Parallelism and concurrency are certainly different. Don't think I'm saying otherwise. Our disagreement is that I'm saying parallelism is a subset/type of concu

Parallelism and concurrency are certainly different. Don't think I'm saying otherwise. Our disagreement is that I'm saying parallelism is a subset/type of concurrency and you are saying parallel execution can somehow not be concurrent execution. I still stand by my assertion that you misunderstood the quote from the Haskell wiki: "Rule of thumb: use Pure Parallelism if you can, Concurrency otherwise." as something that supports your claim that parallelism is not concurrency. From Wikipedia: "In computer science, concurrency is a property of systems in which several computations are executing simultaneously, and potentially interacting with each other. The computations may be executing on multiple cores in the same chip, preemptively time-shared threads on the same processor, or executed on physically separated processors." I find it hard to believe that parallel execution of multiple threads aren't "computations executing simultaneously" and therefor aren't concurrent. Do you have any more detail about why you (or Rob Pike) think that parallel execution is not also always concurrent execution?