fn:boolean

fn:boolean($arg as item()*) as xs:boolean

The function computes the effective boolean value of a sequence, defined according to the following rules. See also Effective Boolean Value.

• If $arg is the empty sequence, fn:boolean returns false.

• If $arg is a sequence whose first item is a node, fn:boolean returns true.

• If $arg is a singleton value of type xs:boolean or a derived from xs:boolean, fn:boolean returns $arg.

• If $arg is a singleton value of type xs:string or a type derived from xs:string, xs:anyURI or a type derived from xs:anyURI, or xs:untypedAtomic, fn:boolean returns false if the operand value has zero length; otherwise it returns true.

• If $arg is a singleton value of any numeric type or a type derived from a numeric type, fn:boolean returns false if the operand value is NaN or is numerically equal to zero; otherwise it returns true.

In all cases other than those listed above, fn:boolean raises a type error [ERRFORG0006].

The result of this function is not necessarily the same as $arg cast as xs:boolean. For example, fn:boolean("false") returns the value true whereas "false" cast as xs:boolean (which can also be written xs:boolean("false")) returns false.

let $abc := ("a", "b", "")

fn:boolean($abc) raises a type error [ERRFORG0006].

The expression fn:boolean($abc[1]) returns true().

The expression fn:boolean($abc[0]) returns false().

The expression fn:boolean($abc[3]) returns false().

fn:boolean([]) raises a type error [ERRFORG0006].