Intro to Elixir - Speaker Deck

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Intro to Elixir from a   scripting language perspective

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Matthew Lyon @mattly Ruby, Javascript/ CoﬀeeScript, Bash, Python, SQL, Max/MSP

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What can this help me build? 2004, Rails: Web + SQL 2006, jQuery: sane frontend 2010, node: concurrent…?

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What can this help me build? easily scalable software that doesn’t wake me up at 3am

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erlang is awesome

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erlang is awesome the VM

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concurrency model lightweight processes actor pattern

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OTP: “killer app” design principles library used to build systems w/ 99.9999999% uptime

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syntax is… weird has a lot of gotchas {foo, State}:bar(1,2) foo:bar(1,2,{foo, State}) →

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stdlib interfaces many inconsistencies ! lists:map(Fun, List) -> List2 string:substr(Str, Start, Length) -> SubString !

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Ralph Waldo Emerson “Consistency is the hobgoblin of little minds.”

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“Inconsistency is the hobgoblin of unmaintainable software.”

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goto fail heartbleed !

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Elixir created by rails-core   member Jose Valim

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kinda like coﬀeescript but not really

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plain syntax is   easier to read and reduces gotchas

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thing, arguments ! Enum.map(list, fun) -> list2 String.slice(str, start, len) -> substr stdlib interfaces   are consistent

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metaprogramming there when you want it, transparent when you don’t

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it has amazing tooling  great build system  documentation  doctests dependency management included testing library

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it’s erlang semantics ! not ‘ruby compiling to erlang’ “CoﬀeeScript is just Javascript”

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it compiles to erlang bytecode, integrates w/ existing ecosystem ! though you’ll have to learn a bit of erlang too ! similar to Clojure, Scala

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unlearn you   some OOP   for great good

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object-oriented is not the only good way to design software

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functional programming doesn’t have to be mathematical or complex

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assignment & control flow are not essential to programming

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locks & semaphores   are not essential to concurrency

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functional programming   treats computation as the evaluation of mathematical functions and avoids state and mutable data. Functional programming emphasizes functions that produce results that depend only on blah blah expressions blah blah blah declarative blah blah blah no side eﬀects blah blah blah lambda calculus blah blah blah monads blah blah blah category theory source: wikipedia

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functions transform  data

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functions are small, focused grep '/home' /etc/passwd

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functions are composable grep '/home' /etc/passwd | wc -l

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functions are repeatable grep '/home' /etc/passwd | wc -l 23

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functions don’t have side-eﬀects a = "hello" a.capitalize! # a = “Hello" ! a = String.capitalize(a)

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functions don’t mutate state a = [3,2,1] a.reverse() // modifies a a.concat([4,5]) // new array ! a = Enum.reverse(a) a = Enum.concat(a, [4,5])

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“How do we program without GOTO?” Computer Science, 1968

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“How do we program without mutable state?” Computer Science, 2014

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immutability   allows re-using memory

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immutability   is the key to concurrency

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that’s great… ! so, uh, how do I   build something?

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Classes Instances behavior state

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Classes Instances behavior state Modules Processes

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Classes Instances behavior state Modules Processes you mean like, threads?

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processes are light elixir --erl "+P 1000000" \ -r chain.exs \ -e "Chain.run(400_000)" {5325361, "Result is 400000"} that’s 400k processes   spawning sequentially, running simultaneously in 5.3 seconds on a MacBook Air

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actors, not objects

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actors send & receive messages

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upon receiving a message, an actor may send a finite number of messages to other actors

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upon receiving a message, an actor may create a finite number of other new actors 

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upon receiving a message, an actor may designate the behavior to be used for the   next message

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but really   you don’t have to   think too much about it, thanks to OTP

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first, how to write sequential code  all over again

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know your type(s)

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base types Integers,   arbitrary precision Floats,  IEEE 754 64-bit Atoms, aka symbols Tuples, not arrays Lists, not arrays Binaries, not strings Functions Pids, Ports, References

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atoms :crypto the name is the value ! true, false, nil are atoms

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tuples {:arbitrary, items, [1,2]} any element accessible in constant time

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lists [:arbitrary, items, {1,2}] [:arbitrary|[items|[{1,2}]]] [head | tail] head accessible in constant time think of them like stacks

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implemented types Strings,   using binaries or   “character lists” Records,  using tuples Maps, aka dicts /   hashes / POJOs,   using Lists Streams, lazy-  loaded enums Regexs, Ranges, Sets

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ranges Enum.map(1..5, fn(i)-> i end) ! start, end can be any type enumeration requires integers

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records defrecord RgbColor, red: 0,   blue: 0, green: 0 ! like loosely typed Structs

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records RgbColor[red: 0.5,   blue: 100,   green: 'a7'] ! ! ! …really loose

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records new_color =  color.red(42) ! ! the only non-module type with functions

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functions adder = fn(a) -> fn (b) -> a + b end end can pass as values

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unnamed functions add2 = adder.(2) add2.(3) 5 remember original environment

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inline functions Enum.map([1,2],   &(&1 * &1)) save needless fn declarations

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composable inlines divrem = &{div(&1,&2), rem(&1,&2)} divrem.(13,5) # {2,3} lexer is pretty smart

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detachable len = &Enum.count/1 ! great for composing functions

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named functions defmodule Geometry do def area(item) do # math goes here end end

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many small functions ! area doesn’t have to branch by shape type

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pattern matching   assert, don’t assign

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LHS = RHS

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foo = 1 1 = foo ! these are assertions

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foo = 1 1 = foo 2 = foo ** (MatchError) no match of right hand side value: 1

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foo = 1 1 = foo ! identifiers on LHS are bound

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foo = 1 1 = foo ^foo = 2 ** (MatchError) no match of right hand side value: 2

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list = [1,4,9,16] [1,a|rest] = list 4 = a RHS compounds are destructured

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list = [1,4,9,16] [2,a|rest] = list ** (MatchError) no match   of right hand side value: [1,4,6,9]

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{Color, :rgb, {r,g,b}} = my_color ! destructuring can be used with any depth

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! {n,_} = Float.parse("1.618") ! ignore unwanted values   with underscores

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functions, reloaded

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! defmodule Color do def hex(:rgb, vals={r,g,b}) do # no conversion needed function signatures   perform pattern matching

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defmodule Factorial do def of(0), do: 1 def of(x), do: x * of(x-1) end declare multiple signatures instead of using if or case

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defmodule Factorial do def of(0), do: 1 def of(x) when is_number(x) and x > 0, do: x * of(x-1) end guard clauses   augment pattern matching

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Factorial.of(-100) ** (FunctionClauseError) no function clause matching in Factorial.of/1 guard clauses   are limited, but very useful

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defmodule Factorial do def of(x) when is_number(x) and x > 0, do: of(x, 1) defp of(0,a), do: a defp of(x,a), do: of(x-1, a*x) end tail-call optimization   doesn’t add to the stack

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! defmodule Color do def rgb(r\\0, g\\0, b\\0) do default values   match left-to-right save a ton of boilerplate

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home = &(Regex.match?(~{/home},&1)) ! blob = File.read!('/etc/passwd') lines = String.split(blob, "\n") matches = Enum.filter(lines, home) initial = Enum.take(matches, 5) users = Enum.map(initial, get_user) without mutation… lots of asserting?

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Enum.map( Enum.take( Enum.filter( String.split( File.read!( '/etc/passwd'), "\n"), home), 5), get_user) no… just… no

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functions are composable echo '/etc/passwd' | xargs -n 1 cat | grep '/home' | head -n 5 | cut -d: -f 1

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it’s easier to reason about small functions with no internal state

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imagine there’s   no if statement ! you couldn’t if you tried

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erlang doesn’t have if, but elixir does. it’s a macro.

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! if x < 3, do: IO.puts "hello", else: IO.puts "bye" and that’s how you use a macro  there’s also an unless macro

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but please don’t use else with unless

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if else? meet cond

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result = cond do whole(val,3) and whole(val,5) -> "FizzBuzz" whole(val, 3) -> "Fizz" whole(val, 5) -> "Buzz" true -> val end you probably just want function calls instead

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case or switch? we’ve got case ! hint: it uses pattern matching

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! case thing do c = Color[type=:rgb, {r,g,b}] when is_number(r) and r < 1 -> pattern matching with guards & destructuring

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unmatched cond clauses or case patterns will raise

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exceptions? ! they’re for when something unanticipated happens

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! case File.open("chain.exs") do { :ok, file } -> # something { :error, reason } -> # uh oh end this code anticipates a problem with file reading

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file = File.open!("chain.exs") this code doesn’t ! elixir convention:  ! functions raise on error

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let it crash ! don’t make ad-hoc decisions when something goes wrong

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do I actually know how I’m supposed to handle an error?

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concurrency through smart sequences

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actors are processes that talk and listen

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Classes Instances behavior state Modules Processes processes are cheap

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my god,   it’s full of processes 2001 by Stanley Kubrick

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! pid = spawn(ModuleName,  :function_name,  [arg1, arg2]) spawning new processes is easy

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! send(pid, [val1, val2]) sending messages is   fire & forget

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def function_name(arg1, arg2) do receive do :hello -> IO.puts("hello") val -> do_something(val) end end receiving messages is straightforward and uses pattern matching

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send(pid, {self, val1}) receive do response -> # handle ! def function_name(arg1, arg2) do receive do {p,v} -> send(p, process(v)) combine these   to wait for a response

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each process   has its own mailbox ! receive reads the first message

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def function_name(state) do receive do {p,v} -> send(p, process(v)) end function_name(new_state) end an actor   may designate the behavior   for the next message

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tail-call optimization means we aren’t   adding to the stack

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combine sending and receiving to parallelize

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Parallel.map( 1..n, &Factorial.of/1) ! ! elixir -r par.exs -e “Parallel.fac(5000)” 5000 items, last is 422… took 13547672 microseconds

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that was Factorial.of(n) for n in 1..5000 running simultaneously on all cores

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beam lets you connect multiple VMs ! (beyond our scope)

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the supervisor pattern is for managing processes

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defmodule GhostWhisper do def talk_to_dead do exit(99) # impossible something went wrong? crash

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{pid,ref} = Process.spawn_monitor( &GhostWhisper.talk_to_dead/0) receive do {:DOWN,^ref,:process,^pid,r} -> IO.puts(“#{inspect(pid)},#{r}”) monitoring tells you when  a process dies

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def dead_waiter do sleep 500; send(pid, "hi") ! spawn_link(GW,:dead_waiter,[self()]) receive do msg -> # never gets here after 100 -> exit(99) linking sets up process  dependencies

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extending with metaprogramming & monkeypatching ! (don’t worry, no actual monkeypatching)

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macros are metaprogramming done right

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homoiconicity the language has direct access to its own internal structures

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hygenic macros won’t clobber each others’ variables or those of the functions that use them ! you can turn hygiene oﬀ

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low-overhead macros modify the AST at compile time

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defmacro if(condition, body) do yes = Keyword.get(body, :do, nil) no = Keyword.get(body, :else, nil) quote do case unquote(condition) do false -> unquote(no) _ -> unquote(yes) quote writes to the output tree unquote writes variable content

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defmacro truthy(condition, body) do yes = Keyword.get(body, :do, nil) no = Keyword.get(body, :else, nil) quote do case unquote(condition) do val when val in [false, nil, 0, "", [], {}] -> unquote(no) _ -> unquote(yes) like javascript’s falsiness? here you go

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defmacro dynamic_def(name) do quote bind_quoted: [name: name] do def unquote(name)() do unquote(name) ! [:red, :green] |> Enum.each(&Unholy.dynamic_def(&1)) want to dynamically define   methods at compile time?   use a binding

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protocols are polymorphism for functions

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think of them as   type-specific decorators

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defimpl Enumerable, for: Bag do def count(collection) do # returns number of items in bag def member?(collection, value) # {:ok, boolean} def reduce(collection, acc, fun) # apply fun to the collection enables Enum to use Bag values

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implemented types like Sets, Streams, Ranges use the Enumerable protocol

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defimpl Access, for: Bag def access(container, key) # gets key from container ! my_bag[:thing] enables Bag variables   to use [] accessors

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Inspect is a protocol, if you want to pretty- print your own types

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behaviours are interface definitions for modules

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erlang has a british- english influence, so get used to the brit spelling

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defmodule My.Server do use GenServer.Behaviour @version 3 def init(initial) :: result def handle_call(request, from, state)   :: result def handle_cast(request, state)   :: result def handle_info(info, state) :: result def terminate(reason, state) def code_change(oldVsn, state, extra)  :: status OTP server interface definition

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declaring behaviour use and implelenting an interface lets you leverage powerful abstractions

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great tooling   makes a   foreign environment easier

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mix can throw down against rake, grunt, easy_install, npm, make, pip, & bundler

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create projects,   manage deps, test, & compile, generate docs

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documenation isn’t merely grafted on

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defmodule MyModule do @moduledoc """ ## This is my module “"" ! iex(1)> h(MyModule) MyModule ## This is my module

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@doc """ ignores its arg and returns 1 """ def function(_), do: 1 ! iex(2)> h(MyModule.function/1) def function(_) ignores its arg and returns 1

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# mix.exs defp deps do [ { :ex_doc, github:'elixir-lang/ex_doc'} ] end ! $ mix docs ExDoc makes HTML docs for you

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ExUnit leverages macros for the power of awesome

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defmodule MathTest do use ExUnit.Case ! test "math is correct" do assert( 2 + 2 = 5 ) end end test and assert are macros

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$ mix test Compiled lib/test/supervisor.ex Compiled lib/test.ex Generated test.app 1) test math is correct (MathTest) ** (ExUnit.ExpectationError) expected: 5 to match pattern (=): 2 + 2 at test/math_test.exs:5 assertion types are implied   by pattern matching & syntax tree

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the OTP sales pitch ! (sadly beyond our scope)

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libraries implementing best-practice patterns

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write your servers, state machines, event handlers & supervisors   to a common   abstract interface

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def current_state_name(:event_name, details) do # transition logic { :next_state, :new_state_name, details } end ! def new_state_name(:event_name, …) the state machine DSL is sexy

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leverage battle-tested patterns, tools for debugging, release management & more

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it’s still a young community,   but building on old infrastructure

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No content

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elixir-lang.org elixirsips.com Programming Elixir by Dave Thomas Elixir in Action by Saša Jurić

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erlang.org Programming Erlang by Joe Armstrong Learn You Some Erlang For Great Good by Frank Hébert learnyousomeerlang.com our meetup hosts, erlangsolutions.com

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thank you! ! Matthew Lyon twitter / github: mattly speakerdeck.com/mattly/intro-to-elixir ! typefaces: Source Sans Pro & Source Code Pro and ChunkFive