AUXify

mvnrepository repo1.maven

Contents

• Using AUXify-Shapeless
• Using AUXify-Macros
  • @aux (helper for type refinement)
  • @self
  • @instance (constructor)
  • @apply (materializer)
  • @delegated
  • @syntax
  • @poly
• Using AUXify-Meta
  • Code generation with Scalafix
  • Rewriting with Scalafix
  • Code generation with Scalameta

Using AUXify-Shapeless

Write in build.sbt

scalaVersion := "2.13.3"
//scalaVersion := "2.12.11"
//scalaVersion := "2.11.12"
//scalaVersion := "2.10.7"

resolvers += Resolver.sonatypeRepo("public")

libraryDependencies ++= Seq(
  "com.github.dmytromitin" %% "auxify-shapeless" % [LATEST VERSION],
  "com.github.dmytromitin" %% "shapeless" % (CrossVersion.partialVersion(scalaVersion.value) match {
    case Some((2, v)) if v >= 11 => "2.4.0-M1-30032020-e6c3f71-PATCH"
    case _                       => "2.4.0-SNAPSHOT-18022020-bf55524-PATCH"
  })
)

Helps to overcome Shapeless limitation that shapeless.LabelledGeneric is Symbol-based rather than String-based.

Introduces type classes SymbolToString, StringToSymbol to convert between symbol singleton type and string singleton type

implicitly[StringToSymbol.Aux["a", Symbol @@ "a"]]
implicitly[SymbolToString.Aux[Symbol @@ "a", "a"]]
stringToSymbol("a") // returns Symbol("a") of type Symbol @@ "a"
symbolToString(Symbol("a")) // returns "a" of type "a"

and String-based type class com.github.dmytromitin.auxify.shapeless.LabelledGeneric

case class A(i: Int, s: String, b: Boolean)
implicitly[LabelledGeneric.Aux[A, Record.`"i" -> Int, "s" -> String, "b" -> Boolean`.T]]
LabelledGeneric[A].to(A(1, "a", true)) // field["i"](1) :: field["s"]("a") :: field["b"](true) :: HNil
LabelledGeneric[A].from(field["i"](1) :: field["s"]("a") :: field["b"](true) :: HNil) // A(1, "a", true)

Also there are convenient syntaxes

import com.github.dmytromitin.auxify.shapeless.hlist._
import StringsToSymbols.syntax._
("a".narrow :: "b".narrow :: "c".narrow :: HNil).stringsToSymbols // 'a.narrow :: 'b.narrow :: 'c.narrow :: HNil
import SymbolsToStrings.syntax._
('a.narrow :: 'b.narrow :: 'c.narrow :: HNil).symbolsToStrings // "a".narrow :: "b".narrow :: "c".narrow :: HNil

import com.github.dmytromitin.auxify.shapeless.coproduct._
import StringsToSymbols.syntax._
(Inr(Inr(Inl("c".narrow))) : "a" :+: "b" :+: "c" :+: CNil).stringsToSymbols // Inr(Inr(Inl('c.narrow))) : (Symbol @@ "a") :+: (Symbol @@ "b") :+: (Symbol @@ "c") :+: CNil
import SymbolsToStrings.syntax._
(Inr(Inr(Inl('c.narrow))) : (Symbol @@ "a") :+: (Symbol @@ "b") :+: (Symbol @@ "c") :+: CNil).symbolsToStrings // Inr(Inr(Inl("c".narrow))) : "a" :+: "b" :+: "c" :+: CNil

import com.github.dmytromitin.auxify.shapeless.record._
import StringsToSymbols.syntax._
(field["a"](1) :: field["b"]("s") :: field["c"](true) :: HNil).stringsToSymbols // field[Symbol @@ "a"](1) :: field[Symbol @@ "b"]("s") :: field[Symbol @@ "c"](true) :: HNil
import SymbolsToStrings.syntax._
(field[Symbol @@ "a"](1) :: field[Symbol @@ "b"]("s") :: field[Symbol @@ "c"](true) :: HNil).symbolsToStrings // field["a"](1) :: field["b"]("s") :: field["c"](true) :: HNil

import com.github.dmytromitin.auxify.shapeless.union._
import StringsToSymbols.syntax._
(Inr(Inr(Inl(field["c"](true)))): Union.`"a" -> Int, "b" -> String, "c" -> Boolean`.T).stringsToSymbols // Inr(Inr(Inl(field[Witness.`'c`.T](true)))): Union.`'a -> Int, 'b -> String, 'c -> Boolean`.T
import SymbolsToStrings.syntax._
(Inr(Inr(Inl(field[Symbol @@ "c"](true)))): Union.`'a -> Int, 'b -> String, 'c -> Boolean`.T).symbolsToStrings // Inr(Inr(Inl(field[Witness.`"c"`.T](true)))): Union.`"a" -> Int, "b" -> String, "c" -> Boolean`.T

