Yes, that's true. I thought about mentioning that in my comment, but it seemed like a bit of a digression and it was already getting a bit wordy. Anyways, the

Yes, that's true. I thought about mentioning that in my comment, but it seemed like a bit of a digression and it was already getting a bit wordy. Anyways, the problem is that you might open a file, read it into a string, close the file, and then pass the string into some pure function. The problem is that the file was closed before it was lazily read, and so the string contents don't get populated correctly; you get the empty string instead, or whatever was lazily read before the file was closed. That was a design oversight from the early days. If you know about it, it's pretty easy to work around it in simple applications. There are some more modern libraries for doing file IO in a safer way, but I haven't used them and don't really know what the details are.