Your critique about C values that can be made invalid (through lack of proper initialization or erroneous cast) are of course valid but sounds quite rhetorical, since in practice, in my experience, this does not cause many bugs (yet I'm sure you could site several examples of such bugs). What's of more practical importance to me is that when you change a data structure somewhere you can be confident that the compiler will spot every other places where your changes require other changes. You have not this safety with Scheme, and this is much more problematic ; again, in my experience. You have to run your code with all possible inputs in order to make certain that you did not forget to propagate your changes somewhere. This happened to me again two weeks ago when I decided that my small guile-agentx library should use bytevectors instead of strings to read/write from the socket. This small change had many other small impacts but I was alone to find them, had to run the code in many different situation to test many path before I gained enough confidence that I didn't forgot some string operation somewhere - yet this is a very small library!
Of course, I'm a beginner in Scheme so that might explain why my brain lacks the necessary equipment to typecheck myself ; while my first hello.c was written more than 20 years ago so maybe that's why I find C quite safe in practice. So, all in all, who knows? But I for sure would like to see type annotations added in guile some day :-)
