MarkLogic 9 Product Documentation

fn:boolean

fn:boolean(
   $arg as item()*,
   [$collation as xs:string]
) as xs:boolean

Summary

Computes the effective boolean value of the sequence $arg. See Section 2.4.3 Effective Boolean Value[XP].

Usage Notes

When using XQuery version "1.0-ml", this function implements the semantics from May 2003.

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 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 other cases, fn:boolean raises a type error [err:FORG0006] when run in XQuery strict mode (1.0).

The static semantics of this function are described in Section 7.2.4 The fn:boolean function[FS].

Note:

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 returns false.

Example

xquery version "1.0";
let $x := ("a", "b", "c")
return
fn:boolean($x)
=> raises a type error [err:FORG0006].

xquery version "1.0-ml";
let $x := ("a", "b", "c")
return
fn:boolean($x)
=> true

let $x := ("a", "b", "c")
return
fn:boolean($x[1])
=> returns true.

let $x := ("a", "b", "c")
return
fn:boolean($x[0])
=> returns false.