Re: Question about parser implementation details

On 2012-04-01, Florian Anderiasch <ml@anderiasch.de> wrote: > Hey there, > due to the widespread acceptance of binary number format (0b1010101) and > the growing demand for backwards compatibility I've started to work on > support for Roman Numerals (I, II, III, ...) > > As you might know, this format cannot be strictly parsed from left to > right or right to left, as several number values need a look-ahead > before being able to compute them (like IV), so my naive first > implementation splits the string into tokens (like in 1990 = MCMXC => > M,CM,XC => 1000,900,90) then simplifying those 3 on their own, then > adding the results, but I'm not sure this could kill performance if > calculated inside zend_language_scanner.l. Thanks for the work on it. I really appreciated and would love to see roman numberes finally get implemented. I think a fair asusmption is that there is a certain ordering. First add numbers unless you encouter a higher or lower number: (1) in case current number == previous number, add it to your temp buffer (2) in case current number < previous number, add it to your temp buffer (3) in case current number > previous number, substract it from temp buffer Obviously you need to check if hte number is valid too: IIVM is obviously wrong But i think this is a good start.