Merge pull request #28 from MakeNowJust-Labo/lazy

CHANGELOG.md

@@ -5,6 +5,7 @@ Changes:
 - `lite-diff`: Initial release ([#16](https://github.com/MakeNowJust-Labo/lite/pull/16))
 - `lite-pfix`: Initial release ([#27](https://github.com/MakeNowJust-Labo/lite/pull/27))
 - `lite-shohw`: Use `lite-pfix` ([#27](https://github.com/MakeNowJust-Labo/lite/pull/27))
+- `lite-crazy`: Initial release ([#28](https://github.com/MakeNowJust-Labo/lite/pull/28))
 - Support Scala 2.13.6
 - Support Scala 3.0.1 ([#23](https://github.com/MakeNowJust-Labo/lite/pull/23))
 - Update sbt to 1.5.5 ([#24](https://github.com/MakeNowJust-Labo/lite/pull/24))

README.md

@@ -7,6 +7,7 @@
 
 ## Libraries
 
+- [**lite-crazy**](modules/lite-crazy): A lazy-evaluated value cell and time travelling state monads implementations.
 - [**lite-diff**](modules/lite-diff): Computes a diff between two sequences.
 - [**lite-gimei**](modules/lite-gimei): A generator of Japanese dummy names and addresses with furigana.
 - [**lite-grapheme**](modules/lite-grapheme): Iterates the given string on each grapheme cluster.

build.sbt

@@ -29,7 +29,7 @@ ThisBuild / semanticdbVersion := scalafixSemanticdb.revision
 ThisBuild / scalafixDependencies += "com.github.liancheng" %% "organize-imports" % "0.5.0"
 ThisBuild / scalafixDependencies += "com.github.vovapolu" %% "scaluzzi" % "0.1.18"
 
-val crossProjectNames = Seq("diff", "gimei", "grapheme", "romaji", "show")
+val crossProjectNames = Seq("crazy", "diff", "gimei", "grapheme", "pfix", "romaji", "show")
 val platformSuffices = Seq("JVM", "JS", "Native")
 platformSuffices.flatMap { platform =>
   addCommandAlias(s"test$platform", crossProjectNames.map(name => s"$name$platform/test").mkString("; "))
@@ -42,12 +42,42 @@ lazy val root = project
     publish / skip := true,
     coverageEnabled := false
   )
+  .aggregate(crazyJVM, crazyJS, crazyNative)
   .aggregate(diffJVM, diffJS, diffNative)
   .aggregate(gimeiJVM, gimeiJS, gimeiNative)
   .aggregate(graphemeJVM, graphemeJS, graphemeNative)
   .aggregate(romajiJVM, romajiJS, romajiNative)
+  .aggregate(pfixJVM, pfixJS, pfixNative)
   .aggregate(showJVM, showJS, showNative)
 
+lazy val crazy = crossProject(JVMPlatform, JSPlatform, NativePlatform)
+  .in(file("modules/lite-crazy"))
+  .settings(
+    name := "lite-crazy",
+    console / initialCommands :=
+      """|import codes.quine.labo.lite.crazy._
+         |""".stripMargin,
+    Compile / console / scalacOptions -= "-Wunused",
+    Test / console / scalacOptions -= "-Wunused",
+    // Set URL mapping of scala standard API for Scaladoc.
+    apiMappings ++= scalaInstance.value.libraryJars
+      .filter(file => file.getName.startsWith("scala-library") && file.getName.endsWith(".jar"))
+      .map(_ -> url(s"http://www.scala-lang.org/api/${scalaVersion.value}/"))
+      .toMap,
+    // Settings for test:
+    libraryDependencies += "org.scalameta" %%% "munit" % "0.7.27" % Test,
+    testFrameworks += new TestFramework("munit.Framework")
+  )
+  .jsSettings(Test / scalaJSLinkerConfig ~= { _.withModuleKind(ModuleKind.CommonJSModule) })
+  .nativeSettings(
+    crossScalaVersions := Seq("2.13.6"),
+    coverageEnabled := false
+  )
+
+lazy val crazyJVM = crazy.jvm
+lazy val crazyJS = crazy.js
+lazy val crazyNative = crazy.native
+
 lazy val diff = crossProject(JVMPlatform, JSPlatform, NativePlatform)
   .in(file("modules/lite-diff"))
   .settings(

