[Haskell-cafe] Missing Functor instances in GHC 7?

Sebastian Fischer fischer at nii.ac.jp
Fri Dec 10 07:39:55 CET 2010

On Fri, 2010-12-10 at 14:35 +0900, Sebastian Fischer wrote:
> Yes, I cannot find the Functor instance for ((->) r).

As the Applicative instance for ((->) r) depends on the Functor instance
I "only" needed to go through the imports of Control.Applicative to find
that the Functor instance of ((->) r) is defined in
Control.Monad.Instances. If I import this module into GHCi, it finds the

Interestingly, if I import only Control.Applicative from within GHCi, it
does not find the instances defined in Control.Monad.Instances although
this module is imported in Control.Applicative. On the other hand, if I
write a file containing the line 'import Control.Applicative' and load
this file in GHCi then the instances from Control.Monad.Instances are

Apparently, importing a module in GHCi differs from importing it in a
Haskell file and loading this into GHCi.


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