7.6.1 RC1 panic "coVarsOfTcCo:Bind"

[Simon Peyton-Jones]

Ah.  Hmm.  I see.

Can you try this in TcEvidence

    -- We expect only coercion bindings
    go_bind :: EvBind -> VarSet
    go_bind (EvBind _ (EvCoercion co)) = go co
    go_bind (EvBind _ (EvId v))        = unitVarSet v
    go_bind other = pprPanic "coVarsOfTcCo:Bind" (ppr other)

with this instead?

    -- We expect only coercion bindings, so use evTermCoercion 
    go_bind :: EvBind -> VarSet
    go_bind (EvBind _ tm) = go (evTermCoercion tm)

I think that'll fix it.

Simon

| -----Original Message-----
| From: glasgow-haskell-users-bounces at haskell.org [mailto:glasgow-
| haskell-users-bounces at haskell.org] On Behalf Of Ganesh Sittampalam
| Sent: 22 August 2012 06:32
| To: glasgow-haskell-users at haskell.org
| Subject: 7.6.1 RC1 panic "coVarsOfTcCo:Bind"
| 
| 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
| 
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