Dear GHCers, Maybe this question is more for Haskell-cafe, but since it involves language extensions as provided by GHC, it seems reasonable to post it here. The GHC user guide lists under 7.4 [1] the extensions to data types and type synonyms. My question involves 7.4.5 (although the overlap with 7.4.6 is considerable; maybe the two should be merged). A property of GADTs that I really appreciate is the fact that constructor contexts are made available by pattern matching (I don't quite understand why normal ADTs could do this, btw, but that's another question). The problem I have now, though, is that there doesn't seem to be a syntax to combine contexts and records in GADTs. Consider this program: data ContTest a where A :: Show a => a -> ContTest a data RecTest a where B { arg :: a } :: RecTest a data RecContTest a where C { showable :: Show a => a } :: RecContTest a a :: ContTest a -> String a (A a) = show a b :: Show a => RecTest a -> String b = show . arg c :: RecContTest a -> String c (C { showable = x }) = show x Both ContTest and RecTest work swimmingly (with functions a and b, respectively). However, GHC complains that it can not deduce Show for type a in function c. My definition of RecContTest is the only syntactical form I could come up with that GHC accepts. Is there a syntax for what I want here? Regards, Philip PS. As a side-note. In section 7.4.5, the manual states that: "At the moment, record updates are not yet possible with GADT-style declarations, so support is limited to record construction, selection and pattern matching." However, if I add: update org@(B {}) x = org { arg = x } and evaluate "b $ update (B True) False" the response is "False" as one would expect. Is this line in the user guide outdated, or is support for updates unstable or partial? [1]http://www.haskell.org/ghc/docs/latest/html/users_guide/data-type-extensions...