What are some more obscure control flow structures? It's easy to think that eg conditionals, loops, goto, function calls are the only ones that exist. But there is also stuff like jump tables and co-routines for instance.
But you have to read it slowly.
Now, off to study!
Thanks, btw.
Highly recommended.
http://rubydoc.info/stdlib/core/1.9.3/Kernel:callcc
Thus you can implement pretty much anything you want in ruby, including COME FROM.
They're what lies beyond exceptions: exceptions will unwind the stack looking for a handler (`catch` or the likes), and when found will execute that handler in its (the handler's) context (scope).
Conditions walk the stack instead of unwinding it, and execute the handler in their own context. This gives the handler the possibility of logging an error and bailing out, of course, but also of fixing the local data and resuming running the code[0], as if nothing had happened. A condition system essentially allows callees to reach into callers and ask them what to do, without having to lose any state or data.
This also gives more power to tools: without any specific instrumentation, a Smalltalk environment or a Common Lisp IDE can drop you at the error site (where the condition was signaled) without needing more than registering a condition handler when starting your code (if conditions are already handled by a condition handler in your stack, this default behavior won't happen until your handlers let the condition propagate further).
[0] Actual flexibility depends on the runtime, I'm not completely up to snuff with everything, I know in Common Lisp there's a concept of "restart": the one who signaled the condition or any of its callers can provide "restarts", which are essentially possible choices for resuming work. A log-parsing API could provide restarts to skip a corrupted or unreadable entry, to display a user prompt to ask him to "manually" parse the value or to provide the API with a value to use instead (could be a default, a placeholder, or a value obtained by calling the older log-parser you're trying to replace) (note: it's an inclusive or, the API provides all three and the developer using the API picks the one he wants depending on the situation). Or a dict's `get` method could signal on an invalid key and provide a restart making it return a default value of some sort.