Hello everybody! For testing purposes, I punched down a small program which... + puts 2^n elements into an unmutable vector (fromList); + generates a random index in the vector (using random-mersenne); + reads the value at the index i and at i+{-2,-1,1,2} and makes product of these values (making sure the indices stay within the boundary of the vector using `mod 2^n'); + makes a new vector with the product replacing the element at the index; + repeats the whole process 10^7 times starting from the random index. Now, after enforcing a minimum of strictness and profiling the program, I find that for some odd reason the program spends most of its time calculating the product of the read numbers! This is completely contrary to what I expected; namely, that it would spend most of the time either a) generating random numbers, b) reading the vector, or c) making a new vector. But it turns out, that reading the vector or indeed making the new one takes only a fraction of the actual time. I have attached the program and the profile to this email. Could it be that profiling assigns the Cost Centres to the wrong parts of the program? Did I overlook something crucial? Most likely the program could be implemented in a smarter way, but it's pretty close to what my actual program looks like and it shows similar behaviour. (My code, additionally, has a Boltzmann-weighed probability condition on whether the new value gets written to the vector or not.) I would be very happy for some input on this, because I am pretty new to Haskell and I don't really know how to do proper profiling. Cheers Janis (This being my first email to this mailing list, I hope I adhere to all rules of conduct out there; please tell me if I should have written this email differently or more concise.)