The only person who seems to be getting “pissy” is you.
What is the point of making a comment like “if you don’t like it, leave?”. People who say this seem to think they’re some pithy genius but it’s not a comment that advances the conversation at all.
“Hey I have some feedback ...”
“I don’t accept feedback. Take it or leave it”
“Ok”
That’s not really what HN is meant for.
Does the conversation really need to be advanced? The author has chosen to not include answers and gave an extremely valid reason for choosing not to and HN'ers are, indeed, getting pissy saying the author should do the "right thing" and provide the answers.
No. Just no. The "right thing" is to accept that the author is choosing not to and move on if you need answers. The author doesn't owe anyone answers.
The discussion is about whether his decision may be criticized. Which it absolutely can be.
Again, saying, “if you don’t like it, leave” is not the genius rejoinder you seem to think it is. It doesn’t add anything to the discussion.
I could flip this back at you and say “if you don’t like this discussion, leave”. I’m not doing that because I choose to engage in a good faith discourse.
Exercises with no solutions are very hard for people learning away from traditional academia - I haven't read this book so I don't know what they're like, but in a physics books it's often common to add questions that take fairly deep conceptual understanding which if you don't click with the book means you're totally out of action until you find somewhere else to learn from.