Warn about derivable instances
GHC can derive a lot of instances by itself, and can sometimes (with GeneralizedNewtypeDeriving) do so better than anyone else. I'd like to be able to get a warning about any instance that's "obviously equivalent" to the one that would be derived, for some suitable values of "obviously" and "equivalent".
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.9 |
| Type | FeatureRequest |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
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| Operating system | |
| Architecture |