You can play with AUXify online at Scastie: https://scastie.scala-lang.org/r52fCgloRc2VVM5FnNmbsQ

Using AUXify-Macros

Write in build.sbt

scalaVersion := "2.13.3"
//scalaVersion := "2.12.11"
//scalaVersion := "2.11.12"
//scalaVersion := "2.10.7"

resolvers += Resolver.sonatypeRepo("public")

libraryDependencies += "com.github.dmytromitin" %% "auxify-macros" % [LATEST VERSION]

scalacOptions += "-Ymacro-annotations" // in Scala >= 2.13
//addCompilerPlugin("org.scalamacros" % "paradise" % "2.1.1" cross CrossVersion.full) // in Scala <= 2.12

@aux (helper for type refinement)

Transforms

@aux
trait Add[N <: Nat, M <: Nat] {
  type Out <: Nat
  def apply(n: N, m: M): Out
}

into

trait Add[N <: Nat, M <: Nat] {
  type Out <: Nat
  def apply(n: N, m: M): Out
}

object Add {
  type Aux[N <: Nat, M <: Nat, Out0 <: Nat] = Add[N, M] { type Out = Out0 }
}

So it can be used:

implicitly[Add.Aux[_2, _3, _5]]

Convenient for type-level programming.

@self

Transforms

@self
sealed trait Nat {
  type ++ = Succ[Self]
}

@self
case object _0 extends Nat 

type _0 = _0.type

@self
case class Succ[N <: Nat](n: N) extends Nat

into

sealed trait Nat { self =>
  type Self >: self.type <: Nat { type Self = self.Self }
  type ++ = Succ[Self]
}

case object _0 extends Nat {
  override type Self = _0
}

type _0 = _0.type

case class Succ[N <: Nat](n: N) extends Nat {
  override type Self = Succ[N]
}

Convenient for type-level programming.

Generating lower bound >: self.type and/or F-bound type Self = self.Self for trait can be switched off

@self(lowerBound = false, fBound = false)

@instance (constructor)

Transforms

@instance
trait Monoid[A] {
  def empty: A
  def combine(a: A, a1: A): A
}

into

trait Monoid[A] {
  def empty: A
  def combine(a: A, a1: A): A
}

object Monoid {
  def instance[A](f: => A, f1: (A, A) => A): Monoid[A] = new Monoid[A] {
    override def empty: A = f
    override def combine(a: A, a1: A): A = f1(a, a1)
  }
}

So it can be used

implicit val intMonoid: Monoid[Int] = instance(0, _ + _)

Polymorphic methods are not supported (since Scala 2 lacks polymorphic functions).

@apply (materializer)

Transforms

@apply
trait Show[A] {
  def show(a: A): String
}

into

trait Show[A] {
  def show(a: A): String
}

object Show {
  def apply[A](implicit inst: Show[A]): Show[A] = inst
}

So it can be used

Show[Int].show(10)

Method materializing type class can return more precise type than the one of implicit to be found (like the in Shapeless or summon in Dotty). For example

@apply
trait Add[N <: Nat, M <: Nat] {
  type Out <: Nat
  def apply(n: N, m: M): Out
}

is transformed into

trait Add[N <: Nat, M <: Nat] {
  type Out <: Nat
  def apply(n: N, m: M): Out
}

object Add {
  def apply[N <: Nat, M <: Nat](implicit inst: Add[N, M]): Add[N, M] { type Out = inst.Out } = inst
}

Simulacrum annotation @typeclass also generates, among other, materializer but doesn't support type classes with multiple type parameters.

@delegated

Generates methods in companion object delegating to implicit instance of trait (type class).

Transforms

@delegated
trait Show[A] {
  def show(a: A): String
}

into

trait Show[A] {
  def show(a: A): String
}

object Show {
  def show[A](a: A)(implicit inst: Show[A]): String = inst.show(a)
}

So it can be used

Show.show(10)

@syntax

Transforms

@syntax
trait Monoid[A] {
  def empty: A
  def combine(a: A, a1: A): A
}

into

trait Monoid[A] {
  def empty: A
  def combine(a: A, a1: A): A
}

object Monoid {
  object syntax {
    implicit class Ops[A](a: A) {
      def combine(a1: A)(implicit inst: Monoid[A]): A = inst.combine(a, a1)
    }
  }
}

So it can be used

import Monoid.syntax._
2 combine 3

Simulacrum annotation @typeclass also generates syntax but doesn't support type classes with multiple type parameters.

Inheritance of type classes is not supported (anyway it's broken).

@poly

Transforms

@poly
trait Add[N <: Nat, M <: Nat] {
  type Out <: Nat
  def apply(n: N, m: M): Out
}

into

trait Add[N <: Nat, M <: Nat] {
  type Out <: Nat
  def apply(n: N, m: M): Out
}

object Add {
  object addPoly extends Poly2 {
    implicit def cse[N <: Nat, M <: Nat](implicit add: Add[N, M]): Case.Aux[N, M, add.Out] = at((n, m) => add(n, m)) 
  }
}

@poly is not implemented yet. See issue.

