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 |