{-- IfExpr using built in function contains() --}

<result>
{
for $a in document("data/R-items.xml")//item_tuple
return
  <my_item>
  {
    $a/description,
    <cycle>
    {
      if (contains($a/description, "cycle")) then "YES"
        else "NO"
    }
    </cycle>
  }
  </my_item>
}
</result>

---

{-- nested if-then-else --}

<result>
{
for $a in document("data/R-items.xml")//item_tuple
return
  <my_item>
  {
    $a/description,
    $a/reserve_price,
    <cycle>
    {
      if (contains($a/description, "cycle"))
      then
        if (number($a/reserve_price) < 200)
        then
          "Cycle less than 200"
        else
          "Cycle greater or equal 200"
      else
        if (number($a/reserve_price) < 200)
        then
          "Not a cycle and cheap"
        else
          "Not a cycle, but expensive"
    }
    </cycle>
  }
  </my_item>
}
</result>

---

{-- deeply nested if-then --}

<result>
{
for $a in document("data/parts-data.xml")//part
return
  if ($a/@name = "car")
  then <my_car> { $a/@* } </my_car>
  else if ($a/@name = "engine")
  then <my_engine> { $a/@* } </my_engine>
  else if ($a/@name = "door")
  then <my_door> { $a/@* } </my_door>
  else if ($a/@name = "piston")
  then <my_piston> { $a/@* } </my_piston>
  else if ($a/@name = "window")
  then <my_window> { $a/@* } </my_window>
  else if ($a/@name = "lock")
  then <my_lock> { $a/@* } </my_lock>
  else if ($a/@name = "skateboard")
  then <my_skateboard> { $a/@* } </my_skateboard>
  else if ($a/@name = "board")
  then <my_board> { $a/@* } </my_board>
  else if ($a/@name = "wheel")
  then <my_wheel> { $a/@* } </my_wheel>
  else if ($a/@name = "canoe")
  then <my_canoe> { $a/@* } </my_canoe>
  else
    <my_unknown/>
}
</result>

---

{-- boolean expr: udf returning boolean --}

define function isEven(integer $n) returns boolean
{
  if (($n mod 2) = 0) then true() else false()
}

<result>
{
  for $n in document("data/parts-data.xml")//part/@partid
  return
    <test>
    {
      concat(string($n), if (isEven($n)) then " is even"
        else " is odd")
    }
    </test>
}
</result>

---

{-- boolean expr: udf returning boolean from FLWR expr --}

define function hasInstrument($action as node) as xs:boolean {
  let $instrument := $action/instrument
  return
    if ($instrument) then true() else false()
}

<result>
{
  for $a in document("data/seq-data.xml")//action
  return
    <my_action>
    {
      $a,
      <has_instrument>
      {
        if (hasInstrument($a)) then "YES" else "NO"
      }
      </has_instrument>
    }
    </my_action>
}
</result>