Hello Haskellers, I supervise a student who uses Haskell for simulating neural nets. A lot of computation goes on there and the program cannot handle as many iterations as we would like. We have improved performance by a factor of more than ten by putting strictness annotations in all data types. But the problem is that there are lists within these data structures and they are not strict. By using a trick I have now found that making the whole program state strict the program gets a much better looking heap profile. The trick I use is by writing a function hyperseq and then applying it before the next iterations begins: hyperseq x y = if x==x then y else error "this is very unlikely" This is very expensive and I chose to apply the function only once every 100 iterations. This gives reasonable performance. Two questions remain: 1) Is there a more efficient definition of hyperseq that does not traverse the data structure twice? The "show" function traverses the structure once but I found it to be much slower. 2) In this application the uses of lazy evaluation are rare and easily eliminated (zip xs [1..] and so on); is there some hidden GHC option that evaluates everything strictly? I realise that this would invalidate optimisations relying on certain laws but I just wonder how difficult this would be. Somebody must have given this a thought at one point. Cheers, Arjan