I trying to learn a bit about data parallel haskell, and started from the wiki page here: http://www.haskell.org/haskellwiki/GHC/Data_Parallel_Haskell. Two questions: The examples express the dot product as: dotp_double xs ys = sumP [:x * http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:. y | x <- xs | y <- ys:] Unless I'm missing something, shouldn't this actually be: dotp_double xs ys = sumP [:x * http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:. y | x <- xs, y <- ys:] Second, when I run Main with the prescribed 10000 element array, everything seems to work quite nicely. The task takes about 2 seconds on my 4 processor x86_64, and threadscope shows all processors nicely utilized. However, when bumping this to 100000 elements, rather than taking 10x longer as I expected, the process never terminates. During one run I even lost control of my machine and needed to do a hard reset. Are there known limits to the array sizes that can be handled with dph, or can someone suggest what might be going wrong here? Thanks, Warren