Uncaught kind error leads to the 'impossible' happening
data F c a = F (c a)
data Val c a = Val (F c) a --- should produce a kind error but doesn't
t = Val (F [True]) False --- here we get the impossible
Here is a run
dhcp38-137:~/writing/exrep sweirich$ ghci test.hs
___ ___ _
/ _ \ /\ /\/ __(_)
/ /_\// /_/ / / | | GHC Interactive, version 6.4, for Haskell 98.
/ /_\\/ __ / /___| | http://www.haskell.org/ghc/
\____/\/ /_/\____/|_| Type :? for help.
Loading package base-1.0 ... linking ... done.
Compiling Main ( test.hs, interpreted )
ghc-6.4: panic! (the `impossible' happened, GHC version 6.4):
Unify.unifyTauTyLists: mismatched type lists!
Please report it as a compiler bug to glasgow-haskell-bugs@haskell.org,
or http://sourceforge.net/projects/ghc/.