Functions

The XQuery language supports declaring functions and grouping them together in library modules. As your code grows more complex this helps keep it manageable. Here's the above query rewritten to use some local functions (which use the "local" namespace) to build the query piece-by-piece. Notice there's typing information for variables and return values. That's optional but usually a good idea. Each type accepts a modifier the same as in regular expressions: asterisk means 0 to n many, question mark means 0 or 1, plus means 1 to n many, and no modifier means exactly one.

declare function local:random-word()
as xs:string
{
  let $words := ("release", "thank you", "function")
  let $random := 1 + xdmp:random(2)
  return $words[$random]
};

declare function local:lists-query(
  $lists as xs:string*
) as cts:query
{
  cts:element-attribute-word-query(
    xs:QName("message"), xs:QName("list"), $lists
  )
};

declare function local:types-query(
  $types as xs:string*
) as cts:query
{
  cts:element-attribute-value-query(
    xs:QName("message"), xs:QName("type"), $types
  )
};

declare function local:word-query(
  $word as xs:string
) as cts:query
{
  cts:or-query((
    cts:element-attribute-word-query(
      xs:QName("message"), xs:QName("list"), $word, "unstemmed", 3
    ),
    cts:element-word-query(
      xs:QName("subject"), $word, "stemmed", 2
    ),
    cts:element-word-query(
      xs:QName("para"), $word, "stemmed", 1
    ),
    cts:element-word-query(
      xs:QName("quotepara"), $word, "stemmed", 0.5
    )
  ))
};

declare function local:get-query(
  $lists as xs:string*,
  $types as xs:string*,
  $word as xs:string*
) as cts:query
{
  cts:and-query((
    local:lists-query($lists),
    local:types-query($types),
    local:word-query($word)
  ))
};

let $lists := ("httpd", "firefox")
let $types := ("announcements", "general", "development")
let $word := local:random-word()
let $query := local:get-query($lists, $types, $word)
return
<ul>
{
for $m in cts:search(/message, $query)[1 to 100]
return <li>{ $m/headers/subject/string() }</li>
}
</ul>

To break functions into library modules you put them in a separate file and give them a special header. Here's file test-lib.xqy (which is already installed on the box for you):

module namespace test="http://try.marklogic.com/test";

declare default function namespace "http://www.w3.org/2005/xpath-functions";

declare function test:median(
  $values as xs:int*
) as xs:int
{
  let $sorted :=
    for $value in $values
    order by $value
    return $value
  let $midpoint := count($sorted) idiv 2
  return $sorted[$midpoint + 1]
};

And here's how you import the library and use it:

import module namespace test = "http://try.marklogic.com/test" at "/lib/test-lib.xqy";

let $values := (7,4,2,3,1,6,5)
return test:median($values)

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Functions