modules/lite-crazy/README.md

@@ -0,0 +1,18 @@
+# lite-crazy
+
+> A lazy-evaluated value cell and time travelling state monads implementations.
+
+[![Maven Central](https://img.shields.io/maven-central/v/codes.quine.labo/lite-crazy_2.13?logo=scala&style=for-the-badge)](https://search.maven.org/artifact/codes.quine.labo/lite-crazy_2.13)
+
+## Install
+
+Insert the following to your `build.sbt`.
+
+```sbt
+libraryDependencies += "codes.quine.labo" %% "lite-crazy" % "0.3.0"
+```
+
+## Reference
+
+- <https://lukepalmer.wordpress.com/2008/08/10/mindfuck-the-reverse-state-monad/>
+- <https://blog.csongor.co.uk/time-travel-in-haskell-for-dummies/>

modules/lite-crazy/shared/src/main/scala/codes/quine/labo/lite/crazy/Lazy.scala

@@ -0,0 +1,38 @@
+package codes.quine.labo.lite.crazy
+
+/** Lazy is a lazy-evaluated value cell. */
+final class Lazy[A] private (private[this] var thunk: () => A) {
+
+  private[this] var cache: Option[A] = None
+
+  /** Returns an underlying value. */
+  def value: A = cache match {
+    case Some(x) => x
+    case None =>
+      synchronized {
+        val x = thunk()
+        thunk = null
+        cache = Some(x)
+        x
+      }
+  }
+
+  /** Applies an underlying value to the given mapping, and returns a new lazy cell holds this result. */
+  def map[B](f: A => B): Lazy[B] = Lazy(f(value))
+
+  /** Applies an underlying value to the given mapping, and returns a new lazy cell holds flattened result. */
+  def flatMap[B](f: A => Lazy[B]): Lazy[B] = Lazy(f(value).value)
+}
+
+object Lazy {
+
+  /** Returns a lazy-evaluated value cell with the given value. */
+  def apply[A](x: => A): Lazy[A] = new Lazy(() => x)
+
+  /** Returns an lazy-evaluated value cell getting from fixpoint function. */
+  def fix[A](f: Lazy[A] => A): Lazy[A] = {
+    var lx: Lazy[A] = null
+    lx = Lazy(f(lx))
+    lx
+  }
+}

modules/lite-crazy/shared/src/main/scala/codes/quine/labo/lite/crazy/RState.scala

@@ -0,0 +1,42 @@
+package codes.quine.labo.lite.crazy
+
+/** RState is reversed state monad implementation. */
+final case class RState[S, A](run: Lazy[S] => (Lazy[S], Lazy[A])) {
+
+  /** Applies a result value to the given mapping, and returns a new reversed state monad holds this result. */
+  def map[B](f: Lazy[A] => Lazy[B]): RState[S, B] = flatMap(lx => RState.pure(f(lx)))
+
+  /** Applies a result value to the given mapping, and returns a new reversed state monad holds flattened result.
+    * Hence the mapping requires a lazy cell as its argument, we can write an action depends on future state.
+    */
+  def flatMap[B](f: Lazy[A] => RState[S, B]): RState[S, B] =
+    RState[S, B] { ls0 =>
+      type Fix = (Lazy[(Lazy[S], Lazy[A])], Lazy[(Lazy[S], Lazy[B])], Lazy[S], Lazy[S], Lazy[A], Lazy[B])
+      val lfix = Lazy.fix[Fix] { lfix =>
+        val ls2x = Lazy(run(lfix.value._3))
+        val ls1y = Lazy(f(lfix.value._5).run(ls0))
+        val ls1 = Lazy(ls1y.value._1.value)
+        val ls2 = Lazy(ls2x.value._1.value)
+        val lx = Lazy(ls2x.value._2.value)
+        val ly = Lazy(ls1y.value._2.value)
+        (ls2x, ls1y, ls1, ls2, lx, ly)
+      }
+      val (_, _, _, ls2, _, ly) = lfix.value
+      (ls2, ly)
+    }
+}
+
+object RState {
+
+  /** Returns a reversed state monad holds the specified value as its result value. */
+  def pure[S, A](lx: Lazy[A]): RState[S, A] = RState(ls => (ls, lx))
+
+  /** Returns a reversed state monad holds a future state as its result value. */
+  def get[S]: RState[S, S] = RState(ls => (ls, ls))
+
+  /** Returns a reversed state monad for putting the specified value to its state. */
+  def put[S](ls: Lazy[S]): RState[S, Unit] = RState(_ => (ls, Lazy(())))
+
+  /** Returns a reversed state monad for modifying its state by the given mapping. */
+  def modify[S](f: Lazy[S] => Lazy[S]): RState[S, Unit] = RState(ls => (f(ls), Lazy(())))
+}

