Add public function for converting .livemd to .exs (#573)

lib/livebook.ex

@@ -0,0 +1,27 @@
+defmodule Livebook do
+  @moduledoc """
+  Livebook is an interactive notebook system for Elixir.
+
+  This module includes the public API.
+  """
+
+  @doc """
+  Parses the given Live Markdown document and converts it to Elixir
+  source code.
+
+  ## Limitations
+
+  Note that the resulting script may not compile in some cases, for
+  example if you define a macro in one cell and import it in another
+  cell, it works fine in Livebook, because each cell is compiled
+  separately. However, when running the script it gets compiled as a
+  whole and consequently doing so doesn't work.
+
+  Additionally, branching sections are commented out.
+  """
+  @spec live_markdown_to_elixir(String.t()) :: String.t()
+  def live_markdown_to_elixir(markdown) do
+    {notebook, _messages} = Livebook.LiveMarkdown.Import.notebook_from_markdown(markdown)
+    Livebook.Notebook.Export.Elixir.notebook_to_elixir(notebook)
+  end
+end

test/livebook_test.exs

@@ -0,0 +1,27 @@
+defmodule LivebookTest do
+  use ExUnit.Case, async: true
+
+  test "live_markdown_to_elixir/1" do
+    markdown = """
+    # Lists
+
+    ## Introduction
+
+    Let's generate a list of numbers:
+
+    ```elixir
+    Enum.to_list(1..10)
+    ```
+    """
+
+    assert Livebook.live_markdown_to_elixir(markdown) == """
+           # Title: Lists
+
+           # ── Introduction ──
+
+           # Let's generate a list of numbers:
+
+           Enum.to_list(1..10)
+           """
+  end
+end