/til

TIL

Table of Contents

  1. Arch Linux
  2. Clojure
  3. Ecto
  4. Elixir
  5. Phoenix

Arch Linux

List packages installed from AUR

pacman -Qm

Regain disk space

Cleanup pacman cache

sudo pacman -Scc

Cleanup yay AUR cache

yay -Scc

Remove ~/.cache.

Clojure

Collections are functions

In Clojure collections are functions, so you can just call your map with a given key

user=> ({:a 1 :b 3} :b)
3

Your vector to take value at given index

user=> ([1 2 3 4 5] 3)
4

Or your set to verify if value is its member

user=> (#{1 2 3} 3)
3
user=> (#{1 2 3} 0)
nil

Ecto

insert/2 return values

When you call Ecto.Repo.insert/2 you can't expect to return either {:ok, struct} or {:error, error}. In case of connection connection failures/non existing table/DB errors Ecto will raise an exception.

From Ecto docs:

It returns {:ok, struct} if the struct has been successfully inserted or {:error, changeset} if there was a validation or a known constraint error.

Elixir

Shell history

In order to enable shell history add this to your ~/.bashrc (or ~/.zshrc or whatever you use)

export ERL_AFLAGS="-kernel shell_history enabled"

or for fish

set -x ERL_AFLAGS "-kernel shell_history enabled"

Pattern match on binaries

You can pattern match on binaries using this syntax

iex(2)> <<s::binary-size(6), " is ", rest::binary>> = "Elixir is so cool"
"Elixir is so cool"
iex(3)> s
"Elixir"
iex(4)> rest
"so cool"

This has some limitations like only the last binary can be without size, but has some cool things like binary-size being variable.

iex(1)> n = 6
iex(2)> <<s::binary-size(n), " is ", rest::binary>> = "Elixir is so cool"

More on that can be found in Elixir's special forms docs

Selecting records from mnesia

14
iex(7)> {ok, [grant]} = :mnesia.transaction(fn -> :mnesia.match_object({:my_table, 1, :_, :_, :_, :_, :_, :_, :_, :_, :_, :_, :_, :_, :_, :_, :_, :_, :_, :_, :_, :_, :_}) end)
{:atomic,
 [
   {:my_table, 1, "93585ef3-95c5-41cb-9b0f-c1522b95878f",
    "3c45caa6-c9e9-49a1-9df8-171d8665e24b",
    {{2020, 5, 21}, {14, 36, 23, 163447}},
    {{2020, 5, 21}, {14, 36, 23, 163450}}, "1253511464400978977",
    "63834ff4-0353-44e8-8ec2-e9585d0004e5",
    "fc574814-9b36-11ea-8f7e-02420a0f6e68", "data",
    "309d4055-2609-4205-a669-47160d6a51f0",
    "af1ef770-5765-4a8e-a5a4-ee187a8406dd",
    "data", true,
    1590093383, nil, "data", "data",
    "data", "data", "data", "initiated", %{}}
 ]}

Unfortunately you need to put there as many :_ as record have fields cause record in mnesia is just an ordered tuple (Don't know if it can be something else - probably yes- but in my case it was tuple, it was inserted by ecto_mnesia and I needed to select it in plain :mnesia).

Phoenix

App module name

You can supply various parameters to mix phx.new, one of them is --module which allows you to modify how your app's main module will be named. So if you have not straight mapping from underscore to camelcase you can supply your own.

mix phx.new nottrivial_app --module NotTrivialApp