Proposal: Make GHC.Arr.listArray slightly stricter to allow fusion

[David Feuer]

Oh, I think I am a fool! That'll show me to post to the list at such an
absurd hour.

On Thu, Nov 13, 2014 at 6:33 AM, Joachim Breitner <mail at joachim-breitner.de>
wrote:

> Hi,
>
>
> Am Donnerstag, den 13.11.2014, 05:22 -0500 schrieb David Feuer:
> > Currently, GHC.Arr.listArray is pretty lazy:
> >
> > listArray (1,3) $ [1,2,3] ++ undefined
> >
> > will work perfectly fine.
> >
> > This is actually lazier than the current array:
> >
> > array (1,3) $ [(1,1), (2,2), (3,3)] ++ undefined = undefined
> >
> > Unfortunately, I don't think it's possible to make listArray fuse with
> > a list producer while preserving quite that level of laziness. If
> > we're willing to be slightly stricter, however, I think everything
> > works. Specifically, I propose that we allow
> >
> > listArray (length xs) (xs ++ _|_) = _|_>
>
> given that
>         listArray (1,3) xs = listArray (1,3) (take 3 (xs))
> and take can fuse with a good producer (can it?), I would expect that
> listArray can be made to fuse as good or as bad as take.
>
> What precisely is the problem with the more lazy listArray?
>
> Greetings,
> Joachim
>
>
>
>
>
> --
> Joachim “nomeata” Breitner
>   mail at joachim-breitner.de • http://www.joachim-breitner.de/
>   Jabber: nomeata at joachim-breitner.de  • GPG-Key: 0xF0FBF51F
>   Debian Developer: nomeata at debian.org
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/libraries/attachments/20141113/74da1952/attachment-0001.html>