I hit "send" too early, so here's the incomplete section completed: On 2015-10-06 at 18:47:08 +0200, Herbert Valerio Riedel wrote: [...]
In the specific case of MRP, I can offer you a Wall-perfect transition scheme by either using `ghc-options: -fno-mrp-warnings` in your cabal-file, or if that doesn't satisfy you, we can delay phase1 (i.e. redundant return-def warnings) to GHC 8.2:
Now you can continue to write `return = pure` w/o GHC warning bothering you until GHC 8.2, at which point the 3-year-window will reach to GHC 7.10.
Then starting with GHC 8.2 you can drop the `return` definition, and
...keep supporting a 3-year-window back till GHC 7.10 (which incorporates AMP and doesn't need `return` explicitly defined anymore) without CPP. And since you don't define `return` anymore, you don't get hit by the MRP warning either, which would start with GHC 8.2. GHC can keep providing as long as we want it to, and consider `return` being an extra method of `Monad` simply a GHC-ism. Future Haskell books and learning materials will hopefully be based on the next Haskell Report incorporating the AMP and stop referring to the historical `return` accident (which I consider badly named anyway from a pedagogically perspective). Code written unaware of `return` being a method of Monad will work anyway just fine. Do you see any problems with this scheme?