[Proposal] Double pipeline operator ||>

[t...@scalpel.com]

The pipeline operator is one of the best features of the language, however there are some instances where you want to continue a chain of pipelines for clarity but can't because the argument order is not conducive to piping. For example here is an example when working with files:

defmodule Chess.PGN do

  def unique_checkmates(input_path, output_path)

    path

    |> File.stream!()

    |> Stream.chunk_every(21)

    |> Stream.filter(fn chunk -> checkmate?(Enum.at(chunk, 17)) end)

    |> Stream.uniq_by(fn chunk -> Enum.at(chunk, 19) end)

    |> Stream.map(fn chunk -> Enum.join(chunk, "") end)

    |> Enum.join("")

    |> write_file(output_path)

  end

  

  def write_file(content, output_path) do

    File.write!(output_path, content)

  end

end

Instead of having to add a dummy method I would like to double pipe into File.write which would be cleaner.

  ...

  ||> File.write!(output_path)

I think this could also be extended to triple, and quadruple pipes. Five seems like overkill, but I think you could make the argument for arbitrary levels of piping.

[José Valim]

Hi Tom,

Extensions to the pipe operator have been proposed multiple times and always rejected. I recommend reading previous discussions for more information.

Have a good one,

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

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[Louis Pilfold]

Hi Tom!

While it will not be added to core there is no reason why you couldn't implement this functionality in your application or as a library.

Elixir does allow custom operators, though the ones you can use is limited so you won't be able to use `||>` `|||>` etc. Perhaps instead your macro could use a placeholder to indicate where the value should be inserted:

   data |> File.write!(path, _)

or

   data >>> File.write!(path, _)

Cheers,

Louis

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[Ricardo Harari]

Hi Tom

the order of the argument breaks sometimes and define an auxiliary function makes the code more readable.

for this sample you can simplify

...

|> (content fn -> File.write! (output_path, content) end).

but it will be more readable if we can write something like:

|> File.write! (Output_path, &1)

with macros you can invent your own pipe

see this project as an inspiration: https://github.com/ruby2elixir/plumber_girl

have fun!

--

[Ricardo Harari]

oops...little mistake

...

|> (fn content -> File.write! (output_path, content) end).