modules/lite-crazy/shared/src/main/scala/codes/quine/labo/lite/crazy/Tardis.scala

@@ -0,0 +1,64 @@
+package codes.quine.labo.lite.crazy
+
+/** Tardis a state monad implementation holds both of backward and forward states. */
+final case class Tardis[BW, FW, A](run: (Lazy[BW], Lazy[FW]) => (Lazy[BW], Lazy[FW], Lazy[A])) {
+
+  /** Applies a result value to the given mapping, and returns a new tardis monad holds this result. */
+  def map[B](f: Lazy[A] => Lazy[B]): Tardis[BW, FW, B] = flatMap(lx => Tardis.pure(f(lx)))
+
+  /** Applies a result value to the given mapping, and returns a new tardis monad holds flattened result.
+    * Hence the mapping requires lazy cells as its arguments, we can write an action depends on both of future and past state.
+    */
+  def flatMap[B](f: Lazy[A] => Tardis[BW, FW, B]): Tardis[BW, FW, B] =
+    Tardis { case (lb0, lf0) =>
+      type Fix = (
+          Lazy[(Lazy[BW], Lazy[FW], Lazy[A])],
+          Lazy[(Lazy[BW], Lazy[FW], Lazy[B])],
+          Lazy[BW],
+          Lazy[BW],
+          Lazy[FW],
+          Lazy[FW],
+          Lazy[A],
+          Lazy[B]
+      )
+      val lfix = Lazy.fix[Fix] { lfix =>
+        val lb2f1x = Lazy(run(lfix.value._3, lf0))
+        val lb1f2y = Lazy(f(lfix.value._7).run(lb0, lfix.value._5))
+        val lb1 = Lazy(lb1f2y.value._1.value)
+        val lb2 = Lazy(lb2f1x.value._1.value)
+        val lf1 = Lazy(lb2f1x.value._2.value)
+        val lf2 = Lazy(lb1f2y.value._2.value)
+        val lx = Lazy(lb2f1x.value._3.value)
+        val ly = Lazy(lb1f2y.value._3.value)
+        (lb2f1x, lb1f2y, lb1, lb2, lf1, lf2, lx, ly)
+      }
+      val (_, _, _, lb2, _, lf2, _, ly) = lfix.value
+      (lb2, lf2, ly)
+    }
+}
+
+object Tardis {
+
+  /** Returns a new tardis monad holds the specified value as its result. */
+  def pure[BW, FW, A](lx: Lazy[A]): Tardis[BW, FW, A] = Tardis((lb, lf) => (lb, lf, lx))
+
+  /** Returns a new tardis monad holds a backward state as its result. */
+  def getBackward[BW, FW]: Tardis[BW, FW, BW] = Tardis((lb, lf) => (lb, lf, lb))
+
+  /** Returns a new tardis monad for putting the specified value to a backward state. */
+  def putBackward[BW, FW](lb: Lazy[BW]): Tardis[BW, FW, Unit] = Tardis((_, lf) => (lb, lf, Lazy(())))
+
+  /** Returns a new tardis monad for modifying a backward state by the given mapping. */
+  def modifyBackward[BW, FW](f: Lazy[BW] => Lazy[BW]): Tardis[BW, FW, Unit] =
+    Tardis((lb, lf) => (f(lb), lf, Lazy(())))
+
+  /** Returns a new tardis monad holds a forward state as its result. */
+  def getForward[BW, FW]: Tardis[BW, FW, FW] = Tardis((lb, lf) => (lb, lf, lf))
+
+  /** Returns a new tardis monad for putting the specified value to a forward state. */
+  def putForward[BW, FW](lf: Lazy[FW]): Tardis[BW, FW, Unit] = Tardis((lb, _) => (lb, lf, Lazy(())))
+
+  /** Returns a new tardis monad for modifying a forward state by the given mapping. */
+  def modifyForward[BW, FW](f: Lazy[FW] => Lazy[FW]): Tardis[BW, FW, Unit] =
+    Tardis((lb, lf) => (lb, f(lf), Lazy(())))
+}

