Your first point is also true for procedural programming languages, but at least in Haskell you know that if something is, say, a functor then you know what sort of things you can do with that value. I think it should be possible for an IDE to suggest functions if you used the reverse application operator:

  [1, 2, 3] & 
              ^-- suggestion here

Unfortunately this wouldn't be very idiomatic in Haskell, maybe in Idris with |> this would make more sense?