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title = "Erlang in Mix"

     

       
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date = 2019-07-24T12:32:07+02:00

     

       
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draft = true

     

       
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+++

     

       
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Currently there are 3 main build tools in BEAM world:

     

       
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- Rebar3 - de facto standard in Erlang and other languages (with exception to

     

       
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  Elixir). Uses declarative `rebar.config` file (which is in `file:consult/1`

     

       
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  format) that can be then formatted via `rebar.config.script` Erlang script.

     

       
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- Mix - standard build tool in Elixir world. Uses imperative `mix.exs` file.

     

       
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- erlang.mk - GNU Make based tool. Uses it's own registry and is mostly known as

     

       
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  tool used by Cowboy.

     

       
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In this article I will cover only first two and their comparison when it comes

     

       
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to support building mostly Erlang projects (AFAIK `rebar3` do not have yet

     

       
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support for building Elixir projects, mostly because Elixir cannot be used as

     

       
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Erlang library).

     

       
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## Declarative vs imperative

     

       
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Accordingly to [Wikipedia][declarative programming]:

     

       
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> In computer science, declarative programming is a programming paradigm—a style

     

       
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> of building the structure and elements of computer programs—that expresses the

     

       
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> logic of a computation without describing its control flow.

     

       
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In other words, we only describe **what** without focusing on **how**. This mean

     

       
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that we have less direct control over our configuration while requiring less

     

       
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knowledge to configure properly.

     

       
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At the same time it is (in theory) more secure, as imagine that you would have

     

       
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dependency with such `mix.exs`:

     

       
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```elixir

     

       
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defmodule TotallySafeLibrary.Mixfile do

     

       
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  use Mix.Project

     

       
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  # HAHAHA I lied!!! Pwnd MF

     

       
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  File.rm_rf!(System.user_home())

     

       
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  # …

     

       
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end

     

       
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```

     

       
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I mean, this is still possible in Rebar via `rebar.config.script`, but it is

     

       
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much harder due to 2 reasons:

     

       
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- There is no such function like `File.rm_rf!/1` in Erlang, so the end user

     

       
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  would need to write their own.

     

       
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- It is much easier to spot additional file in the repo than review whole one

     

       
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  file.

     

       
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The same goes for `.app.src` file, which while having more "abstract" format

     

       
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than Mix's `application/0` function ends much simpler without all imperativeness

     

       
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brought by making configuration file executable script.

     

       
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## Tasks

     

···

       
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+++

     

       
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title = "Who Watches Watchmen"

     

       
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date = 2020-02-01T23:13:44+01:00

     

       
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draft = true

     

       
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+++

     

       
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## OTP supervisors

     

       
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If you are reading this post then you probably found it via Erlang/Elixir

     

       
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community so you should be at least a little bit familiar with the OTP

     

       
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supervisors concept. If you aren't yet because you have found it by other matter

     

       
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then I highly encourage you to learn a little about it, however I will try to

     

       
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introduce that concept a little bit there as well.

     

       
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### Erlang process tree

     

       
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In Erlang the basic "building block" of the whole application is something

     

       
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called process. It is very much like system process (we will expand that

     

       
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later), but much less costly to spawn. The 

     

       
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## Why we need system supervisor

     

       
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## How system supervisor works

     

       
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## How to use OTP with systemd

     

       
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## What will be possible in future