[Haskell-beginners] Lions, Wolves and Goats

[Tim Perry]

Oops, I forgot the gist location.
https://gist.github.com/anonymous/99bc650c41e07364764c


I tried a set-based solution and it can process ~1600 items in 25 seconds
on this i7. Seems really slow compared to the times posted here:
http://unriskinsight.blogspot.co.at/2014/06/fast-functional-goats-lions-and-wolves.html

I'm curious if anyone spots any major flaw. If not, I'll profile it tonight
-- I can't afford to spend more time on this at work



On Mon, Jun 16, 2014 at 4:15 PM, Tim Perry <tim.v2.0 at gmail.com> wrote:

> I tried a set-based solution and it can process ~1600 items in 25 seconds
> on this i7. Seems really slow compared to the times posted here:
>
> http://unriskinsight.blogspot.co.at/2014/06/fast-functional-goats-lions-and-wolves.html
>
> I'm curious if anyone spots any major flaw. If not, I'll profile it
> tonight -- I can't afford to spend more time on this at work
>
> Tim
>
>
>
> On Fri, Jun 13, 2014 at 8:54 AM, Elric <elric at kiosa.org> wrote:
>
>>  Thank You Bob,
>>
>> I learnt quite a bit from your solution. I have been restricting myself
>> to Lists so far. I think I will have to start exploring other data
>> structures like Sets in Haskell as well. :)
>>
>> Thank You,
>> Elric
>>
>>
>> On 06/08/2014 03:41 PM, Bob Ippolito wrote:
>>
>> Here's another approach that more closely models what's going on in the
>> C++ version. I defined an ordNub rather than using nub as nub is O(n^2) as
>> it only requires Eq.
>>
>>  https://gist.github.com/etrepum/5bfedc8bbe576f89fe09
>>
>>  import qualified Data.Set as S
>> import Data.List (partition)
>> import System.Environment (getArgs)
>>
>>  data LWG = LWG { _lion, _wolf, _goat :: {-# UNPACK #-} !Int }
>>      deriving (Show, Ord, Eq)
>>
>>  lionEatGoat, lionEatWolf, wolfEatGoat :: LWG -> LWG
>> lionEatGoat (LWG l w g) = LWG (l - 1) (w + 1) (g - 1)
>> lionEatWolf (LWG l w g) = LWG (l - 1) (w - 1) (g + 1)
>> wolfEatGoat (LWG l w g) = LWG (l + 1) (w - 1) (g - 1)
>>
>>  stableState :: LWG -> Bool
>> stableState (LWG l w g) = length (filter (==0) [l, w, g]) >= 2
>>
>>  validState :: LWG -> Bool
>> validState (LWG l w g) = all (>=0) [l, w, g]
>>
>>  possibleMeals :: LWG -> [LWG]
>> possibleMeals state =
>>   filter validState .
>>   map ($ state) $ [lionEatGoat, lionEatWolf, wolfEatGoat]
>>
>>  ordNub :: Ord a => [a] -> [a]
>> ordNub = S.toList . S.fromList
>>
>>  endStates :: [LWG] -> [LWG]
>> endStates states
>>   | not (null stable)   = stable
>>   | not (null unstable) = endStates (concatMap possibleMeals unstable)
>>   | otherwise           = []
>>   where (stable, unstable) = partition stableState (ordNub states)
>>
>> main :: IO ()
>> main = do
>>   [l, w, g] <- map read `fmap` getArgs
>>   mapM_ print . endStates $ [LWG l w g]
>>
>>
>>
>> On Sat, Jun 7, 2014 at 11:33 PM, Francesco Ariis <fa-ml at ariis.it> wrote:
>>
>>> On Sat, Jun 07, 2014 at 08:04:09PM -0400, Elric wrote:
>>> > Hi,
>>> >
>>> > I came across this article:
>>> http://unriskinsight.blogspot.co.at/2014/06/fast-functional-goats-lions-and-wolves.html
>>> > a couple of days ago. This compares performance of solving a problem
>>> > (which I will get to) using the functional constructs alone in
>>> > languages like C++11 and Java 8.
>>> > Since, Haskell is my first foray into FP, I thought I should try
>>> > solving this in Haskell.
>>> >
>>>
>>>  Hello Elric,
>>>     I gave a go at the problem, managed to get a result (23).
>>> I attach the .hs file (not my best Haskell, but hopefully clear enough).
>>>
>>> The crucial point in my solution lies in this lines:
>>>
>>>     carnage :: [Forest] -> [Forest]
>>>     let wodup = nub aa in
>>>     -- etc. etc.
>>>
>>> Which means after every iteration I call |nub| on my list of possible
>>> states; nub is a function from |Data.List| and removes duplicate
>>> elements from a list.
>>>
>>> If I omit that nub call, the program doesn't reach a solution (as it
>>> is computationally quite inefficient). I think that's the problem
>>> with your versions.
>>>
>>> Let me know if this helps
>>>
>>>
>>>
>>>
>>>
>>>
>>>
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>>> Beginners at haskell.org
>>> http://www.haskell.org/mailman/listinfo/beginners
>>>
>>>
>>
>>
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