Hello, In Control.Parallel.Strategies, parList is defined as parList strat [] = () parList strat (x:xs) = strat x `par` (parList strat xs) with parMap strat f xs = map f xs `using` parList strat. I have recently found that if I define forceParMap strat f xs = map f xs `using` forceParList strat where forceParList strat = foldl (\done -> (done>||) . strat) () then to date, forceParList via forceParMap gives faster results than parList via parMap. For example, in one experiment, parMap with parList run at 0.81 the time of the serial solution whereas forceParMap with forceParList run at 0.58 the time of the serial solution. This is to say, forceParList completed in 0.72 the time of parList. So, 1. Why is forceParList faster than parList? 2. Is this generic to the ghc runtime model or a particularity of the ghc implementation? Thanks in advance for the clarification, - Marcus