On 1/4/06, Luke Palmer <[EMAIL PROTECTED]> wrote:
> Of course, this was introduced for a reason:
>
> sub min($x,$y) {
> $x <= $y ?? $x !! $y
> }
> sub min2($x, $y) {
> if $x <= $y { return $x }
> if $x > $y { return $y }
> }
>
> In the presence of junctions, these two functions are not equivalent.
> In fact, it is possible that both or neither of the conditionals
> succeed in min2(), meaning you could change the order of the if
> statements and it would change the behavior. This is wacky stuff, so
> we said that you have to be aware that you're using a junction for
> "safety".
>
> But now I'm convinced, but I've failed to convince anyone else, that
> the behavior's being wacky doesn't mean that it should be declared,
> but that the behavior is just plain wrong. I figure that if something
> says it's totally ordered (which junctions do simply by being allowed
> arguments to the <= function), both of these functions should always
> be the same. The fact is that junctions are not totally ordered, and
> they shouldn't pretend that they are.
To me, this implies that junctions don't have a complete definition.
Either they're ordered or they're not. Either I can put them in a <=
expression and it makes sense or I can't. If it makes sense, then that
implies that if $x <= $y is true, then $x > $y is false. Otherwise,
the definitions of <= and > have been violated.
And, if I can't put them in a <=, then Perl should complain very
loudly, just as if I put something else that shouldn't be put into <=,
like a Person object. If I call min() or min2() with a Person object
and an array, I should expect loud complaints from the runtime. If a
junction cannot behave itself in a numeric comparison, then similar
complaints should be made.
Rob
