[GHC] #13258: GHC head 8.1.20170209 does not compile package 'mono-traversable'

[GHC]

#13258: GHC head 8.1.20170209 does not compile package 'mono-traversable'
-------------------------------------+-------------------------------------
           Reporter:  clinton        |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Not sure if this is a bug in 'mono-traversable' or GHC but I thought it
 was worth reporting in any case. GHC head 8.1.20170209 is the version
 used:

 {{{
     Configuring mono-traversable-1.0.1.1...
     Preprocessing library mono-traversable-1.0.1.1...
     [1 of 5] Compiling Data.MonoTraversable ( src/Data/MonoTraversable.hs,
 .stack-work/dist/x86_64-linux/Cabal-1.25.0.0/build/Data/MonoTraversable.o
 )

     /tmp/stack12856/mono-
 traversable-1.0.1.1/src/Data/MonoTraversable.hs:144:13: error:
         • The default type signature for omap:
             forall (f :: * -> *) a.
             (Functor f, Element (f a) ~ a, f a ~ mono) =>
             (a -> a) -> f a -> f a
           does not match its corresponding non-default type signature
         • When checking the class method:
             omap :: forall mono.
                     MonoFunctor mono =>
                     (Element mono -> Element mono) -> mono -> mono
           In the class declaration for ‘MonoFunctor’
         |
     144 |     default omap :: (Functor f, Element (f a) ~ a, f a ~ mono)
 => (a -> a) -> f a -> f a
         |             ^^^^
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13258>
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