Hello, I am affected by this error src/Hkl/Xrd/OneD.hs:238:49-52: Could not deduce (Key a ~ Key b0) from the context (Frame a) bound by the type signature for getPoniExtRef :: Frame a => XRDRef (Key a) -> IO PoniExt at src/Hkl/Xrd/OneD.hs:235:18-56 NB: `Key' is a type function, and may not be injective The type variable `b0' is ambiguous Possible fix: add a type signature that fixes these type variable(s) Expected type: Nxs (Key b0) Actual type: Nxs (Key a) In the second argument of `withDataFrameH5', namely nxs' In the first argument of `(>->)', namely `withDataFrameH5 h5file nxs' (gen output f) yield' In the first argument of `toListM', namely `(withDataFrameH5 h5file nxs' (gen output f) yield >-> hoist lift (frames' [idx]))' I looked at this http://stackoverflow.com/questions/20870432/type-family-vs-data-family-in-br... So in your opinion it would be better to use a data family instead of a type familly ? Cheers