On Sep 17, 2008, at 10:06 PM, Mark S. Miller wrote: > > >> 0/-0 != 0/0. Does it thus seem wrong that -0 === 0? >> >> Well, yes, actually it does seem wrong to me, but we all accept >> that particular wrongness. This is just more of the same. > > A lot more. > > Two wrongs don't make a right. > > One exception to the rule is better than two, or 2^53 or larger. > > "apart from somthing like significance" is a huge new set of > exceptions. A large enough set that we can no longer understand === > as approximating operational equivalence. If instead we understand > === to be asking whether two operands are cohorts, and we define > cohorts to be those numeric values that exactly represent a given > real number, then > 1) -0 vs 0 is no longer irregular > 2) We can explain why 1.5 === 1.5m === 1.5000m > 3) We can explain why 1.1 !== 1.1m.
I think it is a tenable position that 1.5m === 1.5000m based on the "cohort" concept, since performing the same operation on both will give answers that are in the same "cohort" equivalence class. But 1.5 / 10.0 != 1.5m / 10.0, and indeed, the answers would not even be in the same cohort. A notion of 'cohort' equivalence class based on correspondence in the abstract to the same real number but divorced from the actual semantics of the programming language strikes me as incoherent. I think such a notion of equivalence class only makes sense if performing identical operations on members of the same cohort gives answers which are in the same cohort. As a reductio ad absurdum, consider that we can place ECMAScript strings in one-to-one correspondence with arbitrary precision integers by considering them as base 2^16 numbers, but surely no one would argument that this implies "00" === 3145776L. That's because in defining a type, it is not just the set of represented values that matters for type equivalence, but also behavior of operations on that type. Regards, Maciej _______________________________________________ Es-discuss mailing list Es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
