[Haskell-beginners] Lions, Wolves and Goats

Francesco Ariis fa-ml at ariis.it
Sun Jun 8 06:33:56 UTC 2014

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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