Re: [Haskell-cafe] a minor bug (memory leak) in ListLike package
On Wed, Aug 24, 2011 at 3:47 PM, Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com wrote:
I was just trying to remember some of the tricks Daniel Peebles (aka
{co}pumpkin) used to do in #haskell with Data.List.genericLength.
I've never really used ListLike, but was just trying to guess why the
default implementation was as it is.
Maybe he used lazy implementations of Num and Ord in combination with
a definition like
length [] = 0
length (_:xs) = 1 + length xs
But as John observed, the accumulating version of length does not
provide such laziness and the accumulator might as well be made
strict.
Sebastian
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Re: [Haskell-cafe] a minor bug (memory leak) in ListLike package
On 24 August 2011 15:54, Sebastian Fischer fisc...@nii.ac.jp wrote:
I _think_ this may cause problems with some data types (e.g.
http://hackage.haskell.org/packages/archive/numbers/2009.8.9/doc/html/Data-Number-Natural.html
) that require the extra laziness (that is, you can do things like ` 3
genericLength [1..] ' and have it return True).
Does the current version support this? The use of an accumulator (that
is presumably returned after consuming the complete input) seems to
suggest that your example would diverge anyway (but I did not try).
I was just trying to remember some of the tricks Daniel Peebles (aka
{co}pumpkin) used to do in #haskell with Data.List.genericLength.
I've never really used ListLike, but was just trying to guess why the
default implementation was as it is.
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] a minor bug (memory leak) in ListLike package
Thanks for reporting this. I understand the problem, however I don't want to bloat the interface even more with a bunch of strict versions of functions. Even so, the current implementation is definitely the worst possible option as it has the slow performance of building thunks without the actual benefits of laziness. `Data.List` currently uses a fully lazy implementation, with RULEs to specialize to a strict variant for Int and Integer accumulators. The same solution should work for ListLike, with the following additions: 1. `length` be made fully strict in the accumulator 2. `genericLength'` (strict variant) be exposed via the interface Currently I know of no way to automatically derive listlike-instances, however the `listlike-instances` package has instances for a few other useful types (vectors and Text mainly). Adding instances is definitely a pain, so I may well try to create a Derive extension for the next time I want to do so. Cheers, John On Wed, Aug 24, 2011 at 5:17 AM, bob zhang bobzhang1...@gmail.com wrote: 于 11-8-23 下午11:37, Ivan Lazar Miljenovic 写道: It might not be what_you_ want, but it might be what others want. If you're concerned with efficiency, then wouldn't you use length rather than genericLength? length is identical to genericLength in ListLike except type signature. but still, import Data.Number import Data.List import qualified Data.ListLike as L (3 :: Natural) genericLength [1..] (work) (3 :: Natural) L.genericLength [1..] (non-terminating) If you want laziness, L.genericLength should be defined like this L.genericLength [] = 0 L.genericLength (_:l) = 1 + L.genericLength l the genericLength used in ListLike package used tail recursion while non-strict. and also, a strict length is still needed (currently, length is identical to genericLength) Thank you bob ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] a minor bug (memory leak) in ListLike package
On Wed, Aug 24, 2011 at 7:47 AM, Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com wrote:
I was just trying to remember some of the tricks Daniel Peebles (aka
{co}pumpkin) used to do in #haskell with Data.List.genericLength.
I've never really used ListLike, but was just trying to guess why the
default implementation was as it is.
Unfortunately I can't answer this either (although I can make a good
guess); it's from John Goerzen's original code. And really, any
thanks for ListLike should go to him; he did all the work.
John L.
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[Haskell-cafe] a minor bug (memory leak) in ListLike package
Hi, John, there is a space leak problem in ListLike typeclass,
in the method genericLength
calclen !accum cl =
calclen accum cl =
--- thank you for your nice library
btw, is there any way to derive ListLike interface automatically?
for such type :
newtype List a = List {[a]}
Best,bob
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Re: [Haskell-cafe] a minor bug (memory leak) in ListLike package
On 24 August 2011 11:10, bob zhang bobzhang1...@gmail.com wrote:
Hi, John, there is a space leak problem in ListLike typeclass,
in the method genericLength
calclen !accum cl =
calclen accum cl =
I _think_ this may cause problems with some data types (e.g.
http://hackage.haskell.org/packages/archive/numbers/2009.8.9/doc/html/Data-Number-Natural.html
) that require the extra laziness (that is, you can do things like ` 3
genericLength [1..] ' and have it return True).
--- thank you for your nice library
btw, is there any way to derive ListLike interface automatically?
for such type :
newtype List a = List {[a]}
GeneralizedNewtypeDeriving can do that.
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] a minor bug (memory leak) in ListLike package
Hi,
I think 3 genericLength [1..] should fail, that laziness is not we
want.
I can not derive ListLike instance using GHC extensions, can you provide
a working example?
Thanks
On Tue, Aug 23, 2011 at 9:47 PM, Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com wrote:
On 24 August 2011 11:10, bob zhang bobzhang1...@gmail.com wrote:
Hi, John, there is a space leak problem in ListLike typeclass,
in the method genericLength
calclen !accum cl =
calclen accum cl =
I _think_ this may cause problems with some data types (e.g.
http://hackage.haskell.org/packages/archive/numbers/2009.8.9/doc/html/Data-Number-Natural.html
) that require the extra laziness (that is, you can do things like ` 3
genericLength [1..] ' and have it return True).
--- thank you for your nice library
btw, is there any way to derive ListLike interface automatically?
for such type :
newtype List a = List {[a]}
GeneralizedNewtypeDeriving can do that.
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
--
Best, bob
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Re: [Haskell-cafe] a minor bug (memory leak) in ListLike package
On 8/23/11 11:17 PM, bob zhang wrote: I think 3 genericLength [1..] should fail, that laziness is not we want. And it'd be more efficient to use lengthBound 3 () [1..] where lengthBound is from list-extras:Data.List.Extras.LazyLength. The efficiency comes from using Int rather than a chain of pointers for lazy Peano numbers. -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] a minor bug (memory leak) in ListLike package
On Wed, Aug 24, 2011 at 10:47 AM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: On 24 August 2011 11:10, bob zhang bobzhang1...@gmail.com wrote: Hi, John, there is a space leak problem in ListLike typeclass, in the method genericLength calclen !accum cl = calclen accum cl = I _think_ this may cause problems with some data types (e.g. http://hackage.haskell.org/packages/archive/numbers/2009.8.9/doc/html/Data-Number-Natural.html ) that require the extra laziness (that is, you can do things like ` 3 genericLength [1..] ' and have it return True). Does the current version support this? The use of an accumulator (that is presumably returned after consuming the complete input) seems to suggest that your example would diverge anyway (but I did not try). Sebastian ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
