[Haskell-cafe] hdbc parametrized select
does hdbc have parametrized selects ? There is execute execute :: Statement - [SqlValue] - IO Integer and some other functions which get list of parameters but return IO Integer or IO () and there is other couple of functions fetchRow :: Statement - IO (Maybe [SqlValue]) which return values of select but do not get parameters How can i execute parametrized select with hdbc ? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] tplot (out of memory)
Did you ever solve this? I have a similar message ( user error (out of memory) ) arising from a different app (not tplot) that uses the Haskell Chart library (and cairo underneath). On some linux machines, it crashes, on others it works fine. I can find no environment differences between the machines. The app does not use a lot of memory, and the machine is not running out of physical or swap.Regards, MalcolmOn 04 Sep, 2012,at 04:01 PM, Eugene Kirpichov ekirpic...@gmail.com wrote:Hi Manish, Please provide the input file, I'll debug this. On Mon, Sep 3, 2012 at 1:06 PM, Manish Trivedi trivman...@gmail.com wrote: Hi, I am running into a weird out of memory issue. While running timeplot over an input file having ~800 rows. From below provided info, seems like machine has enough ram (1849MB). Please let me know if anyone has pointers. # free -m total used free shared buffers cached Mem: 3825 1975 1849 0 13 71 -/+ buffers/cache: 1891 1934 Swap: 4031 111 3920 #time tplot -o out.png -or 1024x768 -k 'CurrentPerHour' 'lines' -k 'RequiredPerHour' 'lines' -if adgroup_delivery_chart.input -tf 'date %Y-%m-%d %H:%M:%OS' tplot: user error (out of memory) real 0m0.026s user 0m0.018s sys 0m0.008s -Manish ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Eugene Kirpichov http://www.linkedin.com/in/eugenekirpichov ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How to correctly benchmark code with Criterion?
Dear list, during past few days I spent a lot of time trying to figure out how to write Criterion benchmarks, so that results don't get skewed by lazy evaluation. I want to benchmark different versions of an algorithm doing numerical computations on a vector. For that I need to create an input vector containing a few thousand elements. I decided to create random data, but that really doesn't matter - I could have as well use infinite lists instead of random ones. My problem is that I am not certain if I am creating my benchmark correctly. I wrote a function that creates data like this: dataBuild :: RandomGen g = g - ([Double], [Double]) dataBuild gen = (take 6 $ randoms gen, take 2048 $ randoms gen) And I create benchmark like this: bench Lists $ nf L.benchThisFunction (L.dataBuild gen) The question is how to generate data so that its evaluation won't be included in the benchmark. I already asked this question on StackOverflow ( http://stackoverflow.com/questions/12896235/how-to-create-data-for-criterion-benchmarks#comment17466915_12896235 ) and got answer to use evaluate + force. After spending one day on testing this approach I came to conclusion that doing this does not seem to influence results of a benchmark in any way (I did stuf like unsagePerformIO + delayThread). On the other hand I looked into sources of criterion and I see that the benchmark code is run like this: evaluate (rnf (f x)) I am a Haskell newbie and perhaps don't interpret this correctly, but to me it looks as though criterion did not evaluate the possibly non-evaluated parameter x before running the benchmark, but instead evaluates the final result. Can someone provide an explanation on how this exactly works and how should I write my benchmarks so that results are correct? Janek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to correctly benchmark code with Criterion?
Hi Janek, On 18/10/12 10:23, Janek S. wrote: during past few days I spent a lot of time trying to figure out how to write Criterion benchmarks, so that results don't get skewed by lazy evaluation. I want to benchmark different versions of an algorithm doing numerical computations on a vector. For that I need to create an input vector containing a few thousand elements. I decided to create random data, but that really doesn't matter - I could have as well use infinite lists instead of random ones. [snip] The question is how to generate data so that its evaluation won't be included in the benchmark. Something like this might work, not sure what the canonical way is. ---8--- main = do ... let input = L.dataBuild gen evaluate (rnf input) defaultMain ... bench Lists $ nf L.benchThisFunction input ... ---8--- I did use something like this in practice here: https://gitorious.org/bitwise/bitwise/blobs/master/extra/benchmark.hs#line155 Thanks, Claude -- http://mathr.co.uk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to correctly benchmark code with Criterion?
