4.2. Sequence Types

All sequences match the sequence type item*.

Example 4.8. The most general sequence type: item*.

{ "foo" : "bar" } instance of item*,
() instance of item*,
([ 1, 2, 3 ], 2, { "foo" : "bar" }, 4)
    instance of item*

Results:

true
true
true

But sequence types can be much more precise than that. In general, a sequence type is made of an item type, as presented above, followed by an occurrence indicator among the following:

* stands for a sequence of any length (zero or more)
+ stands for a non-empty sequence (one or more)
? stands for an empty or a singleton sequence (zero or one)
The absence of indicator stands for a singleton sequence (one).

Example 4.9. Further sequence types.

( { "foo" : "bar" } , {} ) instance of object*,
() instance of object*,
( [ 1, 2, 3 ] , {} ) instance of json-item+,
[ 1, 2, 3 ] instance of array?,
() instance of array?,
"foo" instance of string

Results:

true
true
true
true
true
true

There is also a special type that matches only empty sequences, denoted () as well:

Example 4.10. Empty sequence type: ()

() instance of ()

Results:

true