empty
The empty value, represented by _, is a placeholder indicating absence of a value, missing data, or an intentionally ignored element. It is used to represent missing values in tables and skipped elements in tuple destructuring.
Syntax
An empty value is written using one or more underscores _:
____
Kind
The kind of an empty value is just empty:
<_>
Empty values in arrays and matrices
When an array or matrix literal includes _, the element kind becomes optional.
For example, this row vector has kind <[f64?]:1,4>:
x:=[
1
2
_
5
]You can also use optional element kinds explicitly:
x<[u64?]>:=[
_
2u64
_
3u64
_
4u64
]unwrapped<[u64]>:=x?├ x ⇒ x
└ * ⇒ 0u64.
unwrapped evaluates to [0 2 0 3 0 4].