{"id":388,"date":"2008-11-28T22:47:47","date_gmt":"2008-11-29T05:47:47","guid":{"rendered":"https:\/\/dubinko.info\/blog\/?p=388"},"modified":"2008-11-28T22:47:47","modified_gmt":"2008-11-29T05:47:47","slug":"fun-with-xdmpvalue","status":"publish","type":"post","link":"https:\/\/dubinko.info\/blog\/2008\/11\/fun-with-xdmpvalue\/","title":{"rendered":"Fun with xdmp:value()"},"content":{"rendered":"

Lately I’ve been playing with some more advanced XQuery. One thing nearly every XQuery engine supports is some kind of eval()<\/code> function. MarkLogic has several, but my favorite<\/a> is xdmp:eval. It’s lightweight because it reuses the entire calling context, so for instance you can write let $v := 5 return xdmp:value(\"$v\")<\/code>. Not too useful, but if the expression passed in comes from a variable, it gets interesting.<\/p>\n

Now, quite a few standards based on XPath depend on the context node being set to some particular node. This turns out to be easy too, using the path operator: $context\/xdmp:value($expr)<\/code>. According to the definition of the XPath path operator, the expression to the right is evaluated with the results of the expression on the left setting the context node.<\/p>\n

OK, how about setting the context size and position? More difficult, but one could use a sequence on the left-hand side of the path operator, with the desired $context<\/code> node in somewhere in the middle. Then last()<\/code> will return the length of the sequence, and position()<\/code> will return, well, the position of $context<\/code> in the sequence. But it’s kind of hacky to manufacture a bunch of temporary nodes, only to throw them away in the next step of the path.<\/p>\n

I’m curious if anyone else has done something similar. Comments? -m<\/p>\n","protected":false},"excerpt":{"rendered":"

Lately I’ve been playing with some more advanced XQuery. One thing nearly every XQuery engine supports is some kind of eval() function. MarkLogic has several, but my favorite is xdmp:eval. It’s lightweight because it reuses the entire calling context, so for instance you can write let $v := 5 return xdmp:value(“$v”). Not too useful, but…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[27,113,9,124],"tags":[525],"class_list":["post-388","post","type-post","status-publish","format-standard","hentry","category-languages","category-mark-logic","category-standards","category-xquery-standards","tag-marklogic-eval-xquery-higherorder-context-xpath-sequence"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t