Day in the Life of a Functional Programmer

Transcript

1. A Day in the Life of a Func onal Programmer Richard Dallaway
2. Modern Development Func onal Programming with Types
3. Why now?
4. Why now? Modern compilers have powerful type system
5. A Day in the Life
6. Func onal Programming Is For Everyone Makes Change Easier
7. The Morning Standup
8. CRM RDBMS REST Server
9. $ http GET :8080/customers HTTP/1.1 200 OK Content-Type: application/json [ { "id": 1, "name": "Alice", "phone": "+1 555 1234" }, { "id": 2, "name": "Bob", "phone": "+1 555 5678" } ]
10. As a customer, I should have a subscrip on, so I can receive the company magazine.
11. No subscrip on Ac ve subscrip on Lapsed subscrip on
12. Algebraic Data Types Structural Recusion Unfamiliar names for simple powerful ideas
13. sealed trait Subscription
14. sealed trait Subscription case object Never extends Subscription case object Active extends Subscription case object Lapsed extends Subscription
15. sealed trait Subscription case object Never extends Subscription case class Active(expires: Date) extends Subscription case object Lapsed extends Subscription
16. sealed trait Subscription case object Never extends Subscription case class Active(expires: Date) extends Subscription case object Lapsed extends Subscription case class Customer( name : String, phone : String, sub : Subscription )
17. sealed trait Subscription case object Never extends Subscription case class Active(expires: Date) extends Subscription case object Lapsed extends Subscription case class Customer( name : String, phone : String, sub : Subscription ) def transition(sub: Subscription, at: Date): Subscription = ???
18. sealed trait Subscription case object Never extends Subscription case class Active(expires: Date) extends Subscription case object Lapsed extends Subscription case class Customer( name : String, phone : String, sub : Subscription ) def transition(sub: Subscription, at: Date): Subscription = sub match { case Lapsed | Never => sub case Active(exp) => ??? }
19. sealed trait Subscription case object Never extends Subscription case class Active(expires: Date) extends Subscription case object Lapsed extends Subscription case class Customer( name : String, phone : String, sub : Subscription ) def transition(sub: Subscription, at: Date): Subscription = sub match { case Lapsed | Never => sub case Active(exp) => if (at > exp) Lapsed else sub }
20. “Marke ng just reminded me we give free subscrip ons to some customers” — Product Owner
21. sealed trait Subscription case object Never extends Subscription case class Active(expires: Date) extends Subscription case object Lapsed extends Subscription
22. sealed trait Subscription case object Never extends Subscription case class Active(expires: Date) extends Subscription case object Lapsed extends Subscription case object Freebie extends Subscription def transition(sub: Subscription, at: Date): Subscription = sub match { case Lapsed | Never => sub case Active(exp) => if (at > exp) Lapsed else sub } ERROR: non‐exhaus ve match
23. Move side effects out
24. def transition(c: Customer, at: Date): Action = ???
25. def transition(c: Customer, at: Date): Action = ??? sealed trait Action case object NoAction extends Action case class EncourageRenewal(c: Customer) extends Action case class Expire(c: Customer) extends Action ...
26. def transition(c: Customer, at: Date): Action = ??? sealed trait Action case object NoAction extends Action case class EncourageRenewal(c: Customer) extends Action case class Expire(c: Customer) extends Action ... def perform(a: Action): Unit = a match { case NoAction => case Expire(c) => sendSMS(c.phone) ...etc }
27. ADTs Safe Versi le Separate data & behaviour
28. Output JSON to the Client { "id": 1, "name": "Alice", "phone": "+1 555 1234", "sub": { "type": "expired" } }
29. Type Class Big things from ny building blocks
30. Turn Data into JSON text 7.toString
31. Turn Data into JSON text 7.toString 7 "\"" + "Hello" + "\"" "Hello"
32. Turn Data into JSON text 7.toString 7 "\"" + "Hello" + "\"" "Hello" { greeting: "Hello", count: 7 }
33. Turn Data into JSON text 7.toString 7 "\"" + "Hello" + "\"" "Hello" { greeting: "Hello", count: 7 } Int => String String => String
34. Turn Data into JSON text 7.toString 7 "\"" + "Hello" + "\"" "Hello" { greeting: "Hello", count: 7 } Int => String String => String T => String
35. trait JsonFormat[T] { def format(value: T): String }
36. trait JsonFormat[T] { def format(value: T): String } val intFormat = new JsonFormat[Int] { def format(value: Int): String = value.toString } val strFormat = new JsonFormat[String] { def format(value: String): String = "\"" + value + "\"" }
37. trait JsonFormat[T] { def format(value: T): String } val intFormat = new JsonFormat[Int] { def format(value: Int): String = value.toString } val strFormat = new JsonFormat[String] { def format(value: String): String = "\"" + value + "\"" } def outputJson[T](value: T)(jf: JsonFormat[T]) = jf.format(value) outputJson(7)(intFormat) // 7
38. trait JsonFormat[T] { def format(value: T): String } implicit val intFormat = new JsonFormat[Int] { def format(value: Int): String = value.toString } implicit val strFormat = new JsonFormat[String] { def format(value: String): String = "\"" + value + "\"" } def outputJson[T](value: T)(implicit jf: JsonFormat[T]) = jf.format(value) outputJson(7) // 7
39. [ "Hello", "there" ] [ 1, 2, 3, 4 ] [ [1,2], [3,4] ]
40. implicit def listFormat[T] = new JsonFormat[List[T]] { def format(values: List[T]): String = { ??? } }
41. implicit def listFormat[T] = new JsonFormat[List[T]] { def format(values: List[T]): String = { val formattedValues = { ??? } "[" + formattedValues.mkString(",") + "]" } }
42. implicit def listFormat[T] = new JsonFormat[List[T]] { def format(values: List[T]): String = { val formattedValues = for { v <- values } yield ??? "[" + formattedValues.mkString(",") + "]" } }
43. implicit def listFormat[T](implicit jf: JsonFormat[T]) = new JsonFormat[List[T]] { def format(values: List[T]): String = { val formattedValues = for { v <- values } yield jf.format(v) "[" + formattedValues.mkString(",") + "]" } }
44. implicit def listFormat[T](implicit jf: JsonFormat[T]) = new JsonFormat[List[T]] { def format(values: List[T]): String = { val formattedValues = for { v <- values } yield jf.format(v) "[" + formattedValues.mkString(",") + "]" } } def outputJson[T](value: T)(implicit jf: JsonFormat[T]) = jf.format(value) outputJson( List(1,2,3,4) ) [1,2,3,4]
45. implicit def listFormat[T](implicit jf: JsonFormat[T]) = new JsonFormat[List[T]] { def format(values: List[T]): String = { val formattedValues = for { v <- values } yield jf.format(v) "[" + formattedValues.mkString(",") + "]" } } def outputJson[T](value: T)(implicit jf: JsonFormat[T]) = jf.format(value) outputJson( List(1,2,3,4) ) [1,2,3,4] outputJson( List( List(1,2), List(3,4) ) ) [ [1,2], [3,4] ]
46. Type Class Small Building Blocks Combined by the Compiler Used Everywhere
47. case class Customer( name : String, phone : String, id : Long ) sql" select name, phone, id from customer ".query[Customer]
48. case class Customer( name : String, phone : String, id : Long ) sql" select name, phone, id from customer ".query[Customer] implicit val SubscriptionMeta: Meta[Subscription] = Meta[String].nxmap(ch => ch match { case "A" => Active case "L" => Lapsed case "N" => Never }, sub => sub match { case Active => "A" case Lapsed => "L" case Never => "N" })
49. Used Everywhere ADTs Type Classes
50. As a customer, I should have an control over my details, so I can update some or all of them.
51. class CustomerAPI(db: Database) { val service = HttpService { case GET -> Root / "customers" => Ok(db.list) case GET -> Root / "customers" / IntVar(id) => db.find(id).flatMap { case Some(customer) => Ok(customer) case None => NotFound() } } }
52. class CustomerAPI(db: Database) { val service = HttpService { case GET -> Root / "customers" => Ok(db.list) case GET -> Root / "customers" / IntVar(id) => db.find(id).flatMap { case Some(customer) => Ok(customer) case None => NotFound() } case PATCH -> Root / "customers" / IntVar(id) => decode the patch lookup the customer in the database found a record? somehow apply the patch to the record update the database otherwise, 404 the request } }
53. Simplified Patch { "name" : "Robert" } or { "name" : "Robert", "phone : "+1 555 555" }
54. Simplified Patch (Customer, Patch) => Customer
55. case class Customer( id : Long, name : String, phone : String ) case class CustomerPatch( name : Option[String], phone : Option[String] )
56. case class Customer( id : Long, name : String, phone : String ) case class CustomerPatch( name : Option[String], phone : Option[String] ) trait Merge[Into, From] { def merge(i: Into, f: From): Into } def merge[Into, From](i: Into, f: From) = ???
57. case class Customer( id : Long, name : String, phone : String ) case class CustomerPatch( name : Option[String], phone : Option[String] ) trait Merge[Into, From] { def merge(i: Into, f: From): Into } def merge[Into, From](i: Into, f: From) (implicit m: Merge[Into, From]) = m.merge(i, f)
58. case class Customer( id : Long, name : String, phone : String ) case class CustomerPatch( name : Option[String], phone : Option[String] ) trait Merge[Into, From] { def merge(i: Into, f: From): Into } def merge[Into, From](i: Into, f: From) (implicit m: Merge[Into, From]) = m.merge(i, f) implicit def customerMerge: Merge[Customer, CustomerPatch] = ???
59. case class Customer( id : Long, name : String, phone : String ) case class CustomerPatch( name : Option[String], phone : Option[String] ) trait Merge[Into, From] { def merge(i: Into, f: From): Into } def merge[Into, From](i: Into, f: From) (implicit m: Merge[Into, From]) = m.merge(i, f) implicit def customerMerge: Merge[Customer, CustomerPatch] = ??? implicit def optMerge = new Merge[String, Option[String]] { def merge(initial: String, update: Option[String]) = update match { case Some(value) => value case None => initial } }
60. case class Customer( id : Long, name : String, phone : String ) case class CustomerPatch( name : Option[String], phone : Option[String] ) trait Merge[Into, From] { def merge(i: Into, f: From): Into } def merge[Into, From](i: Into, f: From) (implicit m: Merge[Into, From]) = m.merge(i, f) implicit def customerMerge: Merge[Customer, CustomerPatch] = ??? merge( Customer(1, "Bob", "555-123"), CustomerPatch(Some("Robert"), None) ) Customer(1, "Robert", "555-123")
61. Pu ng it all together... case req @ PATCH -> Root / "customers" / IntVar(id) => req.decode[CustomerPatch] { patch => db.find(id).flatMap { case None => NotFound() case Some(customer) => val updated = merge(customer, patch) Ok(db.update(updated)) } } val merge = bulletin.AutoMerge[Customer, CustomerPatch] case class CustomerPatch( name : Option[String], phone : Option[String] )
62. ADTs Safe, Versi le Type Classes Combining Small Building Blocks
63. Scala Modern Powerful Compiler Func onal Programming JVM, Scala Na ve, Scala.js
64. Help Make Change Easier
65. Thank You h ps:/ /underscore.io/