Re: Fusion Laws?

On Thu, Mar 31, 2016 at 1:45 PM, Michael Haufe <
[email protected]> wrote:

> On Thursday, March 31, 2016 at 1:22:14 PM UTC-5, Jason Orendorff wrote:
> > The specification technique isn't the problem. It's the semantics being
> > specified. They are the semantics of a dynamic language. Reasoning about
> > such code is an exercise in hand-waving.
>
> Perhaps I'm misreading your statement here, but are you saying that the
> current spec is hand-waving the runtime semantics of the language, or are
> you instead saying that one can't formalize the semantics of a dynamic
> language?
>

No and no. (The current spec is very detailed. The semantics of JS could
certainly be formalized; I'm not sure you'd learn anything new though.)

I'm saying that the way JS programmers reason about their code---when we
reason about it at all---hand-waves away all the complicating factors that
JS engines are forced to treat seriously. We take for granted that many
possible things that *could* theoretically happen, won't happen. We assume
(rather than prove or propagate) a bunch of antecedents like "well, x and y
are both gonna be numbers here, and neither one can be NaN, and this
addition won't overflow, and this object won't be a proxy..."

JS implementations (and the spec itself) don't have that luxury.

-j