Using Livebook as a Model

I have been having a quick experiment with livebook.

This is an interactive website that can be used to easily share Elixir code.
Think of it as Juypter Notebooks but with the backing system being Elixir rather than Python.

It has a very neat docker image:

docker run -p 8080:8080 livebook/livebook

This will stand up a local website running livebook. The console will give you a link (including a token) to allow you to access it.

You can create notebooks and add sections in Markdown or Elixir.
The great thing is that these can be interactively edited by multiple concurrent users.
You can also export a notebook as a file, publish the details and import it into another livebook.

I have been thinking about using this to recreate an old mac simulation tool. This tool allowed you to build a model with data flowing through it and you could use it to see bottlenecks.

I have three code blocks:

The first is the initialisation block


Agent.start_link(fn -> 0 end, name: :complete)
Agent.start_link(fn -> 0 end, name: :iteration)
Agent.start_link(fn -> 0 end, name: :qa_backlog)

The second is the update block

Agent.update(:iteration, fn x -> x + 1 end)
Agent.update(:complete, fn x -> x + min(10, Agent.get(:qa_backlog, & &1)) end)
Agent.update(:qa_backlog, fn value -> max(value - 10, 0) end )
Agent.update(:qa_backlog, fn value -> value + 20 end)

The third is the output block

:ok = IO.puts "Iteration #{Agent.get(:iteration, & &1)} Backlog #{Agent.get(:qa_backlog, & &1)} Complete #{Agent.get(:complete, & &1)}"

If you put the three blocks into livebook then you have the start of a model.

This is a very simplistic model. It attempts to show that the QA team will never be able to keep up with the two dev teams feeding it work. This could become far more sophisticated (with a random percentage of QA items failing and being returned to the teams). The idea here is to show how you can use an Agent in livebook.

I am going to see if you can add visualisations.

Announcing About

Last weekend I wrote and released the Elixir package called “about”.

This adds About topics to the iex environment.

It is installed in the usual way:

Add {:about, "~> 0.0.1"} to your deps list in mix.exs

Run mix deps.get

Run iex -S mix

You can now use help topics like:

iex(1)> h About.pipeline

I am looking for suggestions/contributions to the project.

It’s hosted on https://github.com/chriseyre2000/about and available on hex.pm and hexdocs.

Getting Started With Phoenix 1.4 (Part 3)

Continuing the way through the book.

Now have reached the end of Chapter 6.

This adds video to use associations. It includes some of the clever techniques that Phoenix uses to allow the templates to be customised.

By adding an action method you can customise the parameters passed to the various utility methods:

def action(conn, _) do args = [conn, conn.params, conn.assigns.current_user] apply(__MODULE__, action_name(conn), args) end

This allows details from the conn to be decomposed and passed as a parameter.

https://github.com/chriseyre2000/rumbl_1_4

Contentful to Neo4j in Elixir

I just finished an initial port of my neo4j to contentful library from Node to Elixir.

https://github.com/chriseyre2000/contentful_to_neo4j_ex

This is the same utility but in a very different language. It’s not quite as polished as the Node version (but won’t take long to catch up).

Issues that I have had during the port:

  • My machine had a very old erlang implementation (I had installed this when reading the Erlang chapter of 7 languages in 7 weeks – over 7 years ago) which broke HTTPoison, a fairly common HTTP library. The errors pointed to HTTPoison not working on a windows machine (which I have found to not be true).
  • The Contentful Elixir bindings are not very advanced. They don’t return the total number of items that you are paging through. It was not difficult to use the api directly.
  • There are lots of Elixir bindings for Neo4j. Very few of them are clearly documented for writing to Neo4j. Eventually I landed on bolt_sips. Bolt is too primitive, neo4j_sips uses a very old version of HTTPoison.

The Elixir error messages are incredibly clear.

Credo is great for ensuring best practices are applied.

Functional programming allows you to test real code without mocks or spend time fighting promises.

iex is a great REPL environment. You can recompile a module and carry on without restarting everything.

The code is self documenting. This is the top level method:

read_all_assets()
|> read_all_entries
|> process_contentful
|> write_to_neo4j
VSCode is a great editor for elixir. It’s great from the command line
code .
The above will open vscode on the project in the current directory.