Although, if you are writing a book to teach programming, you can't suddenly drop stuff like "evaluating expressions" on readers either. It might be meaningless to them.
For example. If they come from a 'toy' programming background where they just call functions that return values, set variables, jump to labels, and do some math... Even if they're experts at that task, the words "evaluating expressions" might likely have no meaning to them at all. You'll have to explain first with concepts they already understand.
In this case, it seems the writer might've come from such a background. (And assumed his contemporaries were in a similar mindset.) :)
For example. If they come from a 'toy' programming background where they just call functions that return values, set variables, jump to labels, and do some math... Even if they're experts at that task, the words "evaluating expressions" might likely have no meaning to them at all. You'll have to explain first with concepts they already understand.
In this case, it seems the writer might've come from such a background. (And assumed his contemporaries were in a similar mindset.) :)