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boolean

The boolean function in XQuery is used to convert its argument to a boolean value according to specific rules.

fn:boolean(arg)

The following table describes the argument for this command:

Argument	Required/ Optional	Description
arg	Required	The sequence to be converted into a boolean. It can be an atomic value, a sequence of nodes, or an empty sequence. It can contain zero or more items.

If the sequence is empty, the result is

false

If the sequence contains a single boolean value, that value is returned.

If the sequence contains a single numeric value,

false

is returned for

NaN

, and

true

for any other numeric value.

If the sequence contains a single string,

false

is returned for an empty string, and

true

for any other string.

For nodes, the existence of nodes in a sequence determines the truth value:

true

for a non-empty sequence, and

false

for an empty one.

If the sequence contains more than one item and none of these conditions apply, an error occurs.

The following table lists some sample values and return values:

Input	Return Value
fn:boolean( () )	false
fn:boolean('')	false
fn:boolean(0)	false
fn:boolean('0')	true
fn:boolean('false')	true
fn:boolean(("Hello"))	true
fn:boolean(xs:float('NaN'))	false
fn:boolean($ordDoc/order[1])	true
fn:boolean($ordDoc/noSuchChild)	false
fn:boolean(<a>false</a>)	true