REMOVED pragma (Was: Monad of no `return` Proposal (MRP): Moving `return` out of `Monad`)

On Sun, 27 Sep 2015, David Feuer wrote:

On Sep 27, 2015 9:56 PM, "Richard Eisenberg" wrote:

...

I like this idea -- I, for one, often forget to consider the effect legacy written material has. But if we're doing

this for Monad, why not just come up with a pragma so that the magic doesn't have to be baked in? As in, witness the new definition for Monad:

...

...

class Applicative m => Monad m where    ...    {-# REMOVED return "The `return` method has been removed from Monad. Use `pure` in Applicative instead" #-}

(Please fix my warning text.)

We people with direct access to GHC might not be the only ones who want to refactor a method out from a class.

That's an excellent idea, and I think it makes sense to offer it at the module level as well as the class level. Just change DEPRECATED to REMOVED when it's actually removed. Speaking of such, has the deprecated export proposal made any headway?

I like the idea of a REMOVED pragma very much. After a deprecated function is actually removed it is hard to find out how to fix the code. I often ignore DEPRECATED warnings because respecting them would break my code for older GHC versions.