Yes, that's exactly what I was pointing at. If you keep "statement" and "expression" separate, it's obvious that "EXPR1 while EXPR2;" is a statement, not an expression, and cannot further be modified, and that "EXPR1 or EXPR2" is still an expression and can be used in a larger expression.

If you start blurring the concept of "statement" and "expression", you'll be surprised because you start having to use terms like "sometimes" and "mostly". But the rules are actually very obvious once you separate them cleanly.

-- Randal L. Schwartz, Perl hacker