Maps and match specs in elixir

ms_test.exs

defmodule MsTest do
  use ExUnit.Case
  doctest Ms

  @bob %{name: "Bob", job: "developer"}
  @alice %{name: "Alice", job: "musician"}
  @john %{name: "John", job: "musician"}
  @ada %{name: "Ada", job: "developer"}
  @alan %{name: "Alan", job: "developer"}
  @table :users

  setup_all do
    t = :ets.new(@table, [:ordered_set, :named_table])
    :ets.insert(t, {1, @bob})
    :ets.insert(t, {2, @alice})
    :ets.insert(t, {3, @ada})
    :ets.insert(t, {4, @john})
    :ets.insert(t, {5, @alan})
    :ok
  end

  test "all users" do
    q = [
      {
        {:_, :_},
        [],
        [{:element, 2, :"$_"}]
      }
    ]
    assert [@bob, @alice, @ada, @john, @alan] == :ets.select(@table, q)
  end

  test "users by name" do
    q = [
      {
        {:_, %{name: "Bob"}},
        [],
        [{:element, 2, :"$_"}]
      }
    ]
    assert [@bob] == :ets.select(@table, q)
  end

  test "all developers" do
    q = [
      {
        {:_, %{job: "developer"}},
        [],
        [{:element, 2, :"$_"}]
      }
    ]
    assert [@bob, @ada, @alan] == :ets.select(@table, q)
  end

  test "all developers - variant" do
    q = [
      {
        {:"$1", %{job: :"$2"}},
        [{:"==", :"$2", {:const, "developer"}}],
        [{:element, 2, :"$_"}],
      }
    ]
    assert [@bob, @ada, @alan] == :ets.select(@table, q)
  end

  test "all non developers" do
    q = [
      {
        {:"$1", %{job: :"$2"}},
        [{:"/=", :"$2", {:const, "developer"}}],
        [{:element, 2, :"$_"}],
      }
    ]
    assert [@alice, @john] == :ets.select(@table, q)
  end

  test "all developers, paginated" do
    q = [
      {
        {:_, %{job: "developer"}},
        [],
        [{:element, 2, :"$_"}]
      }
    ]
    {first_page, cont} = :ets.select(@table, q, 2)
    assert [@bob, @ada] == first_page
    assert {[@alan], :"$end_of_table"} == :ets.select(cont)
  end
end

@lessless Almost 4 years late, sorry. This query filters by job ("developer") and returns only the names as a list.

q = [
  {
    {:"$1", %{job: :"$2", name: :"$3"}},
    [{:==, :"$2", {:const, "developer"}}],
    [:"$3"]
  }
]