RE: [Haskell-cafe] Equality constraints in type families

| > Why not quite? | | Maybe I was thinking too much in terms of GHC's implementation, but | due to the lazy expansion type synonyms, the expansion is interleaved | with all the rest of type checking. But I think I now know what you | meant: the outcome should be *as if* type synonym expansion was done | as a pre-pass. Well, validity checking is done when (and only when) converting an HsType to a Type. (The former being a programmer written type.) That's just what we want. It's done by checkValidType, which is not at all interleaved. Once that check is done, the lazy expansion can, I think, be left to itself; no further checking is required. Simon