kindFunResult in monad transformer

This is probably related to the existing (fixed?) bug(s) about kindFunResult, but better safe than sorry.

I was writing a brainfuck interpreter, and tried changing this code:

getptrval = gets mem >>= \a -> gets ptr >>= lift . readArray a

to this (which probably wouldn't even work):

getptrval = liftM2 (lift . readArray) (gets ptr) (gets mem)

which gives this error message from GHC:

Brainfuck.hs:53:21:ghc: panic! (the 'impossible' happened)
  (GHC version 7.6.1 for x86_64-unknown-linux):
	kindFunResult
<<details unavailable>>

Related type information:

type BFMonad a = StateT BFState IO a
data BFState = BF {
    pc, ptr :: Int,
    mem     :: IOUArray Int Int,
    program :: UArray Int Char
}

Trac metadata

Trac field	Value
Version	7.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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