You don't usually need them to do IO and state, but they're useful for things like optional and error values. Otherwise, it is mostly pedagogical. Besides, wri

You don't usually need them to do IO and state, but they're useful for things like optional and error values. Otherwise, it is mostly pedagogical. Besides, writing things that exist in other languages is useful when you're writing other languages. If you were using C to write a new language with closures (for instance,) you're going to have to implement closures in C. That's a useful exercise, even if nobody is going to use such an inevitably clunky construct in C directly.