The type of evalContT should be generalized

[sjshuck]

[original issue 51 by @treeowl]

Now that Applicative has been a superclass of Monad for a while, I think it's time to update the type of evalContT. Currently, it's

evalContT :: Monad m => ContT r m r -> m r

but it works just fine with

evalContT :: Applicative m => ContT r m r -> m r

[sjshuck]

[original comment by ross a.k.a. @RossPaterson a.k.a. Ross Paterson]

That would mean bumping the base dependency to 4.8. I'm not sure.

[sjshuck]

[original comment by @ocramz]

Perhaps guarding the constraint with a bit of CPP (i.e. newer base versions would use Applicative) would help everyone?

[rajcspsg]

I'm taking this issue

[sjshuck]

Thanks!