modules/lite-crazy/shared/src/main/scala/codes/quine/labo/lite/crazy/implicits.scala

@@ -0,0 +1,12 @@
+package codes.quine.labo.lite.crazy
+
+/** implicits provides convenience implicit conversions. */
+object implicits {
+  import scala.language.implicitConversions
+
+  /** Wraps any value to lazy cell. */
+  implicit def any2lazy[A](x: => A): Lazy[A] = Lazy(x)
+
+  /** Unwraps any value from a lazy cell. */
+  implicit def lazy2any[A](lx: Lazy[A]): A = lx.value
+}

modules/lite-crazy/shared/src/test/scala/codes/quine/labo/lite/crazy/LazySuite.scala

@@ -0,0 +1,28 @@
+package codes.quine.labo.lite.crazy
+
+class LazySuite extends munit.FunSuite {
+  test("Lazy.apply") {
+    var x = 0
+    val lx = Lazy {
+      x += 1
+      x
+    }
+    assertEquals(x, 0)
+    assertEquals(lx.value, 1)
+    assertEquals(x, 1)
+    assertEquals(lx.value, 1)
+  }
+
+  test("Lazy.fix") {
+    val lxs = Lazy.fix[LazyList[Int]](lxs => LazyList.cons(1, lxs.value).scanLeft(0)(_ + _))
+    assertEquals(lxs.value.take(10), LazyList(0, 1, 1, 2, 3, 5, 8, 13, 21, 34))
+  }
+
+  test("Lazy#map") {
+    assertEquals(Lazy(1).map(_ + 2).value, 3)
+  }
+
+  test("Lazy#flatMap") {
+    assertEquals(Lazy(1).flatMap(x => Lazy(x + 2)).value, 3)
+  }
+}

modules/lite-crazy/shared/src/test/scala/codes/quine/labo/lite/crazy/RStateSuite.scala

@@ -0,0 +1,21 @@
+package codes.quine.labo.lite.crazy
+
+class RStateSuite extends munit.FunSuite {
+  // https://lukepalmer.wordpress.com/2008/08/10/mindfuck-the-reverse-state-monad/
+  test("RState: fibs") {
+    import codes.quine.labo.lite.crazy.implicits._
+
+    def cumulativeSums(xs: LazyList[Int]): LazyList[Int] = xs.scanLeft(0)(_ + _)
+
+    def computeFibs(): RState[LazyList[Int], LazyList[Int]] = for {
+      fibs <- RState.get[LazyList[Int]]
+      _ <- RState.modify[LazyList[Int]](cumulativeSums(_))
+      _ <- RState.put[LazyList[Int]](LazyList.cons(1, fibs))
+    } yield fibs
+
+    assertEquals(
+      computeFibs().run(LazyList.empty[Int])._2.take(15),
+      LazyList(0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377)
+    )
+  }
+}