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Today's Topics:
1. Re: Code review request? (Akhra Gannon)
2. Re: Code review request? (Julian Camilo Osorio)
3. Parallel Processing in Libraries? (Leonhard Applis)
----------------------------------------------------------------------
Message: 1
Date: Wed, 15 Jan 2020 12:02:04 -0800
From: Akhra Gannon <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Code review request?
Message-ID:
<CAJoPsuAvJGjS1jKARXp8xTwpZo1A2-uDE1OZEazAY=jxxmv...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Also worth noting that Ut's version can be expressed as a fold:
canBalanceElem x acc@(y, z, p) = if p then acc else let y'=y+x; z'=z-x in
(y', z', y'==z')
canBalanceFold xs = (\(_, _, p) -> p) $ foldr canBalanceElem (0, sum xs,
False) xs
On Wed, Jan 15, 2020 at 10:54 AM Ut Primum <[email protected]> wrote:
> Hi,
> this is how I would have solved the exercise:
>
> canBalanceRec [] _ _ = False
> canBalanceRec (x:xs) s1 s2 = s1+x==s2-x || canBalanceRec xs (s1+x) (s2-x)
> canBalance xs = s==0 || canBalanceRec xs 0 s where s=sum xs
>
> Note that there is one difference: in this case
> canBalance [-2,-2,4] = True
> because I think I can split the list into [ ] and the rest (since the sum
> of the empty list is 0 and the same is the sum of the elements of the
> lists). Anyway this is a matter of how we interpret the text of the
> exercise (your function would return False instead). Note that removing the
> "s==0 ||" makes no difference.
>
> An advantage of my solution is that it is less expensive, since its
> computational complexity is linear in the length of the list xs. Yours uses
> sum and drop many times, and so is slower. Just to have an idea of the
> difference (using ghci interpreter):
>
> > canBalance [1..10000]
> False
> (*0.02* secs, 6,974,552 bytes)
> > can_split_even [1..10000]
> False
> (*5.60* secs, 11,395,843,384 bytes)
>
> Cheers,
> Ut
>
> Il giorno mer 15 gen 2020 alle ore 18:27 Jake Vossen <[email protected]> ha
> scritto:
>
>> Hey everyone,
>>
>> Let me know if this is not the right place for this, but I am curious if
>> someone could take a look at my code and maybe share some feedback / how
>> a more experienced haskeller would approach this problem.
>>
>> New to Haskell, pretty experienced with imperative languages. I have
>> solved the following problem in Haskell:
>>
>> > Given a non-empty array, return true if there is a place to split the
>> > array so that the sum of the numbers on one side is equal to the sum
>> > of the numbers on the other side.
>>
>> > canBalance([1, 1, 1, 2, 1]) -> true
>> > canBalance([2, 1, 1, 2, 1]) -> false
>> > canBalance([10, 10]) -> true
>>
>> Here is my code (my solution uses `can_split_even` not `canBalance`)
>>
>> ```
>> can_split_even :: (Num a) => (Eq a) => [a] -> Bool
>> can_split_even xs = True `elem` is_even_at_each_spot
>> where
>> is_even_at_each_spot :: [Bool]
>> is_even_at_each_spot = map (is_split xs) [1 .. (length xs - 1)]
>> where
>> is_split :: (Num a) => (Eq a) => [a] -> Int -> Bool
>> is_split xs index = sum (take index xs) == sum (drop index xs)
>> ```
>>
>> Thanks so much!
>>
>> --
>> Jake Vossen
>> Colorado School of Mines, Class of 2022
>> B.S. Computer Science
>> PGP: 08CD 67DA FE3A 0AE7 B946 6AC3 B812 7052 D9E3 817B
>> https://jake.vossen.dev
>>
>>
>> _______________________________________________
>> Beginners mailing list
>> [email protected]
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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Message: 2
Date: Wed, 15 Jan 2020 16:05:06 -0500
From: Julian Camilo Osorio <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Code review request?
