ghc.exe: panic! (the 'impossible' happened)

When compiling an example from Real World Haskell, I get the following error message:

    Prelude> :l Prettify.hs
    [2 of 2] Compiling Prettify         ( Prettify.hs, interpreted )
    ghc.exe: panic! (the 'impossible' happened)
      (GHC version 7.4.2 for i386-unknown-mingw32):
            nameModule show{tv apB}

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

    >

The example contains simple function stubs which are used by another module:

    module Prettify
        ( string
        , text
        , double
        ) where

    import SimpleJSON

    data Doc = ToBeDefined
        deriving (show)

    string :: String -> Doc
    string str = undefined

    text :: String -> Doc
    text str = undefined

    double :: Double -> Doc
    double num = undefined

Trac metadata

Trac field	Value
Version	7.4.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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