deriving for GRose

GHC 6.6 used to be happy with the program below provided that i use "-fglasgow-exts -fallow-undecidable-instances"

data GRose ff a = GRose a (ff (GRose ff a))

The same program does NOT work with GHC 6.8, 6.8.1 and 6.8.2, even if I use the options "-fglasgow-exts -XUndecidableInstances". This is the error I get:

    No instance for (Show (ff (GRose ff a)))
      arising from the 'deriving' clause of a data type declaration
                   at domotest.hs:2:0-56
    Possible fix:
      add an instance declaration for (Show (ff (GRose ff a)))
    When deriving the instance for (Show (GRose ff a))

Trac metadata

Trac field	Value
Version	6.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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