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Today's Topics:
1. Re: Unmaybe (Kim-Ee Yeoh)
2. Re: How to improve lazyness of a foldl (and memory
footprint) (Giacomo Tesio)
3. Re: Unmaybe (Adrian May)
4. Re: Unmaybe (Brent Yorgey)
5. find by (Julian Arni)
----------------------------------------------------------------------
Message: 1
Date: Wed, 15 May 2013 19:22:28 +0700
From: Kim-Ee Yeoh <[email protected]>
Subject: Re: [Haskell-beginners] Unmaybe
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Message-ID:
<capy+zdqird26r9f8ozfqndali57wgve27_ipskxvqhoyzo0...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
On Wed, May 15, 2013 at 9:58 AM, Adrian May
<[email protected]>wrote:
> The list indices ati and bti are used only once: to retrieve the (first)
>> item matching the predicate. Might Data.List.find be a better fit?
>>
>
> No, I use them via t1 and t2 to figure out which row to put the squiggle
> on. The attached picture might put it all in perspective.
>
>>
D'oh. Didn't see the later references, sorry.
Something to think about is: how would you document "my coordinate system"
as you wrote in your comment? Highly visual things like these are
challenging to describe even for verbal-thinking types.
Probably sticking the picture in png/pdf format and linking to it in the
comments is a good a solution as any.
-- Kim-Ee
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Message: 2
Date: Wed, 15 May 2013 14:55:43 +0200
From: Giacomo Tesio <[email protected]>
Subject: Re: [Haskell-beginners] How to improve lazyness of a foldl
(and memory footprint)
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Message-ID:
<CAHL7psE9goobH6ssPGnQKG5wcaS-zhiRrQjmOM=6y-qay35...@mail.gmail.com>
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Turned out that I didn't need fold at all, just a proper groupBy.
As for these lines
module Main (
>
> main
>
> ) where
>
>
they were generated by Leksah. Do you suggest to remove them? And what
about Leksah as an IDE: do you use it?
Giacomo
On Wed, May 15, 2013 at 9:35 AM, Giacomo Tesio <[email protected]> wrote:
> Thanks a lot!
>
> Yesterday on freenode's #haskell channel Cane noted how my laziness
> problem reside in the foldl use in foldTradingSample.
> I have to turn it into a foldr (but I'm still unsure how...)
>
>
> Giacomo
>
>
> On Wed, May 15, 2013 at 12:46 AM, Henk-Jan van Tuyl <[email protected]>wrote:
>
>> On Tue, 14 May 2013 11:22:27 +0200, Giacomo Tesio <[email protected]>
>> wrote:
>>
>> Hi, I'm trying to improve a small haskell program of mine.
>>>
>> :
>>
>> Some remarks:
>>
>> 0) Use hlint (available on Hackage) for improvement suggestions
>> 1) You don't have to write the module heading in Main.hs, it is not a
>> library (why export main?)
>> 2) Change "print" to "putStrLn" if you want to display messages without
>> quotes
>> 2) switchArgs is only partially defined, add something like:
>> switchArgs [x] = putStrLn $ "Unknown tool: " ++ x
>> 3) Use shorter lines, for example change:
>>
>> importTrades outDir csvFile = transformFile csvFile (foldTradingSample.
>> **getTickWriteTrades) (saveTradingSamples outDir)
>>
>> to:
>>
>> importTrades outDir csvFile =
>> transformFile
>> csvFile
>> (foldTradingSample.**getTickWriteTrades)
>> (saveTradingSamples outDir)
>> 4) It is considered good practice, to write the function
>> composition operator between spaces (change f.g to f . g)
>>
>> I have analyze your software further to see how sufficient laziness can
>> be reached.
>>
>> Regards,
>> Henk-Jan van Tuyl
>>
>>
>> --
>> Folding@home
>> What if you could share your unused computer power to help find a cure?
>> In just 5 minutes you can join the world's biggest networked computer and
>> get us closer sooner. Watch the video.
