Hi, I'm getting the panic below when building darcs 2.8 with GHC 7.6. It'll take some effort to cut it down or give repro instructions for an uncut-down version (I needed to hack a lot of underlying packages to be able to even get as far as doing this build), so could someone confirm that it's worth it before I do so? I can't spot anything already reporting this in trac. Cheers, Ganesh ghc.exe: panic! (the 'impossible' happened) (GHC version 7.6.0.20120810 for i386-unknown-mingw32): coVarsOfTcCo:Bind cobox{v a6Czs} [lid] = cobox{v a6CTr} [lid] `cast` (<main:Darcs.Test.Patch.WithState.WithState{tc r1LL8} model{tv tC} [tv] (main:Darcs.Witnesses.Ordered.FL{tc r1Dy1} prim{tv ty} [tv] main:Darcs.Witnesses.Ordered.:>{tc r1Dyc} main:Darcs.Witnesses.Ordered.FL{tc r1Dy1} prim{tv ty} [tv])> ghc-prim:GHC.Types.~{(w) tc 31Q} main:Darcs.Test.Patch.WithState.WithState{tc r1LL8} (Sym cobox{v a6CSH} [lid]) <main:Darcs.Witnesses.Ordered.FL{tc r1Dy1} prim{tv ty} [tv] main:Darcs.Witnesses.Ordered.:>{tc r1Dyc} main:Darcs.Witnesses.Order ed.FL{tc r1Dy1} prim{tv ty} [tv]>) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug