Code Notelets

Learning to use unwind-protect in Lisp typically crops up very early on when you're first learning the language. In fact, anything to do with I/O is going to be something you'll need to know early on. Yet unfortunately, I find that unwind-protect is not explained sufficiently well for a beginner to understand not just how to use it correctly, but why and when . Grappling with this myself, I found that hands-down the best explanation came from this YouTube video from Baggers: Luckily, in the case of file handlers, LISP already assumes you'll want to open a file with unwind-protect, so it provides the with-open-file macro for this exact purpose. It closes the file handler for you with a built-in unwind-protect. This is an advantage over manually opening and closing your file handlers, because if your program opens the file but never gets to the part with the close command (for example due to a run-time error in between those stages), the built-in unwind-protect make