Gleam ✨

Gleam is a statically typed functional programming language for building scalable concurrent systems. It compiles to Erlang and has straightforward interop with other BEAM languages such as Erlang, Elixir and LFE.

pub enum Tree(value) =
  | Leaf(value)
  | Node(Tree(value), Tree(value))

pub fn any(tree: Tree(a), check: fn(a) -> Bool) -> Bool {
  case tree {
  | Leaf(i) -> check(i)
  | Node(left, right) -> any(left, check) || any(right, check)
  }
}

pub fn has_even_leaf(tree: Tree(Int)) -> Bool {
  any(tree, fn(i) {
    i % 2 == 0
  })
}

For more information see the Gleam website: https://gleam.run.