Presentation #17
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#+TITLE: Practicing Elixir by building concurrent, distributed, multiplayer games in the terminal
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#+TITLE: Practicing Elixir by Building Concurrent, Distributed, Multiplayer Games in the Terminal
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#+AUTHOR: Lizzy Hunt (Simponic)
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#+AUTHOR: Lizzy Hunt (Simponic)
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* Introduction
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* Reminder: linux.usu.edu
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This meeting should be being streamed live, at [[https://linux.usu.edu/streams]].
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This meeting should be being streamed live at [[https://linux.usu.edu/streams]].
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* Introduction
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#+BEGIN_SRC elixir
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#+BEGIN_SRC elixir
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defmodule Hello do
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defmodule Hello do
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def hello() do
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def hello() do
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@ -20,18 +21,37 @@ CheSSH is a multiplayer distributed game of chess over SSH - let's take a quick
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[[https://chessh.linux.usu.edu]]
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[[https://chessh.linux.usu.edu]]
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* Elixir - Functional Meta-Programming
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* Elixir - Functional Programming & Meta-Programming
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Elixir is a self-proclaimed "dynamic, functional language for building scalable and maintainable applications".
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Elixir is a self-proclaimed "dynamic, functional language for building scalable and maintainable applications". Obviously, one of Elixir's
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Obviously, one of Elixir's main selling points must be its functional paradigm - its the second in the list.
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main selling points is that of its functional paradigm - it's the second in the list.
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We'll take a quick look at some features of Elixir, and find that functional programming brings a lot to the table.
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We'll take a quick look at some features of Elixir, and find that functional programming brings a lot to the table.
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** Basic Data Types
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1. ~int~s, ~bool~s, ~string~s are all here
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+ ~1~, ~true~, ~"Hello"~
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2. Atoms: prefixed with ":" are named constants whose name is their value, similar to symbols in LISP
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+ ~:x~, ~:three~
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4. Maps: regular key-value store; keys can be literally anything, including other maps
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+ ~%{%{a: 1}: 2, %{a: 2}: :an_atom}~
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5. Lists: lists are singly-linked elements of "stuff"
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+ ~[1,2,3]~, ~[]~, ~[1, [2, :three, %{}]]~
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6. Tuples: tuples are fixed-size collections of "stuff"
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+ ~{1,2,3}~, ~{1, {2, 3}}~
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** Pattern Matching
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The match operator "=" does not mean its convential meaning of assignment, but instead an assertion of equivalence.
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This gives way to one of Elixir's unique features of pattern matching similar to that found in Rust's ~match~ or Scala's ~case~.
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* Elixir - Concurrency
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* Elixir - Concurrency
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Elixir is built on top of (and completely interoperable with) Erlang - a language developed to build massively fault-tolerant systems in the 80's
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Elixir is built on top of (and completely interoperable with) Erlang - a language developed to build massively fault-tolerant systems in the 80's
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for large telephone exchanges with hundreds of thousands of users.
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for large telephone exchanges with hundreds of thousands of users.
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You can imagine (if you look past the many problems with this statement), Elixir and Erlang to be analogous to Python and C,
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You can imagine (if you look past the many problems with this statement), Elixir and Erlang to be analogous to Python and C, respectively - but
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respectively - but without the massive performance penalty.
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without the massive performance penalty.
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** The BEAM
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** The BEAM
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The BEAM powers Elixir's concurrency magic; by running a VM executing Erlang bytecode that holds one OS thread per core,
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The BEAM powers Elixir's concurrency magic; by running a VM executing Erlang bytecode that holds one OS thread per core,
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@ -41,7 +61,7 @@ Imagine an army of little goblins, and you give each a todo list. The goblins th
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suited for them, and have the added benefit that they can talk to each other.
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suited for them, and have the added benefit that they can talk to each other.
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** Concurrency - Demo!
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** Concurrency - Demo!
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Here we will open up two terminals: one running an Elixir REPL on my machine, and another to SSH into my android here
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Here we will open up two terminals: one running an Elixir REPL on my machine, and another to SSH into my android:
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#+BEGIN_SRC python
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#+BEGIN_SRC python
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import subprocess
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import subprocess
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@ -79,7 +99,9 @@ Here we will open up two terminals: one running an Elixir REPL on my machine, an
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System.cmd("espeak", [msg])
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System.cmd("espeak", [msg])
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end
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end
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end
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end
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#+END_SRC
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#+BEGIN_SRC elixir
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defmodule KVServer do
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defmodule KVServer do
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require Logger
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require Logger
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@max_len_msg 32
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@max_len_msg 32
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@ -133,8 +155,8 @@ This demo shows how we can:
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* CheSSH
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* CheSSH
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With a very brief and quick exploration into concurrency with Elixir, we can now explore the architecture of CheSSH,
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With a very brief and quick exploration into concurrency with Elixir, we can now explore the architecture of CheSSH,
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and how it came to be on 5 raspberry pis
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and the hardware cluster it runs on:
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