Exit a Recursive Function in Elixir

Question

I certainly have some catching up to do on understanding Recursion. I've got this

def query_url(id,page_number) do
 returned_response = HTTPoison.get! "https://some_web_page/#{id}/? pageNumber=#{page_number}"
  case returned_response.status_code do
    200 ->
      {:ok,returned_response.body}
    _ ->
      {:error,:not_found}
  end
end

... and

def recursive_function(id,page_number) do
   case query_url(id,page_number) do
     {:ok,response}  ->
        non_recusive_function(response)
        recursive_function(id,page_number + 1)
    {:error, :not_found} ->
        IO.puts "Exited"
   end
end

Assuming recursive_function(1234,1), It was my thinking that the recursive function would exit once query_url/2 returns {:error, :not_found}, but that's not the case, the recursive call does not exit.

All I'm trying to do is make a get request to a particular url, carry out some actions as long as 200 status was returned and exit once a non 200 status is returned.

The code looks correct to me. Can you try IO.inspecting every return value to make sure you do get the error case back? — Dogbert
– Dogbert, Commented May 1, 2017 at 7:34
@Dogbert, Issue was with the API provider, for whatever reason, they began returning 200 with an ERROR MESSAGE key where they hitherto returned 404. Thank you! — devie
– devie, Commented May 1, 2017 at 10:09
You might post the resolution you discovered in an answer and mark it as the answer so that others can see the question is now closed. — Scott Thompson
– Scott Thompson, Commented May 1, 2017 at 22:21
Highlights something useful to pay attention to, though... the base case should actually exit! (So you might want to put an upper limit on it or something) — Lamdas Everywhere
– Lamdas Everywhere, Commented May 2, 2017 at 2:31

devie · Accepted Answer · 2017-05-04 19:30:11Z

0

Thanks to @Dogbert, Issue was with the API provider, for whatever reason, they began returning 200 with an ERRORMESSAGE key in an ERRORARRAY map where they hitherto returned 404.

So replaced case with a cond

cond do
    returned_response.status_code == 200 and not returned_response["ERRORARRAY"] == []) ->
     {:ok,returned_response.body}
    returned_response.status_code == 400 -> 
     {:error,:not_found}

    true -> 
      {:error,:not_found}
end

answered May 4, 2017 at 19:30

devie

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