Oh, now I get it, thanks. This message concerns design choices for record-syntax-related GHC extensions. Lennart, pls tune in. You don’t need to have read the thread to understand this message. | I think that Even refers to an example like this: | | module A where | data A = A { a :: Int } | | The following works: | | {-# LANGUAGE NamedFieldPuns #-} | module B where | import A | f (A { a }) = a | | However, if we import "A" qualified, then punning does not seem to work: | | {-# LANGUAGE NamedFieldPuns #-} | module B where | import qualified A | f (A.A { a }) = a | | This results in: Not in scope: `a' Right. What is happening is that GHC looks up the first 'a' (the one on the LHS) and finds it not in scope. If you add -XDisambiguateRecordFields, it works fine. But admittedly, the error message is unhelpful. I could improve that. Now on to the suggested change: | {-# LANGUAGE NamedFieldPuns #-} | module B where | import qualified A | | f (A.A { A.a }) = a | | This results in: Qualified variable in pattern: A.a | | Even is suggesting that instead of reporting an error, in the second | case we could use the translation: | | f (A.A { A.a }) = a --> f (A.A { A.a = a }) | | (i.e., when punning occurs with a qualified name, use just the | unqualified part of the name in the pattern) Yes, that'd be possible. But it seems debatable -- it doesn't *look* as if the pattern (A.A { A.a }) binds 'a' -- and it seems even less desirable in record construction and update. To be concrete, would you expect these to work too? g a = A.A { A.a } --> g a = A.A { A.a = a } h x a = x { A.a } --> h x a = a { A.a = a } In these cases, I think the abbreviated code looks too confusing. With -XDisambiguateRecordFields you could say g a = A.A { a } which seems better. (But there's no help for record update, since we don’t know which data constructor is involved.) So my current conclusion is: improve the error message, perhaps suggesting the flag -XDismabiguateRecordFields, but don't add the change you suggest. Comments? Simon