Use Data.Functor.Identity

[treeowl]

Data.Functor.Identity has just entered base, and includes some optimizations that may or
may not be relevant. For older versions, don't bother making Identity a
Monad instance--it's not exported, and that instance is never used.
Make applicativeTree slightly more readable. There doesn't seem to
be any reason to seq the quotient, as quotRem calculates that along
with the remainder.

[foxik]

Please rebase to current HEAD, because in the chunk

 #if MIN_VERSION_base(4,8,0)
 import Data.Coerce
+import Data.Functor.Identity (Identity(..))
 #endif

the MIN_VERSION_base(4,8,0) was replaced in #75 by __GLASGOW__HASKELL__. Nevertheless, the Data.Functor.Identity should be really used in MIN_VERSION_base(4,8,0) and its later usage on line 559 is conditioned agan by !MIN_VERSION_base(4,8,0).

[treeowl]

I think that should do the trick. Do you know why all the GHC HEAD builds fail always on Travis?

[foxik]

It seems the ChasingBottoms package has base < 4.8.

If you are interested, we could create a flag in the container.cabal allowing to compile tests without ChasingBottoms, which is used in only 2 out of 8 test-suites, until there is ChaginBottoms for newer GHC.