Ouch! I see what you mean. And this is meant to be simplified? But the problem really is that if a user tries to use an identifier with an illegal syntax, how do they know? This is rather like those really annoying websites which ask you to choose a password, and then tell you that it's illegal without telling you why.
Simple: don't use too weird identifiers :-) I'll try to rephrase that part again. The point of mentioning this is to explain that '+', '-', '*', '/' are just procedures, not special syntax, and to address the question that I imagine this immediately raises in the mind of a reader used to more mainstream programming languages: "what, a procedure called '+', is that really valid"? There are also two conventions that are useful to know: - question mark at the end of a predicate (explained later in the tutorial), - exclamation mark at the end of a side-effecting procedure (I'm not showing any of these in this basic tutorial, so I didn't explain it). It's not really encouraged to get creative about special characters in your variable names. Just stick with the conventions. Cheers, Jean
