[Haskell-cafe] Don't “accidentallyparallelize”

Hi all, In "DEFUN 2009: Multicore Programming in Haskell Now!" (http://donsbot.wordpress.com/2009/09/05/defun-2009-multicore-programming-in-...), slide 30 I see: Don't “accidentally parallelize”: – f `par` f + e and that the correct way of achieving parallelism is: – f `par` e `pseq` f + e Actually I don't understand the difference between these two forms. Could any brave soul explain it to me, please? As a bonus question: what is the difference between `seq` and `pseq`? -- Gracjan