ES Decimal status

Brendan Eich brendan at mozilla.org
Wed Sep 24 09:33:53 PDT 2008


On Sep 24, 2008, at 9:18 AM, Sam Ruby wrote:

>> [over-top-citing trimmed]
>> The concern remains, though. Not due to power-of-five problems that
>> would lead to 0.09999999999999987 or the like, but from cases where a
>> number was spelled with extra trailing zeros (in external data,  
>> e.g. a
>> spreadsheet) but fits in an integer, or otherwise can be expressed
>> exactly using powers of two. The burden of proof here is on the
>> invariant breaker :-/.
>
> I fully appreciate the need for a high bar here.

Sure, so maybe that bar height is why people talk about "broken".  
It's a presumption of "guilt", alien to Anglo-Saxon jurisprudence.  
The Napoleonic ECMAScript code prevails here. Beware! :-P.


> The problem here is that there are two invariants.  === to a high  
> degree
> of accuracy today is an eq operator.  But people have argued  
> against 1.2
> !== 1.20, because of another invariant:
>
> a == b && typeof(a) === typeof(b) implies a === b
>
> We can't satisfy both.

I do not think === is eq -- it's hard to argue degree when kind is  
the issue, as others have pointed out. Any hashcode addition would  
want eq, or force people to invent it at tedious and ineffecient length.

Past posts here have mixed up cohort and -0 vs. 0, but we've been  
educated thanks to MFC. Really, === breaks down on NaN and the  
zeroes, and there's no way to rationalize it as eq. I noted how Guy  
Steele helped us get past one broken equality operator, in order to  
add === and !== in ES1, and we talked about eq then. It still looms  
in the future, Harmony or (some argue) 3.1.


>  My initial preference was that 1.2 !== 1.20, but
> as we are not aware of code that uses fractional indexes, but are  
> aware
> of code that does generic typeof and equality testing, I would think
> that the latter would have a higher weight.

Ignoring === as faux eq, the only issue here is d.toString() for  
decimal d: should it preserve scale and stringify trailing zeroes and  
funny exponents?

/be

>
>> /be
>
> - Sam Ruby
>
>
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