Skip to content
Gale

Lists

List<A> is an ordered, immutable list of values of type A. Use [] for an empty list and [head | tail] to prepend an element. Pattern matching separates the empty and non-empty cases:

mod lists


alias gale_std.list


pub fn prepend(value: Integer, values: List<Integer>) -> List<Integer> {
  [value | values]
}


pub fn first(values: List<Integer>) -> Option<Integer> {
  case values {
    [] -> None
    [head | _] -> Some(head)
  }
}


pub fn double_positive(values: List<Integer>) -> List<Integer> {
  values
    |> list.filter(fn(value: Integer) -> value > 0)
    |> list.map(fn(value: Integer) -> value * 2)
}

gale_std.list owns both structural operations such as first, length, and reverse and eager transformations such as map, filter, and reduce. Each operation returns a value; it does not change the original list. See the standard library for more operations.