[Haskell-cafe] Memory Management and Lists

[Matthew Bray]

https://www.schoolofhaskell.com/user/edwardk/snippets/once

Cool trick :)

On Thu, 14 Jul 2016 at 08:56 Tom Ellis <
tom-lists-haskell-cafe-2013 at jaguarpaw.co.uk> wrote:

> Yes, this is a very neat trick and very effective.  (I couldn't acutally
> find it on Hoogle.  Does anyone have a link?)
>
> On Thu, Jul 14, 2016 at 07:45:33AM +0000, Robin Palotai wrote:
> > For deepseq also see the"Once trick". I'm surprised it's not quoted more
> > often. In fact our would make sense to mention it in the deepseq docs.
> >
> > On Wed, Jul 13, 2016, 21:32 David Feuer <david.feuer at gmail.com> wrote:
> >
> > > You have to be careful with deepseq. Using it in the wrong place can
> > > lead to very bad performance. It's a big hammer. Its blow can
> > > sometimes be softened using the NF type from the nf package, but it's
> > > really not the right thing most of the time.
> > >
> > > On Tue, Jul 12, 2016 at 11:56 PM, William Yager <will.yager at gmail.com>
> > > wrote:
> > > > You probably want Control.DeepSeq. No extraneous work doing addition
> that
> > > > way either.
> > > >
> > > > Will
> > > >
> > > > On Tue, Jul 12, 2016 at 11:28 PM, Christopher Howard <
> ch.howard at zoho.com
> > > >
> > > > wrote:
> > > >>
> > > >> After pondering this problem some more, I found a solution to the
> > > >> problem was to introduce strictness, not deep down in the
> StateReader
> > > >> monad, but rather at the top level, i.e., forcing evaluation of each
> > > >> Matrix as soon as it is pulled of the list of Matrices. I found I
> could
> > > >> do this simply by summing all the elements in each matrix and
> printing
> > > >> the sum to std out. With this approach, i successfully run the full
> > > >> program and never even saw my memory performance graph move up.
> > > >>
> > > >> I suppose there might be a way to do the same thing more efficiently
> > > >> with seq...?
> > > >>
> > > >> On 07/12/2016 06:39 PM, Christopher Howard wrote:
> > > >> > I guess I was hesitating on posting the entire program source
> code in
> > > an
> > > >> > cafe email. I suppose I could send you a tarball, if you really
> wanted
> > > >> > it...
> > > >> >
> > > >> > Matrix is from Data.Matrix
> > > >> >
> > > >> > <
> > >
> http://hackage.haskell.org/package/matrix-0.3.5.0/docs/Data-Matrix.html>.
> > > >> >
> > > >> > It is hard to understand how thunks alone would explain it...
> there
> > > >> > would be at most 2000 thunks, right? Unless... Could there be a
> thunk
> > > >> > for every single call to getElem? That would be a lot of thunks!
> > > >> >
> > > >> > Somebody suggested adding some strictness here... could you
> elaborate
> > > on
> > > >> > that? I tried inserting seq, but I didn't really understand how I
> was
> > > >> > supposed to use it...
> > > >> >
> > > >>
> > > >> --
> > > >> http://qlfiles.net
> > > >> To protect my privacy, please use PGP encryption. It's free and easy
> > > >> to use! My public key ID is 0x340EA95A (pgp.mit.edu).
> > > >>
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> > > >
> > > >
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