Proposal: add fusion RULES for Data.Map.mapMaybe

[Akio Takano]

The proposal received support from two people, and got no objection, so I
created a ticket for it on the GHC trac.

https://ghc.haskell.org/trac/ghc/ticket/8595

Thank you,
Takano Akio

On Wed, Nov 20, 2013 at 4:40 PM, Akio Takano <tkn.akio at gmail.com> 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-benchmarks/blob/master/out.html
>
> The benchmark code is:
>
> https://github.com/takano-akio/mapmaybe-benchmarks/blob/master/main.hs
>
> Discussion period: 2 weeks.
>
> Thank you,
> Takano Akio
>
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