[haskell-llvm] (StructFields s) vs. IsType (Struct s)

[Henning Thielemann]

Maybe this is a logical problem:

GHC says

     Could not deduce (llvm-0.10.0.0:LLVM.Core.Type.StructFields s)
       from the context (IsType (Struct s), ...)
     ...
     Possible fix:
       add (llvm-0.10.0.0:LLVM.Core.Type.StructFields s) to the context ...


I could just add the (StructFields s) constraint, but StructFields is not 
exported. I thought that adding (IsType (Struct s)) is also ok, since the 
llvm package exports the instance:
    StructFields s => IsType (Struct s)

Has anyone an idea, why GHC does not accept my (IsType (Struct s)) 
constraint?