[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: XML design of ((a and b) or c)
On 12/15/06, Rick Marshall <rjm@z...> wrote: > Hi Ken > > The point here is quite subtle and VERY important. > > Let's just take "a AND b" or "a & b" to reduce the overloading of the > word and. > > Now if a and b are atomic and & is commutative the the order of > evaluation is unimportant and optimisers can play around to suit themselves. > > However, if a or b are not atomic and the calculation of either has side > effects then "a & b" is no longer commutative and optimisers cannot stop > the calculation on detection of a or b being false. > > Unless of course we agree to use slightly different mathematics: "a & b" > is not commutative; it is evaluated left to right; and evaluation stops > if a is false. This can then be extended to "a & b & c ...". > > Now the "a & b" of computer languages is fundamentally different to the > "a & b" of mathematics although they degenerate to the same thing if a > and b are atomic. > Just to be sure, & is different from && on C. & is the and operation betwen bits, the result is a integer && is the and operation betwen booleans, the result is a boolean 0x0F & 0xF0 result to 0 0x0F && 0xF0 result to true You will not use & for shortcuts, but &&.
[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] |
PURCHASE STYLUS STUDIO ONLINE TODAY!Purchasing Stylus Studio from our online shop is Easy, Secure and Value Priced! Download The World's Best XML IDE!Accelerate XML development with our award-winning XML IDE - Download a free trial today! Subscribe in XML format
|