A short talk about using type providers for fun and profit. (well, mostly fun). The talk was delivered at Underscore, the Israeli Scala user group. Video: http://parleys.com/play/530e2217e4b06b7f61f3fc06 1) Mixfix notation: going from @syntax def _inThe_withThe_(...) = ... to (ColonelMustard inThe LoungeRoom withThe LeadPipe) GitHub: https://github.com/hunam/scala-mixfix 2) Use adjectives to describe your objects: going from Book(length = long, interesting = true, color = red) to a (long, interesting, red) Book GitHub: https://github.com/hunam/scala-adjectives

1. FUN WITH MACROS
Nadav Wiener

3. It was Colonel Mustard, in the
lounge room, with a rope

4. The Suspects
sealed trait Suspect
case object MissScarlet extends Suspect
case object ColonelMustard extends Suspect
case object MrsWhite extends Suspect
case object ReverendGreen extends Suspect
case object MrsPeacock extends Suspect
case object ProfessorPlum extends Suspect

5. sealed trait Weapon
case object Candlestick extends Weapon
case object Dagger extends Weapon
case object LeadPipe extends Weapon
case object Revolver extends Weapon
case object Rope extends Weapon
case object Wrench extends Weapon
The
Weapons

6. The Rooms
sealed trait Room
case object Kitchen extends Room
case object Ballroom extends Room
case object Conservatory extends Room
case object DiningRoom extends Room
case object BilliardRoom extends Room
case object Library extends Room
case object Lounge extends Room
case object Hall extends Room
case object Study extends Room

7. case class Accusation(
suspect: Suspect,
room: Room,
weapon: Weapon)
The
Accusation

8. BUT NOW
WHAT?

9. Simple answer:
val accusation = Accusation(
ColonelMustard, Library, LeadPipe)
or build a fancy API

10. Mixfix notation
fancy

11. Example

12. @syntax def _inThe_withThe_
_inThe_withThe_
(suspect: Suspect, room: Room, weapon: Weapon) =
Accusation(suspect, room, weapon)
!
import _inThe_withThe_._
!
!
(ColonelMustard inThe Library withThe LeadPipe) ==
accusation
Why the awkward name?

13. @syntax def _inThe_withThe_
(ColonelMustard inThe Library withThe LeadPipe)
the method name is
parsed by the macro

14. MACROS
FORMULA1
INTRO

15. object Cowsay {
def cowsay(text: String): String = macro cowsayImpl
!
def cowsayImpl(c: Context)
(text: c.Expr[String]):
c.Expr[String] = {
!
import c.universe._
import sys.process._
!
val Literal(Constant(input)) = text.tree
val output = s"cowsay '$input'"!!
c.Expr(q"$output")
}
}

16. println(Cowsay.cowsay("use macros!"))
_______________
< 'use macros!' >
--------------
^__^
(oo)_______
(__)
)/
||----w |
||
||

17. Compiled code keeps working
even after removing ‘cowsay’
_______________
< 'use macros!' >
--------------
^__^
(oo)_______
(__)
)/
||----w |
||
||

18. Available in 2.10
Macro Paradise
TYPE PROVIDERS I:
MACRO
ANNOTATIONS

19. class syntax extends StaticAnnotation {
def macroTransform(annottees: Any*) =
macro Mixfix.impl
}
Macro applied using @syntax

20. object Mixfix {
def impl(c: Context)
(annottees: c.Expr[Any]*): c.Expr[Any] = //…
}
Implemented like other macros

21. @syntax def _inThe_withThe_(…) = //…
import _inThe_withThe_._
!
Enables adding new types
and definitions

22. TYPE PROVIDERS II:
SYNTHETIC
STRUCTURAL TYPES

23. Structural type:
val foo = new {
def bar() = println(3)
}
!
foo.bar()
!

24. Structural types:
Type checked
Use reflection at runtime
Can be generated using 2.10 def
macros

25. ADJECTIVES WITH MACROS

26. The challenge
Getting from:
case class Book(
interesting: Boolean = false,
length: Length = short,
color: Color = red)
Book(true, short, red)
To:
an (interesting, long, red) Book

27. mkAdjectives extracts adjectives
object Book {
val adjectives = Adjectives.mkAdjectives[Book]
}
import Book.adjectives._
!
println(an (interesting, long, red) Book)
!
Literate initialization for finite fields:
boolean, enumeration, case objects
Inspired by E

28. THANK YOU

29. WE’RE HIRING
contact nadav@lynxguard.com
Macro Paradise
http://docs.scala-lang.org/overviews/macros/paradise.html
Scala Adjectives
https://github.com/hunam/scala-adjectives
Scala Mixfix
https://github.com/hunam/scala-mixfix