Parsing a complex key = value structure with optional trailing comments

test_parser.ex

defmodule Test.Parser do
  import NimbleParsec

  # iex(9)> Test.Parser.parse """
  # ...(9)>   FOO = 1   (some foo)
  # ...(9)>   BAR = 2 (some
  # ...(9)>            bar)
  # ...(9)>   FAZ = 3 (some faz)
  # ...(9)> """
  # {:ok, ["FOO", 1, "somefoo", "BAR", 2, "somebar", "FAZ", 3, "somefaz"], "\n",
  # %{}, {4, 55}, 75}

  @space 0x0020
  @tab 0x009

  comment =
    lookahead_not(string(")"))
    |> optional(ignore(string(" ")))
    |> choice([
      ignore(string("(")),
      ignore(string("\n")),
      ignore(utf8_string([@space, @tab], min: 2)),
      utf8_string([], 1)
    ])
    |> repeat()
    |> ignore(string(")"))
    |> wrap()
    |> reduce({Enum, :join, [""]})

  start_comment =
    lookahead_not(string("("))
    |> concat(comment)

  no_comment =
    lookahead(string("\n"))
    |> string("")

  defparsec(
    :parse,
    eventually(utf8_string([?A..?Z, ?_], min: 1))
    |> eventually(integer(min: 1))
    |> choice([no_comment, start_comment])
    |> repeat()
  )
end