Initial version -- ~45 minutes of poking around.

.gitignore

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+target/
+project/target/
+project/project/
+.version

.pre-commit-config.yaml

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+---
+repos:
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v4.5.0
+    hooks:
+      - id: end-of-file-fixer
+      - id: trailing-whitespace
+      - id: fix-byte-order-marker
+      - id: mixed-line-ending
+        args: ['--fix=lf']
+        description: Enforces using only 'LF' line endings.
+      - id: trailing-whitespace
+  - repo: https://git.garrity.co/garrity-software/gs-pre-commit-scala
+    rev: v1.0.1
+    hooks:
+      - id: scalafmt

.scalafmt.conf

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+// See: https://github.com/scalameta/scalafmt/tags for the latest tags.
+version = 3.8.1
+runner.dialect = scala3
+maxColumn = 80
+
+rewrite {
+    rules = [RedundantBraces, RedundantParens, Imports, SortModifiers]
+    imports.expand = true
+    imports.sort = scalastyle
+    redundantBraces.ifElseExpressions = true
+    redundantBraces.stringInterpolation = true
+}
+
+indent {
+    main = 2
+    callSite = 2
+    defnSite = 2
+    extendSite = 4
+    withSiteRelativeToExtends = 2
+    commaSiteRelativeToExtends = 2
+}
+
+align {
+    preset = more
+    openParenCallSite = false
+    openParenDefnSite = false
+}
+
+newlines {
+    implicitParamListModifierForce = [before,after]
+    topLevelStatementBlankLines = [
+        {
+            blanks = 1
+        }
+    ]
+    afterCurlyLambdaParams = squash
+}
+
+danglingParentheses {
+    defnSite = true
+    callSite = true
+    ctrlSite = true
+    exclude = []
+}
+
+verticalMultiline {
+    atDefnSite = true
+    arityThreshold = 2
+    newlineAfterOpenParen = true
+}
+
+comments {
+    wrap = standalone
+}
+
+docstrings {
+    style = "SpaceAsterisk"
+    oneline = unfold
+    wrap = yes
+    forceBlankLineBefore = true
+}
+
+project {
+  excludePaths = [
+    "glob:**target/**",
+    "glob:**.metals/**",
+    "glob:**.bloop/**",
+    "glob:**.bsp/**",
+    "glob:**metals.sbt",
+    "glob:**.git/**"
+  ]
+}

README.md

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+# fizzbuzz
+
+This project is an over-engineered fizzbuzz to buzz your fizz.

build.sbt

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+val scala3: String = "3.8.4"
+
+ThisBuild / scalaVersion  := scala3
+ThisBuild / gsProjectName := "fizzbuzz"
+
+ThisBuild / externalResolvers := Seq(
+  "Garrity Software Mirror" at "https://maven.garrity.co/releases",
+  "Garrity Software Releases" at "https://maven.garrity.co/gs"
+)
+
+lazy val sharedSettings = Seq(
+  scalaVersion        := scala3,
+  version             := calVer.value,
+  publish / skip      := true,
+  publishLocal / skip := true,
+  publishArtifact     := false
+)
+
+val Deps = new {
+  val Cats = new {
+    val Core: ModuleID   = "org.typelevel" %% "cats-core"   % "2.13.0"
+    val Effect: ModuleID = "org.typelevel" %% "cats-effect" % "3.7.0"
+  }
+
+  val Fs2 = new {
+    private val Version: String = "3.13.0"
+
+    val Core: ModuleID = "co.fs2" %% "fs2-core" % Version
+    val IO: ModuleID   = "co.fs2" %% "fs2-io"   % Version
+  }
+
+  val Gs = new {
+    val Std: ModuleID     = "gs" %% "gs-std-core-v0"     % "0.1.3"
+    val Datagen: ModuleID = "gs" %% "gs-datagen-core-v0" % "0.4.1"
+  }
+
+  val MUnit: ModuleID = "org.scalameta" %% "munit" % "1.3.0"
+}
+
+lazy val testSettings = Seq(
+  libraryDependencies ++= Seq(
+    Deps.MUnit      % Test,
+    Deps.Gs.Datagen % Test
+  )
+)
+
+lazy val fizzbuzz = project
+  .in(file("."))
+  .settings(sharedSettings)
+  .settings(testSettings)
+  .settings(name := s"${gsProjectName.value}")
+  .settings(fork := true)
+  .settings(
+    libraryDependencies ++= Seq(
+      Deps.Cats.Core,
+      Deps.Cats.Effect,
+      Deps.Fs2.Core
+    )
+  )

