On Thu, Oct 1, 2015, at 16:07, MRAB wrote:
If a is falsy, it short-circuits "a and b".
The parenthesised expression returns a falsy result.
That falsy result then short-circuits "(a and b) and c".
It happens to show the same behaviour as "a and b and c" and can be optimised to that.
Er... that's what a and b and c *is*. The 'and' operator is a left-associative binary operator. ((a and b) and c) is literally the same AST as (a and b and c). Being optimized to "short-circuit the whole thing" is an optimization for both of them. The naive way you describe of evaluating each one in turn is also the same for both of them. They are in fact both being optimized to (a and (b and c)) [rather, to the same byte code that a 'naive' implementation would still generate for that expression].