Spreading my love for Elixir and State Machines

1. Spreading myElixir Elixir love
3. This shit is easy
6. things can get things can get complex complex really fast really fast
7. State Machines State Machines
8. empty Shopping Cart Shopping Cart filled payed abandoned add item leave checkout
9. empty lock items add item in stock? no yes filled checkout leave payed? no payed yes abandoned unblock items
10. Models Models Controllers Controllers Views Views
11. Functional Functional Programming Programming
12. Functions must not Functions must not update values outside of it update values outside of it
13. Functions must not Functions must not depend on variables other depend on variables other than its parameters than its parameters
14. "Elixir".downcase # elixir
15. String.downcase("Elixir") # elixir
16. Machinery Machinery
17. defmodule YourProject.UserStateMachine do use Machinery, states: ["created", "partial", "complete"], transitions: %{ "created" => ["partial", "complete"], "partial" => "completed" } end
18. defmodule YourProject.UserStateMachine do use Machinery, states: ["created", "partial", "complete"], transitions: %{ "created" => ["partial", "complete"], "partial" => "completed" } end
19. defmodule YourProject.UserStateMachine do use Machinery, states: ["created", "partial", "complete"], transitions: %{ "created" => ["partial", "complete"], "partial" => "completed" } end
20. defmodule YourProject.UserStateMachine do use Machinery, states: ["created", "partial", "complete"], transitions: %{ "created" => ["partial", "complete"], "partial" => "completed" } end
21. defmodule YourProject.UserStateMachine do use Machinery, states: ["created", "partial", "complete"], transitions: %{ "created" => ["partial", "complete"], "partial" => "completed" } end
22. Machinery.transition_to(your_struct, UserStateMachine, "next_state") # {:ok, updated_struct}
23. Machinery.transition_to(your_struct, UserStateMachine, "next_state") # {:ok, updated_struct}
24. Machinery.transition_to(your_struct, UserStateMachine, "next_state") # {:ok, updated_struct}
25. Machinery.transition_to(your_struct, UserStateMachine, "next_state") # {:ok, updated_struct}
26. Guard Functions Guard Functions def guard_transition(struct, "complete") do Map.get(struct, :missing_fields) == false end
27. Guard Functions Guard Functions def guard_transition(struct, "complete") do Map.get(struct, :missing_fields) == false end
28. Guard Functions Guard Functions def guard_transition(struct, "complete") do Map.get(struct, :missing_fields) == false end def guard_transition(struct, "partial") do # ... end
29. Before and after callbacks Before and after callbacks def before_transition(struct, "complete"), do: struct def after_transition(struct, "complete"), do: struct
30. Shopping Cart Shopping Cart
31. defmodule FakeProject.ShoppingCartMachine do # We start by declaring all states and # each permitted transition. use Machinery, states: ["empty", "filled", "payed", "abandoned"], transitions: %{ "empty" => "filled", "filled" => ["payed", "abandoned"] } def guard_function(cart, "filled") do Item.has_stock?(cart.item) end def guard_function(cart, "payed") do Payment.status(cart) == :confirmed end def before_transition(cart, "filled") do Item.lock_form_cart(cart) cart end def after_transition(cart, "abadonned") do Item.unlock_form_cart(cart) cart end end
32. defmodule FakeProject.ShoppingCartMachine do # We start by declaring all states and # each permitted transition. use Machinery, states: ["empty", "filled", "payed", "abandoned"], transitions: %{ "empty" => "filled", "filled" => ["payed", "abandoned"] } def guard_function(cart, "filled") do Item.has_stock?(cart.item) end def guard_function(cart, "payed") do Payment.status(cart) == :confirmed end def before_transition(cart, "filled") do Item.lock_form_cart(cart) cart end def after_transition(cart, "abadonned") do Item.unlock_form_cart(cart) cart end end
33. defmodule FakeProject.ShoppingCartMachine do # We start by declaring all states and # each permitted transition. use Machinery, states: ["empty", "filled", "payed", "abandoned"], transitions: %{ "empty" => "filled", "filled" => ["payed", "abandoned"] } def guard_function(cart, "filled") do Item.has_stock?(cart.item) end def guard_function(cart, "payed") do Payment.status(cart) == :confirmed end def before_transition(cart, "filled") do Item.lock_form_cart(cart) cart end def after_transition(cart, "abadonned") do Item.unlock_form_cart(cart) cart end end
34. defmodule FakeProject.ShoppingCartMachine do # We start by declaring all states and # each permitted transition. use Machinery, states: ["empty", "filled", "payed", "abandoned"], transitions: %{ "empty" => "filled", "filled" => ["payed", "abandoned"] } def guard_function(cart, "filled") do Item.has_stock?(cart.item) end def guard_function(cart, "payed") do Payment.status(cart) == :confirmed end def before_transition(cart, "filled") do Item.lock_form_cart(cart) cart end def after_transition(cart, "abadonned") do Item.unlock_form_cart(cart) cart end end
35. defmodule FakeProject.ShoppingCartMachine do # We start by declaring all states and # each permitted transition. use Machinery, states: ["empty", "filled", "payed", "abandoned"], transitions: %{ "empty" => "filled", "filled" => ["payed", "abandoned"] } def guard_function(cart, "filled") do Item.has_stock?(cart.item) end def guard_function(cart, "payed") do Payment.status(cart) == :confirmed end def before_transition(cart, "filled") do Item.lock_form_cart(cart) cart end def after_transition(cart, "abadonned") do Item.unlock_form_cart(cart) cart end end
36. defmodule FakeProject.ShoppingCartMachine do # We start by declaring all states and # each permitted transition. use Machinery, states: ["empty", "filled", "payed", "abandoned"], transitions: %{ "empty" => "filled", "filled" => ["payed", "abandoned"] } def guard_function(cart, "filled") do Item.has_stock?(cart.item) end def guard_function(cart, "payed") do Payment.status(cart) == :confirmed end def before_transition(cart, "filled") do Item.lock_form_cart(cart) cart end def after_transition(cart, "abadonned") do Item.unlock_form_cart(cart) cart end end
37. defmodule FakeProject.ShoppingCartMachine do # We start by declaring all states and # each permitted transition. use Machinery, states: ["empty", "filled", "payed", "abandoned"], transitions: %{ "empty" => "filled", "filled" => ["payed", "abandoned"] } def guard_function(cart, "filled") do Item.has_stock?(cart.item) end def guard_function(cart, "payed") do Payment.status(cart) == :confirmed end def before_transition(cart, "filled") do Item.lock_form_cart(cart) cart end def after_transition(cart, "abadonned") do Item.unlock_form_cart(cart) cart end end
38. defmodule FakeProject.ShoppingCartMachine do # We start by declaring all states and # each permitted transition. use Machinery, states: ["empty", "filled", "payed", "abandoned"], transitions: %{ "empty" => "filled", "filled" => ["payed", "abandoned"] } def guard_function(cart, "filled") do Item.has_stock?(cart.item) end def guard_function(cart, "payed") do Payment.status(cart) == :confirmed end def before_transition(cart, "filled") do Item.lock_form_cart(cart) cart end def after_transition(cart, "abadonned") do Item.unlock_form_cart(cart) cart end end
39. BONUS BONUS
40. defmodule YourApp.Endpoint do # ... plug Machinery.Plug # ... end config :machinery, interface: true, repo: YourApp.Repo, model: YourApp.User, module: YourApp.UserStateMachine
43. state machines state machines are hard are hard
44. machinery machinery
45. things can get things can get complex complex really fast really fast
46. @joaomdmoura @joaomdmoura joaomdmoura.com