Message-ID:
<CAHz-aL34soF4kSPZQD1iCZ+5JuHWoh5d16fPxccAGPVV-P+=j...@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"
For what it's worth, this is an equivalent one-liner:
canBalance xs = any ((== sum xs) . (*2)) (scanl (+) 0 xs)
On Wed, 15 Jan 2020 at 15:02, Akhra Gannon <[email protected]> wrote:
>
> Also worth noting that Ut's version can be expressed as a fold:
>
> canBalanceElem x acc@(y, z, p) = if p then acc else let y'=y+x; z'=z-x in
> (y', z', y'==z')
> canBalanceFold xs = (\(_, _, p) -> p) $ foldr canBalanceElem (0, sum xs,
> False) xs
>
>
> On Wed, Jan 15, 2020 at 10:54 AM Ut Primum <[email protected]> wrote:
>>
>> Hi,
>> this is how I would have solved the exercise:
>>
>> canBalanceRec [] _ _ = False
>> canBalanceRec (x:xs) s1 s2 = s1+x==s2-x || canBalanceRec xs (s1+x) (s2-x)
>> canBalance xs = s==0 || canBalanceRec xs 0 s where s=sum xs
>>
>> Note that there is one difference: in this case
>> canBalance [-2,-2,4] = True
>> because I think I can split the list into [ ] and the rest (since the sum of
>> the empty list is 0 and the same is the sum of the elements of the lists).
>> Anyway this is a matter of how we interpret the text of the exercise (your
>> function would return False instead). Note that removing the "s==0 ||" makes
>> no difference.
>>
>> An advantage of my solution is that it is less expensive, since its
>> computational complexity is linear in the length of the list xs. Yours uses
>> sum and drop many times, and so is slower. Just to have an idea of the
>> difference (using ghci interpreter):
>>
>> > canBalance [1..10000]
>> False
>> (0.02 secs, 6,974,552 bytes)
>> > can_split_even [1..10000]
>> False
>> (5.60 secs, 11,395,843,384 bytes)
>>
>> Cheers,
>> Ut
>>
>> Il giorno mer 15 gen 2020 alle ore 18:27 Jake Vossen <[email protected]> ha
>> scritto:
>>>
>>> Hey everyone,
>>>
>>> Let me know if this is not the right place for this, but I am curious if
>>> someone could take a look at my code and maybe share some feedback / how
>>> a more experienced haskeller would approach this problem.
>>>
>>> New to Haskell, pretty experienced with imperative languages. I have
>>> solved the following problem in Haskell:
>>>
>>> > Given a non-empty array, return true if there is a place to split the
>>> > array so that the sum of the numbers on one side is equal to the sum
>>> > of the numbers on the other side.
>>>
>>> > canBalance([1, 1, 1, 2, 1]) -> true
>>> > canBalance([2, 1, 1, 2, 1]) -> false
>>> > canBalance([10, 10]) -> true
>>>
>>> Here is my code (my solution uses `can_split_even` not `canBalance`)
>>>
>>> ```
>>> can_split_even :: (Num a) => (Eq a) => [a] -> Bool
>>> can_split_even xs = True `elem` is_even_at_each_spot
>>> where
>>> is_even_at_each_spot :: [Bool]
>>> is_even_at_each_spot = map (is_split xs) [1 .. (length xs - 1)]
>>> where
>>> is_split :: (Num a) => (Eq a) => [a] -> Int -> Bool
>>> is_split xs index = sum (take index xs) == sum (drop index xs)
>>> ```
>>>
>>> Thanks so much!
>>>
>>> --
>>> Jake Vossen
>>> Colorado School of Mines, Class of 2022
>>> B.S. Computer Science
>>> PGP: 08CD 67DA FE3A 0AE7 B946 6AC3 B812 7052 D9E3 817B
>>> https://jake.vossen.dev
>>>
>>>
>>> _______________________________________________
>>> Beginners mailing list
>>> [email protected]
>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
>> _______________________________________________
>> Beginners mailing list
>> [email protected]
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
------------------------------
Message: 3
Date: Thu, 16 Jan 2020 10:15:32 +0000
From: Leonhard Applis <[email protected]>
To: "[email protected]" <[email protected]>
Subject: [Haskell-beginners] Parallel Processing in Libraries?
Message-ID:
<2MKFj_uwsGLJVa39UEnu8rSYWGYLs2thwMKEytWB6FyyH82uI6dR1qCai3NNOpLC3wJiJ_GHBMkAfyY6WYhRwDqsmleDInE7R7KSELQqPQc=@protonmail.com>
Content-Type: text/plain; charset="utf-8"
Hi,
I'm starting to dip into Parallel Processing with Haskell while reading
"Parallel and Concurrent Programming in Haskell".
All the Examples in the Book construct a program which is doing all the work,
so with all files in the same program which has a main method.
I'd like to have a library which utilized parallel programming (mostly for
map-reduce tasks).
Is this possible?
My first approach of putting the par-code in my library and running the program
threaded does not seem to use multiple cores.
Also I have not seen any parallel programming in "popular" libraries (such as
QuickCheck) which makes me think that I'm on the wrong path.
To summarize my goal:
I want to build a computation-intensive library, which utilizes multiple cores
when used from an executable.
Thank you
Leonhard
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