Looking for help writing some GHC RULES

David Feuer david.feuer at gmail.com
Tue Jul 22 23:34:36 UTC 2014

These rules seem ... weird. Why, for example, do we need a special
mapFB/mapFB rule? Shouldn't map f . map g translate to a
build/foldr/build/foldr, fuse to build/foldr, and then translate back to
map? Is this a case of something that almost works but not quite, and that
needs patching up for a lot of cases?
On Jul 22, 2014 6:53 PM, "wren romano" <winterkoninkje at gmail.com> wrote:

> On Tue, Jul 22, 2014 at 6:42 PM, David Feuer <david.feuer at gmail.com>
> wrote:
> > I'm looking for some help writing some translate/untranslate rules to
> > implement fusion for a couple of basic functions (the ones I'm looking at
> > right now are takeWhile and scanr, but there may be others). I have a
> > translation for takeWhile that seems to be at least decent, and one for
> > scanr that is completely untested. I've never mucked about with GHC
> > however, so I don't even know where to begin.
> Probably the best place to start is to take a look at the source for
> GHC.Base and GHC.List, in particular the rules for map and filter
> capture the overarching pattern of how to stage the different rules.
> <
> http://hackage.haskell.org/package/base-
> >
> <
> http://hackage.haskell.org/package/base-
> >
> --
> Live well,
> ~wren
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