XQuery for eXist - eXist: A NoSQL Database and Application Development Platform - page 114

let $ f := upper-case # 1
return
local:map-example ( $ f , ( "Hello" , "world!" ))
We first define a function, local:map , that runs the function passed in its first
parameter, $func , over all members of its second operand, $list .
We then assign the upper-case function to $f . The #1 after the function name
means that we want the upper-case function with only one parameter (in case
there are more).
Finally, we call local:map with our function and some input strings. It returns
the expected HELLO WORLD! .
Higher-order functions is a serious subject in its own right and includes topics such
as: inline and partial functions, closures, currying, and more. For further informa‐
tion, you can refer to the XQuery 3.0 specification and to this excellent eXist wiki
article .
The simple map operator
The XQuery 3.0 bang operator ! (or simple map operator, as it is officially called) can
be seen as a shorthand for simple FLWOR expressions. It applies the right-hand
expression to each item in the sequence gained from evaluating the left-hand expres‐
sion. For instance:
( 1 to 10 ) ! . + 1
is the same as:
for $ i in ( 1 to 10 ) return $ i + 1
The string concatenation operator
The string concatenation operator || is a shorthand replacement for the concat
function: it concatenates strings. For example, the following expression will be true:
'Hello ' || 'world' eq concat ( 'Hello ' , 'world' )
Annotations
XQuery 3.0 allows annotations for functions and variables. This is used, for instance,
to make them private (visible only in the enclosing module) or public:
declare %private variable $ myns:only-i-can-see-this := 'secret' ;
declare
%public
function myns:do-something-public () {