Reference · Lists

first

first(list | null) -> any

What it does

The first item of a list, or null when the list is empty. null counts as an empty list. xs[0] is the same thing for a list that is known to have an item.

Examples

print(first([1, 2, 3]))print(first(["ann", "bob"]))print(first(split("k=v", "=")))

1annk

Edge cases

• first([]) and first(null) are null, not an error. Give a default with ??.
• A first item that is null gives null too; check len when the difference matters.
• The item comes back as it is: a list inside a list stays a list.

print(first([]), first(null), first([]) ?? 0)print(first([null, 1]), len([null, 1]) > 0)print(first([[1, 2], [3]]))

null null 0null true[1, 2]

Errors

An argument that is not a list or null is a runtime error, not an error value. A string is not a list: use take or slice for its first characters.

print(first("abc"))

line 1: `first` expects a list as argument 1, got str

Chaining

In a pipeline first takes the list and needs no arguments: the smallest after a sort, the first match after a filter.

print([5, 3, 9] | sort | first)print(["pear", "fig", "apple"] | sort_by(len) | first)print([1, 2, 3] | filter((x) => x > 5) | first ?? "none")

3fignone

See also

last, find, take, slice, min

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