Hi Luca if you don't use (data parallel) list comprehensions you shouldn't need the {-# LANGUAGE ParallelListComp #-} annotation. Here's and example from the DPH page that uses them: dotp_double :: [:Double:] -> [:Double:] -> Double dotp_double xs ys = sumP [:x * y | x <- xs | y <- ys:] http://www.haskell.org/haskellwiki/GHC/Data_Parallel_Haskell If you are just using the DPH functionals mapP, zipP etc. {-# LANGUAGE PArr #-} should be all you need. GHC will need this extension to handle the [: :] type notation. I don't know about your second question, from the DPH page it looks like you need -threaded for multicore, but you can still run DPH code on single core (if you don't supply -threaded and link to the right library), see 1.5.6 Parallel execution. Best wishes Stephen