Subject: Re: [xsl] Re: How to express this in XPath: "when condition doaction" where condition cannot be evaluated until data arrives later From: "Graydon graydon@xxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> Date: Tue, 20 Dec 2022 14:29:52 -0000 |
Hi Roger --- On Tue, Dec 20, 2022 at 02:20:26PM -0000, Roger L Costello costello@xxxxxxxxx scripsit: > I am implementing an application that processes a sequence of XPath > expressions. Some XPath expressions can be evaluated immediately > because all the data is present in full. However, in some cases not > all the data is present in full. In my car example, the decision to > output the license plate number or null cannot be made until the > relevant police report arrives, which may occur at some time in the > future. So evaluating the XPath for the car example must pause until > the police report arrives. Or it could fail and be re-run periodically? It makes sense that you want to wait on an external event before returning a result. In a declarative expresion language that avoids side-effects, you're going to have to fight with it a lot if you try to implement that in a literal way. What happens if the police report never arrives? -- Graydon Saunders | graydonish@xxxxxxxxx ^fs oferiode, pisses swa mfg. -- Deor ("That passed, so may this.")
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