Well, there are the *compat packages:

Base-compat
Transformers-compat
Mtl-compat 

Etc. They do centralize the ifdefs and give you compatibility with ‎GHC 7.*. I recently adopted the last two ones and they work like a charm. I am yet to adopt base-compat, so I don't know what the experience is with it. 

Michał

From: Sven Panne
Sent: Monday, October 5, 2015 9:27 AM
To: Simon Thompson
Cc: Michał J Gajda; haskell-prime@haskell.org List; Haskell Libraries; haskell cafe; Graham Hutton
Subject: Re: [Haskell-cafe] Monad of no `return` Proposal (MRP): Moving `return` out of `Monad`

2015-10-05 11:59 GMT+02:00 Simon Thompson <s.j.thompson@kent.ac.uk>:
[...] It’s really interesting to have this discussion, which pulls in all sorts of well-made points about orthogonality, teaching, the evolution of the language and so on, but it simply goes to show that the process of evolving Haskell is profoundly broken. [...]

I wouldn't necessarily call the process "broken", but it's a bit annoying: Because of the constant flux of minor changes in the language and the libraries, I've reached the stage where I'm totally unable to tell if my code will work for the whole GHC 7.x series. The only way I see is doing heavy testing on Travis CI and littering the code with #ifdefs after compilation failures. (BTW: Fun exercise: Try using (<>) and/or (<$>) in conjunction with -Wall. Bonus points for keeping the #ifdefs centralized. No clue how to do that...) This is less than satisfactory IMHO, and I would really prefer some other mode for introducing such changes: Perhaps these should be bundled and released e.g. every 2 years as Haskell2016, Haskell2018, etc. This way some stuff which belongs together (AMP, FTP, kicking out return, etc.) comes in slightly larger, but more sensible chunks.

Don't get me wrong: Most of the proposed changes in itself are OK and should be done, it's only the way they are introduced should be improved...