dogweather

Dbg() in a `with` sequence?

dbg() is one of my favorite Elixir features: placing it somewhere in a pipe of function calls outputs all the intermediate results. It’s great for debugging parsing code. Like this:

    meta_date =
      document
      |> Floki.find("meta[property='article:published_time']")
      |> Floki.attribute("content")
      |> List.first()
      |> parse_date_text()
      |> dbg()

Well, now I’m starting to use with instead of |>. Is it possible to get that dbg() behavior? I haven’t figured it out. For example:

  @spec parse_human_date_string(binary) :: nil | Date.t
  def parse_human_date_string(text) when is_binary(text) do
    with [_, raw_month, raw_day, year] <- Regex.run(~r/^(.+) (.+), (\d\d\d\d)$/, text),
          day        <- String.pad_leading(raw_day, 2, "0"),
          month_num  <- Integer.to_string(Enum.find_index(@months, &(&1 == raw_month)) + 1),
          month      <- String.pad_leading(month_num, 2, "0"),
         {:ok, date} <- Date.from_iso8601("#{year}-#{month}-#{day}"),
         dbg() do  ### THIS IS WHAT I'D LIKE TO DO ###
      date
    else
      _ -> nil
    end
  end

Then I’d get the results of each “line” of the with.

6 comments

#debugging #with

0 894 6

2023-12-27 00:37:18 UTC

Marked As Solved

dogweather

Yep, just make dbg() one of the clauses. I’ll paste here the actual running code and the output. I’m pretty sure it’s the same as above:

  @spec parse_human_date_string(binary) :: Date.t | nil
  def parse_human_date_string(text) when is_binary(text) do
    with [_, raw_month, raw_day, year] <- Regex.run(~r/^(.+) (.+), (\d\d\d\d)$/, text),
          day        <- String.pad_leading(raw_day, 2, "0"),
          month_num  <- Integer.to_string(Enum.find_index(@months, &(&1 == raw_month)) + 1),
          month      <- String.pad_leading(month_num, 2, "0"),
         {:ok, date} <- Date.from_iso8601("#{year}-#{month}-#{day}"),
         dbg() do
      date
    else
      _ -> nil
    end
  end

~/s/P/oregon-revised-statutes-crawler ❯❯❯ mix test                                                       refactor ✱
Compiling 1 file (.ex)
Generated crawlers app
................................................................................................................................[lib/news/date_modified.ex:99: News.DateModified.parse_human_date_string/1]
binding() #=> [
  date: ~D[2023-12-05],
  day: "05",
  month: "12",
  month_num: "12",
  raw_day: "5",
  raw_month: "December",
  text: "December 5, 2023",
  year: "2023"
]

..........[lib/news/date_modified.ex:99: News.DateModified.parse_human_date_string/1]
binding() #=> [
  date: ~D[1997-05-26],
  day: "26",
  month: "05",
  month_num: "5",
  raw_day: "26",
  raw_month: "May",
  text: "May 26, 1997",
  year: "1997"
]

..[lib/news/date_modified.ex:99: News.DateModified.parse_human_date_string/1]
binding() #=> [
  date: ~D[2020-01-01],
  day: "01",
  month: "01",
  month_num: "1",
  raw_day: "1",
  raw_month: "January",
  text: "January 1, 2020",
  year: "2020"
]

.......
Finished in 0.9 seconds (0.4s async, 0.5s sync)
17 doctests, 130 tests, 0 failures

Post #3

Also Liked

dogweather

Never mind—it freakin’ works. Amazing.

Post #1

dogweather

BTW, @josevalim this is mind-blowingly good.

Post #4

sodapopcan

OIC, dbg() without explicit args (or pipe) just outputs the current binding which I never realized before.

For example:

if true do
  a = 1
  dbg()
end
binding() #=> [a: 1]

Cool!

PS, I wasn’t able to get it to work before because I was being dumb and trying this: with 1 <- 1, 2 <- 2, dbg(), do: "hi" so of course I got binding() #=> []