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Simon Peyton Jones authored
Occurrences in terms are uses, in patterns they are not. In this way we get unused-constructor warnings from modules like this module M( f, g, T ) where data T = T1 | T2 Bool f x = T2 x g T1 = True g (T2 x) = x Here a T1 value cannot be constructed, so we can warn. The use in a pattern doesn't count. See Note [Patterns are not uses] in RnPat. Interestingly this change exposed three module in GHC itself that had unused constructors, which I duly removed: * ghc/Main.hs * compiler/ghci/ByteCodeAsm * compiler/nativeGen/PPC/RegInfo Their changes are in this patch.
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