I'm on Ubuntu 16.10 and I've followed this, but now I have ghci 7.10.3, which still needs the the "let" in front of every function for use in places like Emacs org-mode's babel. Here's an example of what I have to do in org-mode to get it to run:

#+begin_src haskell

:set +m

let doubleSmallNumber4 x = if x > 0

then x

else x*2

doubleSmallNumber4 42

#+end_src

I've heard that an 8.+ version of ghci eliminates this issue. Is this true? If so, how can I upgrade my "stack."