Using AUXify-Meta

Currently only @aux is implemented as Scalafix rewriting rule. It's a semantic rule since we need companion object.

Meta annotation @aux works only with classes on contrary to macro annotation @aux working only with traits. This will be fixed.

Code generation with Scalafix

For code generation with Scalameta + SemanticDB + Scalafix write in project/plugins.sbt

addSbtPlugin("ch.epfl.scala" % "sbt-scalafix" % "0.9.18")

and in build.sbt

import com.geirsson.coursiersmall.{Repository => R}

lazy val V = _root_.scalafix.sbt.BuildInfo

inThisBuild(Seq(
  scalaVersion := V.scala213,
  addCompilerPlugin(scalafixSemanticdb),
  scalafixResolvers in ThisBuild += new R.Maven("https://oss.sonatype.org/content/groups/public/"),
  // brings rewriting rules
  scalafixDependencies in ThisBuild += "com.github.dmytromitin" %% "auxify-meta" % [LATEST VERSION],
  scalacOptions += "-Yrangepos" // for SemanticDB
))

lazy val in = project
  .settings(
    // brings meta annotations
    libraryDependencies += "com.github.dmytromitin" %% "auxify-meta-core" % [LATEST VERSION]
  )

lazy val out = project
  .settings(
    sourceGenerators.in(Compile) += Def.taskDyn {
      val root = baseDirectory.in(ThisBuild).value.toURI.toString
      val from = sourceDirectory.in(in, Compile).value
      val to = sourceManaged.in(Compile).value
      val outFrom = from.toURI.toString.stripSuffix("/").stripPrefix(root)
      val outTo = to.toURI.toString.stripSuffix("/").stripPrefix(root)
      Def.task {
        scalafix
          .in(in, Compile)
          .toTask(s" AuxRule --out-from=$outFrom --out-to=$outTo")
          .value
        (to ** "*.scala").get
      }
    }.taskValue,
    
    // for import statement and if meta annotation is not expanded
    libraryDependencies += "com.github.dmytromitin" %% "auxify-meta-core" % [LATEST VERSION]
  )

Annotated code should be placed in in/src/main/scala. Code generation in out/target/scala-2.13/src_managed/main/scala can be run with sbt out/compile.

Example project is here.

Rewriting with Scalafix

For using rewriting rules with Scalameta + SemanticDB + Scalafix write in project/plugins.sbt

addSbtPlugin("ch.epfl.scala" % "sbt-scalafix" % "0.9.18")

and in build.sbt

// on the top
import com.geirsson.coursiersmall.{Repository => R}
scalafixResolvers in ThisBuild += new R.Maven("https://oss.sonatype.org/content/groups/public/")
scalafixDependencies in ThisBuild += "com.github.dmytromitin" %% "auxify-meta" % [LATEST VERSION]

scalaVersion := "2.13.3"
//scalaVersion := "2.12.11"
//scalaVersion := "2.11.12"

libraryDependencies += "com.github.dmytromitin" %% "auxify-meta-core" % [LATEST VERSION]

addCompilerPlugin(scalafixSemanticdb)

scalacOptions += "-Yrangepos" // for SemanticDB

Rewriting can be run with sbt "scalafix AuxRule" (details are here).

Code generation with Scalameta

For code generating syntacticly with pure Scalameta (without SemanticDB and Scalafix) write in project/build.sbt

resolvers += Resolver.sonatypeRepo("public")
libraryDependencies += "com.github.dmytromitin" %% "auxify-syntactic-meta" % [LATEST VERSION]

and in build.sbt

inThisBuild(Seq(
  scalaVersion := "2.13.3"
  //scalaVersion := "2.12.11"
  //scalaVersion := "2.11.12"
))

lazy val in = project
  .settings(
    libraryDependencies += "com.github.dmytromitin" %% "auxify-meta-core" % [LATEST VERSION]
  )

lazy val out = project
  .settings(
    sourceGenerators in Compile += Def.task {
      import com.github.dmytromitin.auxify.meta.syntactic.ScalametaTransformer
      
      val finder: PathFinder = sourceDirectory.in(in, Compile).value ** "*.scala"
  
      for(inputFile <- finder.get) yield {
        val inputStr = IO.read(inputFile)
        val outputFile = sourceManaged.in(Compile).value / inputFile.name
        val outputStr = ScalametaTransformer.transform(inputStr)
        IO.write(outputFile, outputStr)
        outputFile
      }
    }.taskValue,
    
    // for import statement and if meta annotation is not expanded
    libraryDependencies += "com.github.dmytromitin" %% "auxify-meta-core" % [LATEST VERSION]
  )

Annotated code should be placed in in/src/main/scala. Code generation in out/target/scala-2.13/src_managed/main can be run with sbt out/compile.

Example project is here.