Apologies, the subject of my previous email was wrong. It is about Data.Maybe.mapMaybe, not Data.Map.mapMaybe. On Wed, Nov 20, 2013 at 4:40 PM, Akio Takano wrote:

Hi,

Currently mapMaybe does not fuse at all. The attached patch implements necessary rules for fold/build fusion in both sides (the result and the second argument) to happen. When fusion does not happen, the function should behave exactly the same as before.

I ran some benchmarks, testing cases where fusion does and does not happen:

http://htmlpreview.github.io/?https://github.com/takano-akio/mapmaybe-benchm...

The benchmark code is:

https://github.com/takano-akio/mapmaybe-benchmarks/blob/master/main.hs

Discussion period: 2 weeks.

Thank you, Takano Akio