This is an example to illustrate the usage of the context item `.` in functions in records that are annotated with `%method`.

geom-vector.xq

(:~
 : Example of context item in functions annotated with %method in a record
 : The geom:vector has three methods that operate on the record instance
 : ?dimension() can be thought of as a computed value
 : ?fill($dimension) is a helper function that is then used in
 : ?plus($other) adds another geom:vector to this instance
 :)
declare record geom:vector(
  values as xs:double+,

  dimension as fn() as xs:positiveInteger := %method fn() { count(?values) },

  fill as fn($dimension as xs:positiveInteger) as geom:vector := %method fn ($dimension) {
    let $current-dimension := ?dimension()
    return
      if ($current-dimension > $dimension) then error() 
      else if ($current-dimension = $dimension) then .
      else map:put(., "values", ( ?values, $current-dimension to $dimension - 1 ! 0 ))
  },

  plus as fn($other as geom:vector) as geom:vector := %method fn($other) {
     let $max-dimension := math:max((?dimension(), $other?dimension()))
     return map:put(., "values", for-each-pair(
        ?fill($max-dimension)?values,
        $other?fill($max-dimension)?values,
        op("+"))
  }   
);

geom:vector((-1, 1, 0))
  ?plus(geom:vector((1, -1)))
  ?values

(: yields the vector sum 
(0, 0, 0)
:)