Re: Lua workshop: call for backup presentations.

["Andy Stark" <AStark@...>]

Lua list <lua@bazar2.conectiva.com.br> on Thursday, August 24, 2006 at
11:00 +0000 wrote:
>Since bignums are part of Common Lisp they deserve to be on the  
>roadmap for Lua.  Don't see why we should be wedded to a radix 10  
>implementation though.

The main advantage of decimal arithmetic is that it behaves exactly like
paper arithmetic. If you do a sum like 0.99 + 0.01 you get exactly 1 as
the result instead of merely getting the result of adding the binary
approximations of 0.99 and 0.01. I think we would all save ourselves a few
bugs by adopting BCD, but it is of most value to non-professional
programmers who wouldn't easily understand why comparisons sometimes don't
work. (For "non-professionals", think about most users of VoodooPad,
Lightroom, games, etc). The ECMAScript 4 (ie, JavaScript 2.0) proposal
contains a recommendation to support decimal arithmetic, optionally as the
default numeric type:-

	http://developer.mozilla.org/es4/proposals/decimal.html

Brendan Eich gave a presentation about the future of JavaScript in May
2006 where he claims that arithmetic inaccuracies are the most duplicated
bug in the Mozilla project:-

(Go to page 38 at
	http://ajaxian.com/downloads/presentations/eich-ajax-experience-2006/
) 

Also, as has already been mentioned, some financial software is legally
required to use decimal arithmetic to minimise the chance of fraud. The
quirky but clever old language of Rexx has always used decimal arithmetic
as its only numeric type and Python has recently added a decimal module to
its standard library.

BCD can be converted to and from a decimal textual representation very
quickly and without error. This means that it is often actually faster
than binary for programs that do text processing but relatively little
arithmetic (think of, say, numeric attributes in an HTML-generating
script). Perhaps this might also slightly speed up the compilation of
source files written in Lua, but I'm not too sure about that.

I think BCD feels like a natural Lua thing and in cases where it's not
efficient enough it's easy to replace it with floats or integers. And it
will give you something to talk about at the round table ;-)

&.


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