deriving for GADTs
I'm pleased to see that GHC 6.12.1 will include deriving for GADTs. However, I discovered this in a quite accidental way. I tried appending deriving (Eq, Show)
to the end of my type declaration, without success, and decided to check whether there was a request in Trac for the feature, when I discovered ticket #3012 (closed). Sure enough, switching to a standalone deriving clause worked when I compiled my program in GHC 6.12.1 RC1.
It would be nice if this feature were more easily discoverable. I think it deserves mention in the release notes. Also, it would be great if the error message for the non-standalone deriving clause (Can't make a derived instance of ... / Constructor ... does not have a Haskell-98 type) suggested the standalone syntax.
Trac metadata
Trac field | Value |
---|---|
Version | 6.12.1 RC1 |
Type | FeatureRequest |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Documentation |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |