Incorrect "Defined but not used" warning when using GeneralizedNewtypeDeriving
When compiling
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# OPTIONS_GHC -Wall -Werror #-}
module Bug(P, runP) where
import Control.Monad.Identity(Identity, runIdentity)
newtype P a = P { unP :: Identity a } deriving Monad
runP :: P a -> a
runP = runIdentity . unP
I get
Bug.hs:7:14: Warning: Defined but not used: data constructor `P'
although the constructor is used in the derived Monad instance. This is obviously not a show stopper, but it forces me to rewrite what to me looks like an OK program if I want to stick to the given OPTIONS_GHC.
Trac metadata
Trac field | Value |
---|---|
Version | 6.8.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | Unknown |
Architecture | Unknown |