Sequence Functions

Sequence & Higher-Order Functions

Sequence Operations

Function	Description
`boolean($arg)`	Effective boolean value
`count($arg)`	Number of items
`data($arg?)`	Typed values (atomization)
`deep-equal($a, $b)`	Deep structural equality
`distinct-values($arg)`	Remove duplicates
`empty($arg)`	True if empty
`exists($arg)`	True if not empty
`exactly-one($arg)`	Assert exactly one item
`one-or-more($arg)`	Assert at least one item
`zero-or-one($arg)`	Assert at most one item
`head($arg)`	First item
`tail($arg)`	All items except first
`index-of($seq, $search)`	Positions of $search in $seq
`insert-before($target, $pos, $inserts)`	Insert items at position
`remove($target, $pos)`	Remove item at position
`reverse($arg)`	Reverse order
`subsequence($source, $start, $length?)`	Contiguous subsequence
`unordered($source)`	Implementation-dependent order
`sort($input, $collation?, $key?)`	Sort (numeric or string, optional key function)
`true()`, `false()`, `not($arg)`	Boolean functions
`last()`, `position()`	Context position and size

for-each($seq, $action) — Apply function to each item.

for-each(1 to 5, function($x) { $x * $x })
(: 1, 4, 9, 16, 25 :)

filter($seq, $predicate) — Keep items where predicate is true.

filter(1 to 10, function($x) { $x mod 2 = 0 })
(: 2, 4, 6, 8, 10 :)

fold-left($seq, $zero, $f) — Left fold (reduce).

fold-left(1 to 5, 0, function($acc, $x) { $acc + $x })
(: 15 :)

for-each-pair($seq1, $seq2, $action) — Apply function to pairs.

for-each-pair((1,2,3), (10,20,30), function($a,$b) { $a + $b })
(: 11, 22, 33 :)

apply($function, $array) — Call function with arguments from array.

apply(concat#3, ["a", "b", "c"])    (: "abc" :)

sort(("banana", "apple", "cherry"), (), function($x) { string-length($x) })
(: "apple", "banana", "cherry" :)

Function	Description
`function-lookup($name, $arity)`	Look up function by QName and arity
`function-name($func)`	QName of a named function
`function-arity($func)`	Arity of a function

let $f := function-lookup(xs:QName("fn:abs"), 1)
return $f(-42)                              (: 42 :)

Function	Description
`error($code?, $description?, $value?)`	Raise an error
`trace($value, $label?)`	Returns $value unchanged (debug)