Subject: Re: Regular expression functions (Was: Re: [xsl] comments on December F&O draft) From: Jeni Tennison <jeni@xxxxxxxxxxxxxxxx> Date: Fri, 11 Jan 2002 13:31:37 +0000 |
Hi Mike, >> I suspect that the introduction of user-defined functions in XSLT >> will lead to more functions that do this [construct and return >> trees], but don't know whether people would feel it was acceptable >> for a built-in function. > > It's messy because of the problem that nodes have identity. You have > to define whether two calls of the same function return the same > tree or different trees. You mean, assuming that current-match() returned the node tree described in the mail, if I did: current-match()/mantissa == current-match()/mantissa would the result be true or false? Or if I did: match($string1, $regexp1) == match($string2, $regexp2) would the result be true or false? I think that in both cases returning different trees would be more consistent, since user-defined functions won't have the luxury of being able to reuse trees. > I guess one could say that it's explicitly implementation-defined, > and no-one would worry too much about it. But it's also something > you want to avoid if at all possible because constructing new trees > is always expensive. Is that because constructing *nodes* is expensive or is it the *links* between the nodes within a tree that makes things problematic? If the latter, then perhaps documentless nodes are a blessing ;) If the former, then it's a good argument for nested sequences, so you don't have to create nodes to provide structure. For example, given the problems that I described about processing x,y coordinates as pairs, there's a strong temptation to create pairs of coordinates as 'coordinate' elements with 'x' and 'y' attributes, rather than a simple sequence of integers. If sequences could be nested, I wouldn't feel that temptation. Cheers, Jeni --- Jeni Tennison http://www.jenitennison.com/ XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list
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