>> http://folding.stanford.edu/
>>
>>
>> http://Van.Tuyl.eu/
>> http://members.chello.nl/**hjgtuyl/tourdemonad.html<http://members.chello.nl/hjgtuyl/tourdemonad.html>
>> Haskell programming
>> --
>>
>> ______________________________**_________________
>> Beginners mailing list
>> [email protected]
>> http://www.haskell.org/**mailman/listinfo/beginners<http://www.haskell.org/mailman/listinfo/beginners>
>>
>
>
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Message: 3
Date: Wed, 15 May 2013 22:37:56 +0800
From: Adrian May <[email protected]>
Subject: Re: [Haskell-beginners] Unmaybe
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Message-ID:
<cad-ubzfnk8sfm8qgr_nuyndjonczq46y-l2ophpaccgmpgd...@mail.gmail.com>
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I seem to have come up with something:
main = putStrLn $ show $
"Foo".:.100 |:|
"Bar".:.10 >:> (
"Ket".:.20 >^> "Pod".:.1 |^|
"Zig".:.30
) >:> "Erm".:.15
>@> "Nuk".:.50
>@> "Din".:.30
says:
1:Foo=0.0->100.0
2:Bar=0.0->10.0
3:Ket=10.0->30.0
4:Pod=30.0->31.0
5:Zig=10.0->40.0
6:Erm=40.0->55.0
7:Nuk=31.0->81.0
8:Din=30.0->60.0
I'd best give names to those forks though otherwise the whole project plan
will break whenever I insert a new one. Can I give a parameter to an
operator? Like:
task1 `fork "name"` taskb
or:
task1 ( >^> "name" ) taskb
Adrian.
On 15 May 2013 20:22, Kim-Ee Yeoh <[email protected]> wrote:
> On Wed, May 15, 2013 at 9:58 AM, Adrian May <
> [email protected]> wrote:
>
>> The list indices ati and bti are used only once: to retrieve the (first)
>>> item matching the predicate. Might Data.List.find be a better fit?
>>>
>>
>> No, I use them via t1 and t2 to figure out which row to put the squiggle
>> on. The attached picture might put it all in perspective.
>>
>>>
> D'oh. Didn't see the later references, sorry.
>
> Something to think about is: how would you document "my coordinate system"
> as you wrote in your comment? Highly visual things like these are
> challenging to describe even for verbal-thinking types.
>
> Probably sticking the picture in png/pdf format and linking to it in the
> comments is a good a solution as any.
>
> -- Kim-Ee
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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Message: 4
Date: Wed, 15 May 2013 11:19:54 -0400
From: Brent Yorgey <[email protected]>
Subject: Re: [Haskell-beginners] Unmaybe
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
On Wed, May 15, 2013 at 10:37:56PM +0800, Adrian May wrote:
>
> I'd best give names to those forks though otherwise the whole project plan
> will break whenever I insert a new one. Can I give a parameter to an
> operator? Like:
>
> task1 `fork "name"` taskb
>
> task1 ( >^> "name" ) taskb
No, unfortunately neither of those is possible.
-Brent
------------------------------
Message: 5
Date: Wed, 15 May 2013 12:11:19 -0400
From: Julian Arni <[email protected]>
Subject: [Haskell-beginners] find by
To: [email protected]
Message-ID:
<CANct4CQyD7-ECb8VK+Dv=T3DRp9P=b4yce_jznm8u0zfkvo...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
I have a function that, simplifying a little, looks like this:
fn :: [a] -> a
fn = (head .) . takeWhile $ (\_ -> True)
>From this, I want a function with the signature fn' :: [(x,a)] -> (x,a)
such that:
snd $ fn' (zip [x] [a]) = fn [a]
I can see ways of doing this by altering fn, or by repeating some of fn in
the definition of fn', or (because in this case I know that if fn xs = x,
fn is returning the first x in xs and not any others), by doing something
nasty like:
fn' xs = xs !! fromMaybe 0 (findIndex (\(_,a) -> a == fn (snd $ unzip
xs)) xs )
But it seems to me like there should be prettier solutions to this (that *do
not* involve changing the definition of fn). After all, this doesn't seem
like a rare pattern.
Anyone know if in fact there's a better way to go about it?
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