It's my code to do some recursive things, focus on function 'group'. ---- cow.hs year1 [y1,y2,y3,y4x] = y1 year2 [y1,y2,y3,y4x] = y2 year3 [y1,y2,y3,y4x] = y3 year4x [y1,y2,y3,y4x] = y4x cow_group_sum year = sum (group year) --look here-- group 1 = [1,0,0,0] group (year+1) = [(year4x (group year)), (year1 (group year)), (year2 (group year)), ((year4x (group year)) + (year3 (group year)))] main = print (cow_group_sum 50) ---- end Every time 'group' was called, the (group year) function was called 4 times . when call (group 30), it takes tens seconds to finish. I have tried 'ghc -O3', but it's still 'lazy' on this thing. Map-Reduce seems to be the answer to the question. But I want to make sure that ghc CAN or CANNOT do the Optimize for Dynamic Programming? ---------------- xingbo wu