I don't know if you have already read them, but Tibell's slides on High Performance Haskell are pretty good: http://www.slideshare.net/tibbe/highperformance-haskell There is a section at the end where he runs several tests using Criterion. HTH, A. On 18 October 2012 11:45, Claude Heiland-Allen cla...@mathr.co.uk wrote: Hi Janek, On 18/10/12 10:23, Janek S. wrote: during past few days I spent a lot of time trying to figure out how to write Criterion benchmarks, so that results don't get skewed by lazy evaluation. I want to benchmark different versions of an algorithm doing numerical computations on a vector. For that I need to create an input vector containing a few thousand elements. I decided to create random data, but that really doesn't matter - I could have as well use infinite lists instead of random ones. [snip] The question is how to generate data so that its evaluation won't be included in the benchmark. Something like this might work, not sure what the canonical way is. ---8--- main = do ... let input = L.dataBuild gen evaluate (rnf input) defaultMain ... bench Lists $ nf L.benchThisFunction input ... ---8--- I did use something like this in practice here: https://gitorious.org/bitwise/**bitwise/blobs/master/extra/** benchmark.hs#line155https://gitorious.org/bitwise/bitwise/blobs/master/extra/benchmark.hs#line155 Thanks, Claude -- http://mathr.co.uk __**_ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/**mailman/listinfo/haskell-cafehttp://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Fwd: hdbc parametrized select
This was not sent to the cafe since I used the wrong from address. -- Forwarded message -- From: Asten, W.G.G. van (Wilfried, Student M-CSC) w.g.g.vanas...@student.utwente.nl Date: Thu, Oct 18, 2012 at 12:27 PM Subject: Re: [Haskell-cafe] hdbc parametrized select To: s9gf4...@gmail.com Cc: haskell-cafe@haskell.org To my knowledge you can combine execute and the fetch functions like this: find conn id = do stmt - prepare conn SELECT * FROM table WHERE id = ? LIMIT 1 excute stmt [id] row - fetchRow stmt On Thu, Oct 18, 2012 at 10:51 AM, s9gf4...@gmail.com wrote: does hdbc have parametrized selects ? There is execute execute :: Statement - [SqlValue] - IO Integer and some other functions which get list of parameters but return IO Integer or IO () and there is other couple of functions fetchRow :: Statement - IO (Maybe [SqlValue]) which return values of select but do not get parameters How can i execute parametrized select with hdbc ? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] A yet another question about subtyping and heterogeneous collections
Hello list!
I've been experimenting with emulating subtyping and heterogeneous
collections in Haskell. I need this to parse a binary representation of
objects of a class hierarchy in C++ program.
So far I implemented upcasting using a chain of type classes and now I'm
playing with heterogeneous lists. For future purposes It would be ideal
to be able to have something like these functions:
upcast_list :: [LikeC] - [LikeA]
downcast_list :: [LikeA] - [LikeC]
First one only replaces the existential wrapper leaving the actual value
intact, and the second one also filters the list, passing the elements
with specific enough type.
I can implement this particular functions, but what's about a more
general one? Something like cast_list :: [a] - [b], where a and b are
existential types from one hierarchy. Something like LikeA and LikeC in
my example.
Is my approach feasible? Is there a better one? Am I missing something
obvious?
Any relevant advices are welcome.
The example code follows:
{-# LANGUAGE FlexibleInstances, UndecidableInstances,
OverlappingInstances, ExistentialQuantification, DeriveDataTypeable #-}
import Data.Typeable
import Data.Maybe
data A = A {a_x :: Int} deriving (Show, Typeable)
data B = B {b_x :: Int, b_a :: A} deriving (Show, Typeable)
data C = C {c_z :: Int, c_b :: B} deriving (Show, Typeable)
data D = D {d_w :: Int, d_c :: C, d_a :: A} deriving (Show, Typeable)
class ALike x where toA :: x - A
class BLike x where toB :: x - B
class CLike x where toC :: x - C
class DLike x where toD :: x - D
instance ALike A where toA = id
instance BLike B where toB = id
instance CLike C where toC = id
instance DLike D where toD = id
instance ALike B where toA = b_a
instance BLike C where toB = c_b
instance CLike D where toC = d_c
instance (BLike x) = (ALike x) where
toA = (toA :: B - A) . toB
instance CLike x = BLike x where
toB = toB . toC
a1 = A 1
b1 = B 2 (A 2)
c1 = C 3 b1
d1 = D 4 c1 (A 10)
print_a :: ALike x = x - String
print_a v = A = ++ show (a_x $ toA v)
sum_a :: (ALike x, ALike y) = x - y - String
sum_a v1 v2 = A1 = ++ show (a_x $ toA v1) ++ A2 = ++ show (a_x $
toA v2)
data LikeA = forall a. (ALike a, Typeable a) = LikeA a
instance ALike LikeA where
toA (LikeA x) = toA x
get_mono :: Typeable b = [LikeA] - [b]
get_mono = catMaybes . map ((\(LikeA x) - cast x))
data LikeC = forall c. (CLike c, Typeable c) = LikeC c
instance CLike LikeC where
toC (LikeC x) = toC x
lst_a = [LikeA a1, LikeA b1, LikeA c1, LikeA d1]
lst_c = [LikeC c1, LikeC d1]
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A yet another question about subtyping and heterogeneous collections
Why do you need ALike x, BLike x etc.? Why not just Like u x?
Отправлено с iPhone
Oct 18, 2012, в 14:36, Dmitry Vyal akam...@gmail.com написал(а):
Hello list!
I've been experimenting with emulating subtyping and heterogeneous
collections in Haskell. I need this to parse a binary representation of
objects of a class hierarchy in C++ program.
So far I implemented upcasting using a chain of type classes and now I'm
playing with heterogeneous lists. For future purposes It would be ideal to be
able to have something like these functions:
upcast_list :: [LikeC] - [LikeA]
downcast_list :: [LikeA] - [LikeC]
First one only replaces the existential wrapper leaving the actual value
intact, and the second one also filters the list, passing the elements with
specific enough type.
I can implement this particular functions, but what's about a more general
one? Something like cast_list :: [a] - [b], where a and b are existential
types from one hierarchy. Something like LikeA and LikeC in my example.
Is my approach feasible? Is there a better one? Am I missing something
obvious?
Any relevant advices are welcome.
The example code follows:
{-# LANGUAGE FlexibleInstances, UndecidableInstances, OverlappingInstances,
ExistentialQuantification, DeriveDataTypeable #-}
import Data.Typeable
import Data.Maybe
data A = A {a_x :: Int} deriving (Show, Typeable)
data B = B {b_x :: Int, b_a :: A} deriving (Show, Typeable)
data C = C {c_z :: Int, c_b :: B} deriving (Show, Typeable)
data D = D {d_w :: Int, d_c :: C, d_a :: A} deriving (Show, Typeable)
class ALike x where toA :: x - A
class BLike x where toB :: x - B
class CLike x where toC :: x - C
class DLike x where toD :: x - D
instance ALike A where toA = id
instance BLike B where toB = id
instance CLike C where toC = id
instance DLike D where toD = id
instance ALike B where toA = b_a
instance BLike C where toB = c_b
instance CLike D where toC = d_c
instance (BLike x) = (ALike x) where
toA = (toA :: B - A) . toB
instance CLike x = BLike x where
toB = toB . toC
a1 = A 1
b1 = B 2 (A 2)
c1 = C 3 b1
d1 = D 4 c1 (A 10)
print_a :: ALike x = x - String
print_a v = A = ++ show (a_x $ toA v)
sum_a :: (ALike x, ALike y) = x - y - String
sum_a v1 v2 = A1 = ++ show (a_x $ toA v1) ++ A2 = ++ show (a_x $ toA
v2)
data LikeA = forall a. (ALike a, Typeable a) = LikeA a
instance ALike LikeA where
toA (LikeA x) = toA x
get_mono :: Typeable b = [LikeA] - [b]
get_mono = catMaybes . map ((\(LikeA x) - cast x))
data LikeC = forall c. (CLike c, Typeable c) = LikeC c
instance CLike LikeC where
toC (LikeC x) = toC x
lst_a = [LikeA a1, LikeA b1, LikeA c1, LikeA d1]
lst_c = [LikeC c1, LikeC d1]
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to correctly benchmark code with Criterion?
Something like this might work, not sure what the canonical way is. (...) This is basically the same as the answer I was given on SO. My concerns about this solutions are: - rnf requires its parameter to belong to NFData type class. This is not the case for some data structures like Repa arrays. - evaluate only evaluates its argument to WHNF - is this enough? If I have a tuple containing two lists won't this only evaluate the tuple construtor and leave the lists as thunks? This is actually the case in my code. As I said previously, it seems that Criterion somehow evaluates the data so that time needed for its creation is not included in the benchmark. I modified my dataBuild function to look lik this: dataBuild gen = unsafePerformIO $ do let x = (take 6 $ randoms gen, take 2048 $ randoms gen) delayThread 100 return x When I ran the benchmark, criterion estimated the time needed to complete it to over 100 seconds (which means that delayThread worked and was used as a basis for estimation), but the benchamrk was finished much faster and there was no difference in the final result comparing to the normal dataBuild function. This suggests that once data was created and used for estimation, the dataBuild function was not used again. The main question is: is this observation correct? In this question on SO: http://stackoverflow.com/questions/6637968/how-to-use-criterion-to-measure-performance-of-haskell-programs one of the aswers says that there is no automatic memoization, while it looks that in fact the values of dataBuild are memoized. I have a feeling that I am misunderstanding something. I don't know if you have already read them, but Tibell's slides on High Performance Haskell are pretty good: http://www.slideshare.net/tibbe/highperformance-haskell There is a section at the end where he runs several tests using Criterion. I skimmed the slides and slide 59 seems to show that my concerns regarding WHNF might be true. Janek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A yet another question about subtyping and heterogeneous collections
On 10/18/2012 03:20 PM, MigMit wrote:
Why do you need ALike x, BLike x etc.? Why not just Like u x?
Hmm, looks like a nice idea. I tried it, unfortunately I can't cope with
compiler error messages:
tst.hs:32:15:
Context reduction stack overflow; size = 201
Use -fcontext-stack=N to increase stack size to N
Upcast a b
In the first argument of `(.)', namely `(upcast :: b - a)'
In the expression: (upcast :: b - a) . (upcast :: c - b)
In the expression: (upcast :: b - a) . (upcast :: c - b) $ x
{-# LANGUAGE FlexibleInstances, UndecidableInstances,
OverlappingInstances, ExistentialQuantification, DeriveDataTypeable,
MultiParamTypeClasses, FlexibleContexts,
IncoherentInstances #-}
import Data.Typeable
import Data.Maybe
data A = A {a_x :: Int} deriving (Show, Typeable)
data B = B {b_x :: Int, b_a :: A} deriving (Show, Typeable)
data C = C {c_z :: Int, c_b :: B} deriving (Show, Typeable)
data D = D {d_w :: Int, d_c :: C, d_a :: A} deriving (Show, Typeable)
class Upcast c x where
upcast :: x - c
instance Upcast x x where
upcast = id
instance Upcast A B where upcast = b_a
instance Upcast B C where upcast = c_b
instance Upcast C D where upcast = d_c
instance (Upcast a b, Upcast b c) = Upcast a c where
upcast = (upcast :: b - a) . (upcast :: c - b)
a1 = A 1
b1 = B 2 (A 2)
c1 = C 3 b1
d1 = D 4 c1 (A 10)
print_a :: Upcast A x = x - String
print_a v = A = ++ show (a_x $ upcast v)
sum_a :: (Upcast A x, Upcast A y) = x - y - String
sum_a v1 v2 = A1 = ++ show (a_x $ upcast v1) ++ A2 = ++ show (a_x
$ upcast v2)
data LikeA = forall a. (Upcast A a, Typeable a) = LikeA a
--instance Upcast a LikeA where
-- upcast (LikeA x) = upcast x
lst_a = [LikeA a1, LikeA b1, LikeA c1, LikeA d1]
get_mono :: Typeable b = [LikeA] - [b]
get_mono = catMaybes . map ((\(LikeA x) - cast x))
data LikeC = forall c. (Upcast C c, Typeable c) = LikeC c
--instance Upcast C LikeC where
-- upcast (LikeC x) = upcast x
lst_c = [LikeC c1, LikeC d1]
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to correctly benchmark code with Criterion?
On Thu, Oct 18, 2012 at 4:23 AM, Janek S. fremenz...@poczta.onet.pl wrote: Dear list, during past few days I spent a lot of time trying to figure out how to write Criterion benchmarks, so that results don't get skewed by lazy evaluation. I want to benchmark different versions of an algorithm doing numerical computations on a vector. For that I need to create an input vector containing a few thousand elements. I decided to create random data, but that really doesn't matter - I could have as well use infinite lists instead of random ones. My problem is that I am not certain if I am creating my benchmark correctly. I wrote a function that creates data like this: dataBuild :: RandomGen g = g - ([Double], [Double]) dataBuild gen = (take 6 $ randoms gen, take 2048 $ randoms gen) And I create benchmark like this: bench Lists $ nf L.benchThisFunction (L.dataBuild gen) The argument value will be evaluated by the first run of the bench-mark, and then laziness will keep the value around for the next few hundred runs that the bench function performs. So the evaluation will be included in the benchmark, but if bench is doing enough trials it will be statistical noise. Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to correctly benchmark code with Criterion?
So the evaluation will be included in the benchmark, but if bench is doing enough trials it will be statistical noise. When I intentionally delayed my dataBuild function (using delayThread 100) the estimated time of benchmark was incorrect, but when I got the final results all runs were below 50ms, which means that initial run that took 1 second was discarded. So it seems to me that the first evaluation is discarded. Would be good if someone could definitely confirm that. Janek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to correctly benchmark code with Criterion?
On Thu, Oct 18, 2012 at 9:06 AM, Janek S. fremenz...@poczta.onet.pl wrote: So the evaluation will be included in the benchmark, but if bench is doing enough trials it will be statistical noise. When I intentionally delayed my dataBuild function (using delayThread 100) the estimated time of benchmark was incorrect, but when I got the final results all runs were below 50ms, which means that initial run that took 1 second was discarded. So it seems to me that the first evaluation is discarded. Would be good if someone could definitely confirm that. You could email Bryan, the author of criterion. Janek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A yet another question about subtyping and heterogeneous collections
* Dmitry Vyal akam...@gmail.com [2012-10-18 17:31:13+0400] On 10/18/2012 03:20 PM, MigMit wrote: Why do you need ALike x, BLike x etc.? Why not just Like u x? Hmm, looks like a nice idea. I tried it, unfortunately I can't cope with compiler error messages: tst.hs:32:15: Context reduction stack overflow; size = 201 Use -fcontext-stack=N to increase stack size to N Upcast a b In the first argument of `(.)', namely `(upcast :: b - a)' In the expression: (upcast :: b - a) . (upcast :: c - b) In the expression: (upcast :: b - a) . (upcast :: c - b) $ x instance (Upcast a b, Upcast b c) = Upcast a c where upcast = (upcast :: b - a) . (upcast :: c - b) This is the offending instance. Remember, GHC only looks at the instance head (Upcast a c here) when it decides which instance to use. Roman ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Teaching Haskell @ MOOCs like Coursera or Udacity
I am a novice in Haskell but I would love to see the gurus out here teaching Haskell on MOOCs like Coursera or Udacity. Dr Martin Odersky is doing it for Scala here: https://www.coursera.org/course/progfun I would love to see Haskell growing on such new platforms! Regards, Niket ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Teaching Haskell @ MOOCs like Coursera or Udacity
+1 2012/10/18 niket niketku...@gmail.com: I would love to see Haskell growing on such new platforms! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to correctly benchmark code with Criterion?
Yes, Criterion always discards the time of the first evaluation. On 18 October 2012 15:06, Janek S. fremenz...@poczta.onet.pl wrote: So the evaluation will be included in the benchmark, but if bench is doing enough trials it will be statistical noise. When I intentionally delayed my dataBuild function (using delayThread 100) the estimated time of benchmark was incorrect, but when I got the final results all runs were below 50ms, which means that initial run that took 1 second was discarded. So it seems to me that the first evaluation is discarded. Would be good if someone could definitely confirm that. Janek ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Push the envelope. Watch it bend. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to correctly benchmark code with Criterion?
On 18 October 2012 13:15, Janek S. fremenz...@poczta.onet.pl wrote: Something like this might work, not sure what the canonical way is. (...) This is basically the same as the answer I was given on SO. My concerns about this solutions are: - rnf requires its parameter to belong to NFData type class. This is not the case for some data structures like Repa arrays. For unboxed arrays of primitive types WHNF = NF. That is, once the array is constructed all its elements will be in WHNF. - evaluate only evaluates its argument to WHNF - is this enough? If I have a tuple containing two lists won't this only evaluate the tuple construtor and leave the lists as thunks? This is actually the case in my code. That is why you use rnf from the NFData type class. You use evaluate to kick-start rnf which then goes ahead and evaluates everything (assuming the NFData instance has been defined correctly.) As I said previously, it seems that Criterion somehow evaluates the data so that time needed for its creation is not included in the benchmark. I modified my dataBuild function to look lik this: dataBuild gen = unsafePerformIO $ do let x = (take 6 $ randoms gen, take 2048 $ randoms gen) delayThread 100 return x When I ran the benchmark, criterion estimated the time needed to complete it to over 100 seconds (which means that delayThread worked and was used as a basis for estimation), but the benchamrk was finished much faster and there was no difference in the final result comparing to the normal dataBuild function. This suggests that once data was created and used for estimation, the dataBuild function was not used again. The main question is: is this observation correct? In this question on SO: http://stackoverflow.com/questions/6637968/how-to-use-criterion-to-measure-performance-of-haskell-programs one of the aswers says that there is no automatic memoization, while it looks that in fact the values of dataBuild are memoized. I have a feeling that I am misunderstanding something. If you bind an expression to a variable and then reuse that variable, the expression is only evaluated once. That is, in let x = expr in ... the expression is only evaluated once. However, if you have f y = let x = expr in ... then the expression is evaluated once per function call. I don't know if you have already read them, but Tibell's slides on High Performance Haskell are pretty good: http://www.slideshare.net/tibbe/highperformance-haskell There is a section at the end where he runs several tests using Criterion. I skimmed the slides and slide 59 seems to show that my concerns regarding WHNF might be true. It's usually safe if you benchmark a function. However, you most likely want the result to be in normal form. The nf does this for you. So, if your benchmark function has type f :: X - ([Double], Double), your benchmark will be: bench f (nf f input) The first run will evaluate the input (and discard the runtime) and all subsequent runs will evaluate the result to normal form. For repa you can use deepSeqArray [1] if your array is not unboxed: bench f' (whnf (deepSeqArray . f) input) [1]: http://hackage.haskell.org/packages/archive/repa/3.2.2.2/doc/html/Data-Array-Repa.html#v:deepSeqArray ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Getting PID of a child process
Hi All, Using `System.Process.runInteractiveProcess', I can start a process and get a handle to it: runInteractiveProcess :: FilePath - [String] - Maybe FilePath - Maybe [(String, String)] - IO (Handle, Handle, Handle, ProcessHandle) For diagnostic purposes, I'd like to print the PID of the process attached to this handle -- how best to do that? -- Jason Dusek pgp // solidsnack // C1EBC57DC55144F35460C8DF1FD4C6C1FED18A2B ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Getting PID of a child process
On Thu, Oct 18, 2012 at 5:03 PM, Jason Dusek jason.du...@gmail.com wrote: For diagnostic purposes, I'd like to print the PID of the process attached to this handle -- how best to do that? In Mueval when I wanted the PID (so I could later send sigkills), I did this: hdl - runProcess mueval-core args Nothing Nothing Nothing Nothing Nothing _ - forkIO $ do threadDelay (7 * 70) status - getProcessExitCode hdl case status of Nothing - do terminateProcess hdl _ - withProcessHandle hdl (\x - case x of OpenHandle pid - signalProcess 9 pid return (undefined, undefined) _ - return (undefined,undefined)) exitWith (ExitFailure 1) Just a - exitWith a stat - waitForProcess hdl exitWith stat The key is the poorly documented withProcessHandle :: System.Process.Internals.ProcessHandle - (ProcessHandle__ - IO (ProcessHandle__, a)) - IO a The implementation: data ProcessHandle__ = OpenHandle PHANDLE | ClosedHandle ExitCode type PHANDLE = CPid Well, my code seems to work, anyway... -- gwern http://www.gwern.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCE: apphointments - A simple functional calendar
Dear Café, I just wrote myself a small (~ 200 LOC) calendar application today. https://bitbucket.org/rainmaker/apphointments Comments/Patches welcome. From the readme: apphointments - A simple functional calendar This is a UI = Code calendar application: You create an event by writing code that defines it. To see what's up next, you create a report, i.e. a summary of the events in a certain time range such as 'thisWeek'. This is done by haskell functions again from GHCi or ghc -e. See example.hs. Using just haskell instead of our own language or GUI allows great flexibility in both defining events and generating reports. See e.g. the 'lecture' combinator from Apphointments.Util. Status -- Works for me, but has no features yet. See TODO. Credits --- Created by Steffen Schuldenzucker sschuldenzuc...@uni-bonn.de ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Getting PID of a child process
Quoth Jason Dusek jason.du...@gmail.com, Using `System.Process.runInteractiveProcess', I can start a process and get a handle to it: runInteractiveProcess :: FilePath - [String] - Maybe FilePath - Maybe [(String, String)] - IO (Handle, Handle, Handle, ProcessHandle) For diagnostic purposes, I'd like to print the PID of the process attached to this handle -- how best to do that? There's a good chance this isn't the best way, but it seems to work: import System.Process import System.Process.Internals (ProcessHandle__(..), PHANDLE, withProcessHandle) -- for use with withProcessHandle getPID :: ProcessHandle__ - IO (ProcessHandle__, Maybe PHANDLE) getPID h@(OpenHandle t) = return (h, Just t) getPID h@(ClosedHandle t) = return (h, Nothing) main = do (h0, h1, h2, hp) - runInteractiveProcess /bin/date [] Nothing Nothing mp - withProcessHandle hp $ getPID print mp Seems like more scaffolding than this application really ought to require. Donn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A yet another question about subtyping and heterogeneous collections
Roman Cheplyaka roma at ro-che.info writes: * Dmitry Vyal akamaus at gmail.com [2012-10-18 17:31:13+0400] On 10/18/2012 03:20 PM, MigMit wrote: Why do you need ALike x, BLike x etc.? Why not just Like u x? Hmm, looks like a nice idea. I tried it, unfortunately I can't cope with compiler error messages: tst.hs:32:15: Context reduction stack overflow; size = 201 Use -fcontext-stack=N to increase stack size to N Upcast a b In the first argument of `(.)', namely `(upcast :: b - a)' In the expression: (upcast :: b - a) . (upcast :: c - b) In the expression: (upcast :: b - a) . (upcast :: c - b) $ x instance (Upcast a b, Upcast b c) = Upcast a c where upcast = (upcast :: b - a) . (upcast :: c - b) This is the offending instance. Remember, GHC only looks at the instance head (Upcast a c here) when it decides which instance to use. Roman Hi Dmitry, looks like you've got the classic (show . read) difficulty. In your Upcast a c instance, the compiler is trying to figure out the type of b. You might think there's only one 'chain' to get from (say) type A to type D -- that is via Upcast A B to Upcast B C to Upcast C D; but there's also an instance Upcast x x -- which means there could be any number of Upcast A A, Upcast B B, etc links in the chain. (And this doesn't count all the other possible instances that might be defined in other modules -- for all the compiler knows at that point.) The modern way to handle this is using type functions (aka type families aka associated types), but I'm not sure how that would apply here. (And, for the record, the old-fashioned way would use functional dependencies, as per the Heterogenous Collections paper aka 'HList's). AntC ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] acid-state audit trail
Hey all, I've been looking at acid-state as a possible storage backend for an application. It looks like it fits my needs pretty damn well, but one thing that I'm curious about is if it is possible to get a list of update events. You can obviously query for the current state, but it's not immediately apparent if you can see the history of your values state. This is useful in some things, like providing audit trails and debugging. As well as being able to re-create state in a different form. I was also curious if the createCheckpoint function eliminates the state history or does it just create a snapshot, it's not apparent from the docs. Thanks, Rich ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
