deriving Data.Typeable on phantom newtypes does not report that DeriveDataTypeable is needed
newtype Foo x = Foo deriving (Typeable)
reports the rather cryptic error message:
Can't make a derived instance of
Typeable (Foo x)' (even with cunning newtype deriving:) In the newtype declaration for
Foo'
When newtype is replaced with data, this much more useful error message is given:
Can't make a derived instance of
Typeable (Foo x)' (You need -XDeriveDataTypeable to derive an instance for this class) In the data type declaration for
Foo'
Trac metadata
Trac field | Value |
---|---|
Version | 6.9 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |