I am not sure how to report bugs against the current development version of GHC. Should this go into Trac? The current HEAD gives a spurious unused declaration when deriving Typable/Traversable Details Compiling against current HEAD (0ed9a2779a2adf0347088134fdb9f60ae9f2735b) Adding test('T9069w', extra_clean(['T9069.o', 'T9069.hi']), multimod_compile, ['T9069', '-Wall']) to testsuite/tests/deriving/should_compile/all.T results in +[1 of 1] Compiling T9069 ( T9069.hs, T9069.o ) + +T9069.hs:5:1: Warning: + The import of ‘Data.Foldable’ is redundant + except perhaps to import instances from ‘Data.Foldable’ + To import instances alone, use: import Data.Foldable() + +T9069.hs:6:1: Warning: + The import of ‘Data.Traversable’ is redundant + except perhaps to import instances from ‘Data.Traversable’ + To import instances alone, use: import Data.Traversable() *** unexpected failure for T9069w(optasm) The file being compiled is -------------------------------------------- {-# LANGUAGE DeriveTraversable #-} module T9069 where import Data.Foldable import Data.Traversable data Trivial a = Trivial a deriving (Functor,Foldable,Traversable) ---------------------------------------------