> bxcode:inline-variables($xqcode-uri) as xs:string
> @returns xquery code that is the source code from $xqcode-uri but with
> inlining "constant" variables and operations applied
>
> This could be used as a preprocessor.
> Is this something that could be created from the bits and pieces in the
> current BaseX Java code?

This reminds me of the discussion with Omar [1]: There is currently no
way to generate a correct string representation for compiled code. In
the GUI Info View, we output a string representation of the optimized
query. In simple cases, this string is a valid and equivalent to the
original query string, but it’s fairly easy to generate invalid
results.

If it’s an option for you to generate code in XQuery, something like
the following could be done:

_ bxcode.xqm _______

  module namespace bxcode = 'bxcode';
  declare function bxcode:bind-external-variables(
    $uri   as xs:string,
    $vars  as map(xs:string, xs:string)
  ) as xs:string {
    let $xqcode := unparsed-text($uri)
    return fold-left(
      map:keys($vars), $xqcode, function($string, $name) {
        let $value := replace($vars($name), ']``', '`{"]``"}`', 'q')
        return $string
        => replace('declare variable $' || $name || ' external;', '', 'q')
        => replace('$' || $name, '``[' || $value || ']``', 'q')
      }
    )
  };

_ example.xq _______

 declare variable $db external;
 count(collection($db))

_ run-bxcode.xq _______

  import module namespace bxcode = 'bxcode' at 'bxcode.xqm';
  bxcode:bind-external-variables('query.xq', map { 'db': 'BEP' })

_ output _______

  count(collection(``[BEP]``))

Cheers,
Christian

[1] https://www.mail-archive.com/basex-talk@mailman.uni-konstanz.de/msg09863.html