Sticking a Hand Through Time: Adventures on the call stack

That depends entirely on the calling convention - potentially you can take two words down from the first argument, but that is no guarantee, and would not suffice for the didactic goals this article attempts to accomplish.

I've always wondered: if I implement Common Lisp in C or Fortran, what does that say about Common Lisp?

There is no special call stack manipulation in the CL condition system. It's built on top of dynamic scoping and normal catch/throw unwinds; see http://www.pipeline.com/~hbaker1/MetaCircular.html for block/return-from on top of catch/throw.

It is equivalent to:

  if (x == 1 || x == 2 || x == 3 || x == 4)
    printf("What the fuck?");

My guess would be that it triggers a compiler error because of the missing braces {}. However, reading http://en.cppreference.com/w/c/language/switch and https://msdn.microsoft.com/en-us/library/66k51h7a.aspx, I am starting to wonder about that. Both pages claim that switch(expression) can be followed by any statement, not just compound ones.

That seems to make it legal C. It also would make

  switch(i) x += 1;

and possibly even

  switch(i) foo: x += 1;

valid (but nonsensical) C. Chances are that the standard contains special wording that prohibits the latter two, though. If not, this is useful to know for the obfuscated C contest (more so if you can jump to that label)