marklogic - XQuery concat not outputting document XML in expected way -

let $d := doc('foo.xml')  return concat('let $d := 

', $d) 

returns

let $d :=  bar 

i need return:

let $d :=  <foo>bar</foo> 

reading function signature fn:concat, there no reason expect output xml. http://www.w3.org/tr/xpath-functions/#func-concat

fn:concat(   $arg1 xs:anyatomictype?,   $arg2 xs:anyatomictype?,   ...) xs:string 

that is, takes variable number of atomic items , returns string. if pass xml node, attempt atomize , return string result. if haven't run atomization yet, try string(doc($uri)) see happens.

ignoring that, looks you're trying build xquery expression using string manipulation - perhaps use xdmp:eval? that's fine, don't pass in xml using xdmp:quote. correctness, performance, , security reasons, right tool job external variable.

xdmp:eval('   declare variable $input external ;   let $d := $input   return xdmp:describe($d)',   (xs:qname('input'), $d)) 

better yet, write string part separate xquery module , xdmp:invoke same external variable parameters.

why way? correctness, efficiency , security. if habit of blindly evaluating strings, setting problems. passing node reference more efficient quoting large node. when quote xml string may end xquery-significant characters, such {. have escape them (or switch using xdmp:unquote, makes less efficient). escaping error-prone. in sql classic way handle bind variable, , xquery external variable. bind variables in sql, external variables handle escaping. makes injection attacks more difficult.