José,
thanks for taking the time to respond to my somewhat rambling comment. To be honest, if I had a clear idea on how to solve some of these things I would have done it - but i'm still a novice at the otp ecosystem in general.

Maybe it's easier for me to walk through what I do, so I can show you where I run into problems. One of my favourite ways to learn a new language is in a REPL. I've used a lot of them in the past, and iex is pretty good. Pry (in ruby) is probably the gold standard.

Interactive Elixir (1.5.0) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> 1 / 0
** (ArithmeticError) bad argument in arithmetic expression
:erlang./(1, 0)

This is pretty good. Now we can move on to pry

[1] pry(main)> 1 / 0
ZeroDivisionError: divided by 0
from (pry):1:in `/'

The beauty here is it's saying the same thing, but the information is slightly more precise and it tells me clearly that the function being executed came from (pry) which makes a load of sense to someone using pry. I know this is a basic example, but in elixir, as you start spawning more and more processes, deciphering the log messages gets harder.

back to iex

Task.async(fn -> 1 / 0 end)
** (EXIT from #PID<0.94.0>) evaluator process exited with reason: an exception was raised:
** (ArithmeticError) bad argument in arithmetic expression
:erlang./(1, 0)
(elixir) lib/task/supervised.ex:85: Task.Supervised.do_apply/2
(elixir) lib/task/supervised.ex:36: Task.Supervised.reply/5
(stdlib) proc_lib.erl:247: :proc_lib.init_p_do_apply/3

07:34:45.847 [error] Task #PID<0.97.0> started from #PID<0.94.0> terminating
** (ArithmeticError) bad argument in arithmetic expression
:erlang./(1, 0)
(elixir) lib/task/supervised.ex:85: Task.Supervised.do_apply/2
(elixir) lib/task/supervised.ex:36: Task.Supervised.reply/5
(stdlib) proc_lib.erl:247: :proc_lib.init_p_do_apply/3
Function: #Function<20.99386804/0 in :erl_eval.expr/5>
Args: []

This is scary. Why's it repeated? why does one have a timestamp? how does "lib/task/supervised.ex:85: Task.Supervised.do_apply/2" get here ? I called Task.async which doesn't show in the messages?

I want to reiterate at this point that it's not that bad, I think the repl is pretty good but the error messages just leave a bit to be desired. Maybe there is an article on deciphering them? But if you need that, I'll say it's a barrier.

In terms of the formatter, I need to go through my old code to remember where all those particular hurdles were, but someone has suggested a prebuilt json formatting logger which sounds good to me.

A sweet spot for Elixir (for me) is queue processing, in an autoscale group on AWS. So I have a real application in mind, and I originally knocked it up with hardly any knowledge and using genstage for back-pressure etc. in a couple of nights. This is saying a great thing about the language. But then shipping logs, deployment, debugging (if i deploy with distillery it locks up, and it has slow memory leak that makes no sense to me), dockerising, handling autoscale events have all stopped it from going to production ready.

> Where would you expect to find this information? Did you see `mix run` at all? Maybe in the escripts page we should point to `mix run` as it seems an `escript` is really not required in your case?

A guide on https://elixir-lang.org/getting-started/introduction.html would be great, to just give the different options and when you'd use them. Maybe something like "The anatomy of an elixir application" (or program because application is overloaded).

For me it is the cyclic journey through the different ways to do things. So it took a while to work out that I can't just pass in command line parameters to mix run, so the application gets them. Unless i'm wrong?

In escripts I can. And they will start the application automatically. Why would I use them? And what's the difference between them and running mix run lib/script.exs?

So then I started thinking - maybe the ideal way is to have an application running in the --no-halt way like you've described and have an escript connect to it to pass in configuration changes. But i'm just hacking different ways rather than learning from an example or best practice. I'd love config to be changeable on the fly for a daemon / application.

> Which kind of information do you need?
(re: run time vs compile time)

in my limited experience, config.exs pulls in config params at compile time. I thought it would happen at run time because it's a script (exs). I know phoenix has a way of dealing with this, but i haven't gone fully down that rabbit hole yet, because I'm not even sure if config.exs is right for my requirements. If I want it to be hot loaded, I'm thinking I need a genserver with the config as its state, and some way to communicate changes to it - either from the file system or an escript.

> Those particular error message were fixed in Elixir v1.5

Thank you, it sounds like a great release

I'll open that issue, and check out your new book too because I really think there are huge gaps between

1) I can write genservers and get that

2) I know the tradeoffs and best structure for my supervision tree (especially with things like OS signals thrown in the mix)

3) I can deploy this into production

4)

5)

6) I can leverage distributed features