I've been looking around on the web for reasons why decimal arithmetic should be added to ES. The most extensive page I could find was http://speleotrove.com/decimal/decifaq.html. If anyone know other good sources of information about decimal and its inclusion in ES please follow up.
The strongest argument seems to be financial: binary arithmetic is approximate in a way that makes it unsuitable for financial calculations. I buy this argument in general -- I would definitely want my bank to use some form of decimal arithmetic rather than binary -- but less so in the context of ES. A while ago we (the v8 team) asked around within google and were unable to find anyone who would want to do financial calculations client-side. Financial calculations are sensitive and keeping it on the server makes it possible to maintain consistency, accountability, testability and reproducibility. So while I'm all for decimal in languages that run server side it's much less relevant for a language that runs almost exclusively on the client. Another data point is that the one decimal library that exists for JS, a direct translation from Java's BigDecimal, hasn't been updated since 2000, during which time a number of bugs have been fixed in Java BigDecimal. If there had been a broad interest in using a JS decimal library I would expect there to be a well-maintained one around. I found a handful of blog posts supporting decimal from an accuracy standpoint -- essentially "0.1 + 0.2 should be equal to 0.3". The argument looks compelling but is somewhat misleading. All floating point arithmetic is approximate. K-bit decimal arithmetic trades smaller but conspicuous inaccuracies for greater but less conspicuous ones when compared with k-bit binary. In some contexts, financial again for instance, the accuracy argument makes sense but not as a general statement without qualification. Nonetheless, far as I can tell this is the source of a large portion of the requests for supporting decimal. Furthermore, decimal itself is counter-intuitive in a number of ways: the difference between 1e2 and 100, for instance, is counter-intuitive in many contexts. I know the most obvious differences have been removed from the ES proposal; I'm not sure if there are less obvious differences left (like with +/-0). Another problem is that the standard is closed: I can't even read it without paying for it. Granted, that also holds for the specification of double but with double there is universal native support, we don't have to maintain an implementation ourselves. That's not the case for decimal. We as implementers of the language would have to potentially create or at least maintain an implementation of a closed standard. Finally, the usefulness of decimal either a native implementation or a library would have to be weighed against the increase in the size of the implementation. The fact that JS is becoming increasingly popular on limited devices speaks against adding a large decimal library. -- Christian _______________________________________________ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
