Meacham's JHC was headed towards region inference for a while (and may still be), and I spent some time trying to use region inference in a research compiler of my own, and I think both projects effectively came to that same conclusion -- regions and laziness don't mix. Finding useful regions in a lazy language is hard.
You can't effectively annotate them in the source due to laziness decoupling object lifetimes from that of your source stack frames, so you need to infer them once you've translated into some strict intermediate representation, and the regions you can infer are finicky and brittle at best. Region-based code optimization in ML tends to center around identifying which region is leaking and why, and without any sort of source code tie for the region system, that becomes a seriously black box. Thunks tend to hold onto lots of context, so minor source changes yield vastly different region profiles. Finally, all of the effort is called into question by the fact that regions alone can't even handle a lot of interesting cases, so you need a collector to boot. Tofte et al. wrote a retrospective at some point basically talking about the now-known limitations of region based memory management [ http://portal.acm.org/citation.cfm?id=993040 , pre-print: http://www.elsman.com/retro.pdf], which I think has the right balance of optimism and pragmatism where it comes to region-based memory management and talks about many of these issues. -Edward Kmett On Thu, Aug 6, 2009 at 3:22 AM, Simon Peyton-Jones <simo...@microsoft.com>wrote: > Also region inference is likely to be much less effective in a lazy > language, because (I think that) data escapes the lifetime of its allocating > procedure much more often. I don't know of any work that has even tried it. > > Simon > > | -----Original Message----- > | From: haskell-boun...@haskell.org [mailto:haskell-boun...@haskell.org] > On > | Behalf Of Simon Marlow > | Sent: 04 August 2009 14:50 > | To: Sam Martin > | Cc: Colin Runciman; Haskell@haskell.org > | Subject: Re: [Haskell] memory management > | > | On 04/08/2009 13:33, Sam Martin wrote: > | >> Sounds like region inference to me. > | >> (https://secure.wikimedia.org/wikipedia/en/wiki/Region_inference) > | > > | > Thanks, yes, that's exactly what I had in mind. > | > > | > Is anything like this is done in GHC? > | > | Not at the moment, no. > | > | Bear in mind that with generational GC, allocating memory that quickly > | becomes garbage is quite cheap. > | > | Cheers, > | Simon > | _______________________________________________ > | Haskell mailing list > | Haskell@haskell.org > | http://www.haskell.org/mailman/listinfo/haskell > > > _______________________________________________ > Haskell mailing list > Haskell@haskell.org > http://www.haskell.org/mailman/listinfo/haskell > >
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