Elixir Elixir In 

How much? 

It depends 

What is “Elixir”? 

Basics + STDLIB 

of Elixir is written in Elixir 78% 

Compare to Ruby’s 44% 

Numbers? Meh 

if 

def 

|> 

Metaprogramming 

Code generation 

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“I’m speaking at ElixirConf!” 

“That’s nice. Where is it?” 

“Orlando.” 

“DISNEY IS THERE!!! CAN WE GO?!” 

“Ya, actually it’s at Disney.” 

“OMG!!! YOU’RE SPEAKING AT DISNEY?!!” 

“Haha, sort of” *interrupted* 

*on phone* “YA! He’s speaking at Disney!! We’re GOING!!!” *squeal* 

No content

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Metaprogramming 

No content

programming Meta 

Working on Data 

data quantities on which operations are performed — Dictionary.app 

4 + 2 data 

+(4, 2) data 

Kernel.+(4, 2) 

The program is data 

Macros 

Macros are everywhere 

good macros are invisible 

defmodule ItTest do use ExUnit.Case test “works” do assert It.works? end end macros 

Where is the data? Program 

defmodule ItTest do use ExUnit.Case test “works” do assert It.works? end end 

defmodule ItTest do use ExUnit.Case test “works” do assert It.works? end end 

defmodule ItTest do use ExUnit.Case test “works” do assert It.works? end end 

defmodule ItTest do use ExUnit.Case test “works” do assert It.works? end end 

Expression macro Expression ✨ ✨ 

Expression? 

“Quoted” Elixir code 

{func, …, args} 

Abstract Syntax Tree 

+ 1 - 2 3 

+ 1 - 2 3 ( ( )) func Args 

1 + ( 2 - 3 ) 

Args are quoted 

Expression.match?(:lol > :wat) # => false Expression.match?(:lol = :wat) # => true 

defmacro match?({:=, _, _}) do true end defmacro match?(_expr) do false end 

Expression.match?(:lol > :wat) # => false Expression.match?(:lol = :wat) # => true 

false # => false true # => true 

Must return quoted 

defmacro badmatch do {:=, [], [:lol, :wat]} end 

defmacro badmatch do quote do :lol = :wat end end 

Expression.badmatch # (MatchError) 

:lol = :wat # (MatchError) 

Quote 

{func, meta, args} 

{:=, [], [:lol, :wat]} 

quote do :lol = :wat end 

Sort of like strings… 

“1+1” 

quote(do: 1+1) 

quote do 1+1 end 

Return AST of Expression 

2 - 3 quote do end 

- 2 3 {: , […], [ , ]} (- 2 3) 

quote do 1 + (2 - 3) end 

{: , […], [ , {: , […], [ , ]}]} + 1 - 2 3 (+ 1 (- 2 3)) 

Easier to grok 

{:+, […], [1, {:-, […], [2, 3]}]} quote do 1 + (2 - 3) end 

Quoted Literals 

quote do: “foo” # “foo” quote do: :foo # :foo quote do: 1 # 1 quote do: [1] # [1] quote do: {1,2} # {1,2} quote do: [a: 1] # [a: 1] 

Unquote 

“Inject value in quote” 

Like string interpolation 

“Inject value into quoted string” 

name = “Sue” “hi name” # => “hi name” 

name = “Sue” “hi #{name}” # => “hi Sue” 

“Inject value into quoted Expression” 

num = 42 # => 42 quote do: 1 + num # => {:+, [], [1, {:num, [], :Elixir}]} 

num = 42 # => 42 quote do: 1 + unquote(num) # => {:+, [], [1, 42]} 

name = “Sue” “hi #{name}” # => “hi Sue” 

if 

if foo > 0 do IO.puts(“Pass!”) else IO.puts(“Fail.”) end 

if(…, do: …, else: …) 

if(…, [do: …, else: …]) cases cond 

Truthy & Falsey 

false || nil Falsey 

anything else Truthy 

case … do x when x in [false, nil] -> … _ -> … end cond cases 

defmacro if(c, do: tc, else: fc) do quote do case unquote(c) do x when x in [false, nil] -> unquote(fc) _ -> unquote(tc) end end end cond cases cond cases 

if do else end foo > 0 IO.puts(“Pass!”) IO.puts(“Fail.”) 

case do x when x in [false, nil] -> _ -> end foo > 0 IO.puts(“Fail.”) IO.puts(“Pass!”) 

When to macro… 

#1 Don’t 

Write functions 

defmacro add(a, b) do quote do unquote(a) + unquote(b) end end 

def add(a, b) do a + b end 

More direct 

Less error-prone 

#2 Constants 

defmacro seconds_per_minute, do: 60 defmacro minutes_per_hour, do: 60 

#3 DSL 

html do body do div class: “content” do p “Engaging content.” end end end 

#4 Hide details 

test “works” do assert It.works? end 

#5 Reduce boilerplate 

Language extension 

defmodule Lolwat do def lol do :wat end end 

:elixir_module.compile(Lolwat, {:def, [context: Elixir, import: Kernel], [{:lol, [context: Elixir], Elixir}, [do: :wat]]}, [], __ENV__) 

:elixir_module.compile(Lolwat, {:def, [context: Elixir, import: Kernel], [{:lol, [context: Elixir], Elixir}, [do: :wat]]}, [], %{__struct__: Macro.Env, aliases: [], context: nil, context_modules: [Mex], export_vars: nil, file: "iex", function: nil, functions: [Mex: [expand_all: 2], "IEx.Helpers": [c: 1, c: 2, cd: 1, clear: 0, flush: 0, h: 0, i: 1, l: 1, ls: 0, ls: 1, nl: 1, nl: 2, pid: 1, pid: 3, pwd: 0, r: 1, recompile: 0, respawn: 0, v: 0, v: 1], Kernel: [!=: 2, !==: 2, *: 2, +: 1, +: 2, ++: 2, -: 1, -: 2, --: 2, /: 2, <: 2, <=: 2, ==: 2, ===: 2, =~: 2, >: 2, >=: 2, abs: 1, apply: 2, apply: 3, binary_part: 3, bit_size: 1, byte_size: 1, div: 2, elem: 2, exit: 1, function_exported?: 3, get_and_update_in: 3, get_in: 2, hd: 1, inspect: 1, inspect: 2, is_atom: 1, is_binary: 1, is_bitstring: 1, is_boolean: 1, is_float: 1, is_function: 1, is_function: 2, is_integer: 1, is_list: 1, is_map: 1, is_number: 1, is_pid: 1, is_port: 1, is_reference: 1, is_tuple: 1, length: 1, macro_exported?: 3, make_ref: 0, map_size: 1, max: 2, min: 2, node: 0, node: 1, not: 1, pop_in: 2, put_elem: 3, put_in: 3, rem: 2, round: 1, self: 0, send: 2, spawn: 1, spawn: 3, spawn_link: 1, spawn_link: 3, spawn_monitor: 1, spawn_monitor: 3, struct: 1, struct: 2, struct!: 1, struct!: 2, throw: 1, tl: 1, trunc: 1, tuple_size: 1, update_in: 3]], lexical_tracker: nil, line: 2, macro_aliases: [], macros: [Mex: [mex: 1], "IEx.Helpers": [b: 1, h: 1, import_file: 1, import_file: 2, import_file_if_available: 1, import_if_available: 1, import_if_available: 2, s: 1, t: 1], Kernel: [!: 1, &&: 2, ..: 2, <>: 2, @: 1, alias!: 1, and: 2, binding: 0, binding: 1, def: 1, def: 2, defdelegate: 2, defexception: 1, defimpl: 2, defimpl: 3, defmacro: 1, defmacro: 2, defmacrop: 1, defmacrop: 2, defmodule: 2, defoverridable: 1, defp: 1, defp: 2, defprotocol: 2, defstruct: 1, destructure: 2, get_and_update_in: 2, if: 2, in: 2, is_nil: 1, match?: 2, or: 2, pop_in: 1, put_in: 2, raise: 1, raise: 2, reraise: 2, reraise: 3, sigil_C: 2, sigil_D: 2, sigil_N: 2, sigil_R: 2, sigil_S: 2, sigil_T: 2, sigil_W: 2, sigil_c: 2, sigil_r: 2, sigil_s: 2, sigil_w: 2, to_char_list: 1, to_charlist: 1, to_string: 1, unless: 2, update_in: 2, use: 1, use: 2, var!: 1, var!: 2, |>: 2, ||: 2]], module: nil, requires: [IEx.Helpers, Kernel, Kernel.Typespec, Mex], vars: []}) 

good macros are invisible 

CJUMZ&MJYJS.FUB 

!JBNWFSZ Questions?