Oh, nevermind. The problem was in other place not in that function. I'm sorry for this... Best Regards, Karol Samborski 2011/11/9 Karol Samborski :

I forgot to mention that this definition: saturation (_,edges,_) = length $ foldr (\ed ac -> colors!ed : ac) [] edges is working too.

I don't understand why the version with an 'if' is not working.

Best Regards, Karol Samborski

2011/11/9 Karol Samborski :

...

Hi,

With a function defined like this (colors is type of Array Int [Int] and edges is [Int]): saturation (_,edges,_) = foldr (\ed ac ->if null (colors!ed) then ac else ac+1) 0 edges I'm getting an infinite loop.

But when I remove the if statement like this: saturation (_,edges,_) = foldr (\ed ac -> ac+1) 0 edges everything's working.

How should I define my function with the if statement to not getting an infinite loop?

Best Regards, Karol Samborski