Hi, On 2015-11-05 at 15:53:39 +0100, Greg Weber wrote:
Thanks for the clear revisions! It is unclear from the proposal how well the automatic re-factoring tool is expected to work.
Currently, Hs2010To201x does the following few things: When a `Monad` instance definition is detected in a module, - if needed, define respective `Functor` instance (AMP) - if needed, define respective `Applicative` instance (AMP) - if needed, refactor return/pure definitions into canonical form (MRP) This works fairly well for most common `Monad` instances. I ran it on Cabal's code-base (for which only the MRP refactoring was relevant), and the result looked very promising: https://gist.github.com/hvr/cd35fbcff9be6f3cb2a9 However, the major obstacle so far is CPP, which generally causes problems with other tooling as well, and in particular /can/ confuse ghc-exactprint. Another source of problems are orphan-instances (specifically when the `Applicative` instance is defined in a different module from the module where the `Monad` instance is defined) as the tool currently operates on single modules at a time. Finally, the less frequent cases of nested Monads which require to construct proper instance constraints for `Functor`/`Applicatives` instances are not handled adequately yet. Examples are `instance (Monad m) => Monad (ListT m)` or `instance (Monad m) => Monad (StateT s m)`. --HVR