Function to read next non blank line from a file

Questions / Help
1

(Very experienced procedural programmer trying to learn elxir, so please excuse noob questions.)

Following on from my ‘how to read file line by line’ post.

Simple need, a function that returns the next non blank line from a file. Its already open, so I need pass the io returned from open as an arg. I know I need to recurse ( I think) but none of the ‘getting started with recursion in elixir’ articles help.

Non blank means len > 0 after strip all whitespace

1 Like
2

For these things you want to pattern match either by “\n” or ?\n

Also, before you start playing around with streams then I would recommend you to build a recursive function that walks the binary and accumulates the result to iodata.

It will teach you everything you’ll need to know and you can then apply it to streams.

3

sorry, my reference to prior post was misleading. I am not using streams. Just File.open and then IO.read(io, :line)

I am parsing line by line and need to ignore blank lines.

An example, or even a rough hint as to what the recursion would look like would really help.

4

Erlang has some nice docs: Constructing and Matching Binaries — Erlang System Documentation v28.0.2

In my post above I showed you how to match on newlines rather that be in a binary or an Erlang string aka charlist.

When you state that the line is blank I assume you mean that the line is just a new line: \n

5

its not the detection of blank line (I said what blank line means in this case in the question) I am stuck on, its the ‘looping’ . Anyway I asked gh copilot to do it for me, and I am embarrased that I couldnt work it out for myself

  def next_non_blank_line(io) do
    case IO.read(io, :line) do
      :eof ->
        :eof

      line ->
        if String.trim(line) == "" do
          next_non_blank_line(io)
        else
          line
        end
    end
  end
6

Yeah, you got it. Nothing to be embarrassed about, you’re learning a new language and a functional one.

Although, you can easily make the function branchless, not that you need it now, but I still recommend to take a look at the Erlang docs for building recursive functions.

Best of luck!

7

i want to get into good habits, how would you improve it, also pointers to recursion docs would be great, so many of them are either, factorial or similar things that I would have written recursively before.