repeatable instance of "impossible" error

[Donald Bruce Stewart]

simonmar:
> > 
> >     Please report it as a compiler bug to
> >     glasgow-haskell-bugs at haskell.org, or
> > http://sourceforge.net/projects/ghc/. 
> 
> plugins depends on Cabal, doesn't it?  I suspect that Cabal-1.0 is your
> missing package.

Ah ha! Of course, silly me.
Rebuilding plugins with the new cabal fixes the panic when building yi.

-- Don