Eric's Beijing Diary

Today, in the PL/SQL class, I was explaining functions, and how they differ from procedures. Without boring you with the details, a function is a specific type of procedure that always returns a value. I made the statement, "All functions are procedures, but all procedures are not functions."

One of my students corrected me,

"Not all procedures are functions."

He was right, of course. But so was I. If we say, "All that glitters is not gold," we do not mean by this that if something glitters, it can't possibly be gold. But the statement could be taken to mean that if we are not careful how we say it. And in writing, it can be hard to express the distinction. If we say instead, "Not all that glitters is gold," this removes the ambivalence, but it doesn't sound as good, you know what I mean?