I think I agree with most of that. I'm definitely a big fan of CSP, and some of its ideological successors. To this day I think that Occam is one of the most

I think I agree with most of that. I'm definitely a big fan of CSP, and some of its ideological successors. To this day I think that Occam is one of the most ingeniously elegant languages ever invented. I also think that making a distinction between concurrency and sharing is rather artificial. Embarrassingly parallel problems aside (where the concurrency is really better characterised as co-habitation of a computing resource), it's still pretty easy to get both shared-memory and channel-based message-passing wrong in concurrent situations. I agree that the presence of shared-memory makes it worse, and while my experiences using things like CML without using mutable storage have been much more positive than say... Java concurrency primitives, I think it's still "hard" in that it requires considerably more intellectual effort than writing non-concurrent programs of similar scope and size.