[Haskell-cafe] Memory Management and Lists

[Lian Hung Hon]

I faced the same problem in an RWS monad, where adding a print to the
evalRWS resolves the space leak. Obviously, it's not very elegant to
clutter the output. I tried the unsafeInterleaveIO (works sometimes),
seq/deepseq (works on Windows but not on Linux??), strictness annotations
(didn't seem to help at all?), but finally settled on using pipes/conduit.
It's remarkable how a streaming library is more practical than the
language's core feature - laziness.

On 14 July 2016 at 16:32, Matthew Bray <mattjbray at gmail.com> wrote:

> 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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