... done.
[1 of 1] Compiling Data.Collections.Foldable ( Foldable.hs, interpreted )
ghc-6.8.0.20070921: panic! (the 'impossible' happened)
(GHC version 6.8.0.20070921 for i386-unknown-linux):
check_tau_type
main:Data.Collections.Foldable.FoldElem{tc rE4} t{tv aFj} [tv]
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug