FUN WITH MACROSNadav Wiener

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

sealed trait Suspectcase object MissScarlet extends Suspectcase object ColonelMustard extends Suspectcase object MrsWhite extends Suspectcase object ReverendGreen extends Suspectcase object MrsPeacock extends Suspectcase object ProfessorPlum extends Suspect

The Suspects

The Weapons

sealed trait Weaponcase object Candlestick extends Weaponcase object Dagger extends Weaponcase object LeadPipe extends Weaponcase object Revolver extends Weaponcase object Rope extends Weaponcase object Wrench extends Weapon

The Rooms

sealed trait Roomcase object Kitchen extends Roomcase object Ballroom extends Roomcase object Conservatory extends Roomcase object DiningRoom extends Roomcase object BilliardRoom extends Roomcase object Library extends Roomcase object Lounge extends Roomcase object Hall extends Roomcase object Study extends Room

The Accusation

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

BUT NOW WHAT?

Simple answer:val accusation = Accusation( ColonelMustard, Library, LeadPipe)

or build a fancy API

Mixfix notation ⇒ fancy

Example

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

@syntax def _inThe_withThe_

(ColonelMustard inThe Library withThe LeadPipe)

Why the awkward name?

@syntax def _inThe_withThe_

(ColonelMustard inThe Library withThe LeadPipe)

the method name is parsed by the macro

MACROS FORMULA1

INTRO

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") }}

println(Cowsay.cowsay("use macros!"))

_______________ < 'use macros!' > --------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || ||

_______________ < 'use macros!' > --------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || ||

_______________ < 'use macros!' > --------------- \ ^__^ \ (oo)\_______ (__)\ )\/\ ||----w | || ||

Compiled code keeps working even after removing ‘cowsay’

TYPE PROVIDERS I:MACRO

ANNOTATIONS

Available in 2.10 Macro Paradise

Macro applied using @syntax

class syntax extends StaticAnnotation { def macroTransform(annottees: Any*) = macro Mixfix.impl}

Implemented like other macros

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

Enables adding new types and definitions

@syntax def _inThe_withThe_(…) = //…

import _inThe_withThe_._!

TYPE PROVIDERS II: SYNTHETIC

STRUCTURAL TYPES

val foo = new { def bar() = println(3)} !foo.bar()!

Structural type:

Type checked

Use reflection at runtime

Can be generated using 2.10 def macros

Structural types:

ADJECTIVES WITH MACROS

The challenge

Book(true, short, red)

Getting from:

To:

case class Book( interesting: Boolean = false, length: Length = short, color: Color = red)

an (interesting, long, red) Book

mkAdjectives extracts adjectives

Literate initialization for finite fields: boolean, enumeration, case objects

Inspired by E

object Book { val adjectives = Adjectives.mkAdjectives[Book]}import Book.adjectives._!println(an (interesting, long, red) Book)!

THANK YOU

Macro Paradisehttp://docs.scala-lang.org/overviews/macros/paradise.htmlScala Adjectiveshttps://github.com/hunam/scala-adjectivesScala Mixfixhttps://github.com/hunam/scala-mixfix

WE’RE HIRING contact nadav@lynxguard.com