[scott_s]

This is why I say the C preprocessor can act as Turing-complete, because the expression and machinery, while separate, is both in the language itself.

Unfortunately, "can act as Turing-complete" is not a well defined concept. It is clearly not the same thing, and the distinction is important. Consider, as pointed out elsewhere in this thread, that we can always solve the halting problem for a C preprocessor program. We're in danger of violent agreement, though: I think we agree on the main points, just perhaps not on their relevance.

Since we've gone this far down the rabbit hole, I'd like to point out that C++ templates are Turing complete: http://netvor.sk/~umage/docs/3rdparty/C++%20Templates%20are%...