I'd add that it also works because nobody ever says "foo-bar". What "foo" and "bar" actually are, plus context, lets the (human) reader know what's going on.

I'd add that it also works because nobody ever says "foo-bar". What "foo" and "bar" actually are, plus context, lets the (human) reader know what's going on. Even if I don't know what programming language you're talking about, if I see x2-x1 or margin-75 I know you probably mean subtraction, and if I see last-name or message-id you probably mean a single identifier. I've seen plenty of Lisp code that says things like x2-x1 in docstrings (because it is shorter) and I've never found it to be confusing.