Thanks for fixing this, Simon! I can add tests if you haven't already... Cheers, Gabor On 3/7/14, git@git.haskell.org wrote:

Repository : ssh://git@git.haskell.org/ghc

On branch : master Link : http://ghc.haskell.org/trac/ghc/changeset/cdac487bcd9928d77738f6e79ead7b9bb4...

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commit cdac487bcd9928d77738f6e79ead7b9bb4bc00fd Author: Simon Peyton Jones Date: Fri Mar 7 16:45:55 2014 +0000

Make -XDeriveFunctor more generous about non-last arguments (Trac #8678)

When deriving Functor, Foldable, Traversable, we need only look at the way that the last type argument is treated. It's fine for there to be existentials etc, provided they don't affect the last type argument.

See Note [Check that the type variable is truly universal] in TcDeriv.

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cdac487bcd9928d77738f6e79ead7b9bb4bc00fd compiler/typecheck/TcDeriv.lhs | 88 +++++++++++++++----- compiler/typecheck/TcGenDeriv.lhs | 8 +- docs/users_guide/glasgow_exts.xml | 7 ++ testsuite/tests/deriving/should_compile/T8678.hs | 12 +++ testsuite/tests/deriving/should_compile/all.T | 1 + testsuite/tests/deriving/should_fail/T3101.stderr | 2 +- testsuite/tests/generics/GenCannotDoRep0_0.stderr | 3 +- testsuite/tests/generics/GenCannotDoRep1_0.stderr | 3 +- .../tests/typecheck/should_fail/tcfail086.stderr | 2 +- 9 files changed, 96 insertions(+), 30 deletions(-)

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