Subject: RE: About Constructions rules From: "Didier PH Martin" <martind@xxxxxxxxxxxxx> Date: Sun, 11 Jul 1999 09:18:20 -0400 |
Hi Matthias, Matthias said: I wondered about that myself sometime ago. And no, query is not implemented. Its the only missing construct-expression. It may have been left out because this simplifies certain things. Eg, (current-node) will always be an element node unless you use query. The style-query-expression can be any expression returning a node-list, eg something like (q-element 'footnote (current-node)) returning all footnote elements within the current node. Note that (current-node) returns the root of the grove withing the style-query-expression. Didier says: You are right Matthias, I discovered after digging in the sources that it is not implemented. I guess your inference about why it is not implemented is right because we may end up with any kind of node-list as the result of a query. In may document talking about construction rules (ref: http://www.netfolder.com/DSSSL/MarkupRule.htm ) I used as an example the sgmal-parse as a query epxression. In this case the node returned is a sml-document type of node. So, the query construct adds more complexity by forcing us to process any kind of nodes. However this is a quite powerful construction rule. For instance, the following query construction rule, would include a sgml-document into a style sheet (this is an example extracted from the document referred previously) (query (sgml-parse ("<url>http://www.netfolder.com/doc.sgml")) (process-children) ) This is an easy way to include an external document to be processed into a style-sheet. I just scratched the surface of this construction rule power. An other usage I discovered by playing with it on paper is that you can do a specific query get back a node list and start locally to do some processing on this node list. This way, we have the concept of local procedure where you obtain a node-list and do some processing on it with node-list constructs. Yes indeed a very powerful construct with not much equivalent in other languages (does it? if yes, I would be interested to listen how other languages implement the same feature). PS: for those who want to renew their knowledge or just explore more about DSSSL, read the document talking about the constrcution rules and give me some feedback. ref: http://www.netfolder.com/DSSSL/MarkupRule.htm regards Didier PH Martin mailto:martind@xxxxxxxxxxxxx http://www.netfolder.com DSSSList info and archive: http://www.mulberrytech.com/dsssl/dssslist
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