Uses of reentrant code?

Question

What are examples of types of applications or methods that should be reentrant? Or is it something that you should generally strive for?

Also, is it generally a given in (pure) functional programming that your code will be reentrant?

Answer 1

If your code has no side-effects whatsoever (which happens if it's 'purely functional'), it's re-entrant and thread-safe.

In UI development you encounter reentrancy issues. You get one UI event and start a chain of events that may cause the same event to fire before your first handler was done.