Elixir beginner: early exit efficiency in map creation

Questions & Help Questions
4

You can do

is_palindrome? = fn (n) -> s = to_string(n); s == String.reverse(s) end

try do
  for x <- 999..100, y <- 999..x, n = x * y, is_palindrome?.(n), do: throw(n)
catch 
  n -> n
end

which is the equivalent of your second example.

However, that will not find the largest palindrome. To do that you want

Enum.reduce_while 999..100, 0, fn
  x, highest when highest >= x * 999 -> {:halt, highest}
  x, highest ->
    highest =
      Stream.map(999..x, &(x * &1))
      |> Enum.reduce(highest, &(&1 > &2 && is_palindrome?.(&1) && &1 || &2))
    {:cont, highest}
end