RE: Who said that?

["Anton van Straaten" <address@hidden>]

> > there's a quote whose source and exact wording I can't recall.
> > The sentiment goes something like: "When you read about it,
> > [blank]; when you can teach it, [another blank]; when you
> > can program it, you understand."  Does anyone know what this
> > quote is?
>
> If we're thinking of the same quote, then Alan Perlis said that,
> and it goes like:
>
> "You think you know when you learn, are more sure when you can
> write, even more when you can teach, but certain when you can
> program."

In direct contrast to the claims in these quotes, I noticed this quote at
the end of Part I of Pierce's "Types and Programming Languages":

"Just because you've implemented something doesn't mean you understand it"
   -- Brian Cantwell Smith

  (...who, btw, has some interesting papers at
  http://www.ageofsig.org/people/bcsmith/papers/ )


Anton