"panic! (the 'impossible' happened)" compiling code using arrows and elimReader (test case included)

In trying to debug a different issue, I ran ghci on one of the modules in Serialist, and encountered a ghc panic. I managed to reduce it down to the following minimal test case:

{-# LANGUAGE Arrows #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE RecordWildCards #-}

import Control.Arrow
import Control.Arrow.Transformer.Reader

newtype ByteString = FakeByteString String

pathInfo :: Monad m => m String
pathInfo = undefined

requestMethod :: Monad m => m String
requestMethod = undefined

getInputsFPS :: Monad m => m [(String, ByteString)]
getInputsFPS = undefined

class HTTPRequest r s | r -> s where
    httpGetPath :: r -> String
    httpSetPath :: r -> String -> r
    httpGetMethod :: r -> String
    httpGetInputs :: r -> [(String, s)]

data CGIDispatch = CGIDispatch {
    dispatchPath :: String,
    dispatchMethod :: String,
    dispatchInputs :: [(String, ByteString)]
}

instance HTTPRequest CGIDispatch ByteString where
    httpGetPath = dispatchPath
    httpSetPath r s = r { dispatchPath = s }
    httpGetMethod = dispatchMethod
    httpGetInputs = dispatchInputs

runDispatch :: (Arrow a, ArrowAddReader CGIDispatch a a', Monad m) => a b c -> m (a' b c)
runDispatch a = do
    dispatchPath <- pathInfo
    dispatchMethod <- requestMethod
    dispatchInputs <- getInputsFPS
    return $ proc b -> (| elimReader (a -< b) |) CGIDispatch { .. }

Running "ghci TestCase.hs" produces this panic:

GHCi, version 7.0.2: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Main             ( TestCase.hs, interpreted )
ghc: panic! (the 'impossible' happened)
  (GHC version 7.0.2 for x86_64-unknown-linux):
	addTickHsExpr
    (|/\(@ a{tv av7} [sk]).
      ((arrows-0.4.4.0:Control.Arrow.Internals.elimReader{v rg4} [gid[ClassOp]])
       @ main:Main.CGIDispatch{tc rot}
       @ a{tv auK} [sk]
       @ a'{tv auL} [sk]
         $dArrowAddReader{v ava} [lid])
      @ a{tv av7} [sk]
      @ c{tv auO} [sk]
        ((a{v ap8} [lid] -< b{v apc} [lid]))|)

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

> 

Trac metadata

Trac field	Value
Version	7.0.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	jamey@minilop.net
Operating system
Architecture