allow duplicate deriving / standalone deriving
I would like to avoid conditional compilation. Currently I need to write:
#if MIN_VERSION_Cabal(1,18,0)
-- cabal 1.18 has these instances
#else
deriving instance Typeable Flag
#endif
Would it be sane to have the deriving instance do nothing if the imported instance that clashes was also derived?
reifyInstances together with a fixed #8100 (closed) could allow faking this feature.
Trac metadata
Trac field | Value |
---|---|
Version | 7.6.3 |
Type | FeatureRequest |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
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Blocking | |
CC | |
Operating system | |
Architecture |