project/build.properties

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+sbt.version=1.12.11

project/plugins.sbt

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+def selectCredentials(): Credentials =
+  if ((Path.userHome / ".sbt" / ".credentials").exists())
+    Credentials(Path.userHome / ".sbt" / ".credentials")
+  else
+    Credentials.apply(
+      realm = "Reposilite",
+      host = "maven.garrity.co",
+      userName = sys.env
+        .get("GS_MAVEN_USER")
+        .getOrElse(
+          throw new RuntimeException(
+            "You must either provide ~/.sbt/.credentials or specify the GS_MAVEN_USER environment variable."
+          )
+        ),
+      passwd = sys.env
+        .get("GS_MAVEN_TOKEN")
+        .getOrElse(
+          throw new RuntimeException(
+            "You must either provide ~/.sbt/.credentials or specify the GS_MAVEN_TOKEN environment variable."
+          )
+        )
+    )
+
+credentials += selectCredentials()
+
+externalResolvers := Seq(
+  "Garrity Software Mirror" at "https://maven.garrity.co/releases",
+  "Garrity Software Releases" at "https://maven.garrity.co/gs"
+)
+
+addSbtPlugin("org.scoverage" % "sbt-scoverage"        % "2.4.4")
+addSbtPlugin("gs"            % "sbt-garrity-software" % "0.7.0")
+addSbtPlugin("gs"            % "sbt-gs-calver"        % "0.2.0")

src/main/scala/gs/fizzbuzz/Condition.scala

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+package gs.fizzbuzz
+
+import cats.Applicative
+
+trait Condition[F[_], Input, Output]:
+  def matches(input: Input): F[Boolean]
+  def output: Output
+end Condition
+
+object Condition:
+
+  final class Noop[F[_]: Applicative, Input] extends Condition[F, Input, Nothing]:
+    override def matches(input: Input): F[Boolean] = 
+      Applicative[F].pure(false)
+    override def output: Nothing = 
+      throw new IllegalStateException("No-op condition cannot produce output.")
+
+end Condition

src/main/scala/gs/fizzbuzz/DefaultCondition.scala

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+package gs.fizzbuzz
+
+import cats.Applicative
+import cats.Monoid
+
+final class DefaultCondition[F[_]: Applicative, Input, Out](
+  val comparison: Input,
+  val output: Out,
+  val operator: Monoid[Input]
+)(using CanEqual[Input, Input]) extends Condition[F, Input, Out]:
+
+  override def matches(input: Input): F[Boolean] = 
+    Applicative[F].pure(
+      operator.combine(input, comparison) == operator.empty
+    )

src/main/scala/gs/fizzbuzz/DefaultFizzBuzz.scala

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+package gs.fizzbuzz
+
+import cats.syntax.all.*
+import fs2.Pipe
+import cats.FlatMap
+
+class DefaultFizzBuzz[F[_]: FlatMap, Input, Out](
+  val fizzCondition: Condition[F, Input, Out],
+  val buzzCondition: Condition[F, Input, Out]
+) extends FizzBuzz[F, Input, Out]:
+  def evaluate(input: Input): F[Result[Out]] = 
+    for
+      fizz <- fizzCondition.matches(input)
+      buzz <- buzzCondition.matches(input)
+    yield 
+      if fizz && buzz then
+        Result.FizzBuzz(fizzCondition.output, buzzCondition.output)
+      else if fizz then
+        Result.Fizz(fizzCondition.output)
+      else if buzz then
+        Result.Buzz(buzzCondition.output)
+      else
+        Result.Unmatched
+
+  def pipe(): Pipe[F, Input, Result[Out]] = in => in.evalMap(evaluate)
+end DefaultFizzBuzz

src/main/scala/gs/fizzbuzz/FizzBuzz.scala

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+package gs.fizzbuzz
+
+import fs2.Pipe
+
+trait FizzBuzz[F[_], Input, Out]:
+  def evaluate(input: Input): F[Result[Out]] 
+  def pipe(): Pipe[F, Input, Result[Out]]
+end FizzBuzz

src/main/scala/gs/fizzbuzz/Main.scala

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+package gs.fizzbuzz
+
+import cats.Monoid
+import cats.effect.IO
+import cats.effect.IOApp
+import cats.effect.ExitCode
+
+object Main extends IOApp:
+  override def run(args: List[String]): IO[ExitCode] = 
+    val op: Monoid[Long] = new Monoid[Long] {
+      override def empty: Long = 0L
+      override def combine(x: Long, y: Long): Long = x % y
+    }
+
+    val fizzCond: Condition[IO, Long, String] = new DefaultCondition(
+      comparison = 3L,
+      output = "Fizz",
+      operator = op
+    )
+
+    val buzzCond: Condition[IO, Long, String] = new DefaultCondition(
+      comparison = 5L,
+      output = "Buzz",
+      operator = op
+    )
+
+    val fb: FizzBuzz[IO, Long, String] = new DefaultFizzBuzz[IO, Long, String](
+      fizzCondition = fizzCond,
+      buzzCondition = buzzCond
+    )
+
+    for 
+      ex1 <- fb.evaluate(15)
+      ex2 <- fb.evaluate(9)
+      ex3 <- fb.evaluate(20)
+      ex4 <- fb.evaluate(13)
+      _ <- IO.println(ex1)
+      _ <- IO.println(ex2)
+      _ <- IO.println(ex3)
+      _ <- IO.println(ex4)
+    yield
+      ExitCode.Success

src/main/scala/gs/fizzbuzz/Result.scala

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+package gs.fizzbuzz
+
+sealed trait Result[+Out]
+
+object Result:
+
+  case class Fizz[Out](fizz: Out) extends Result[Out]
+  case class Buzz[Out](buzz: Out) extends Result[Out]
+  case class FizzBuzz[Out](fizz: Out, buzz: Out) extends Result[Out]
+  case object Unmatched extends Result[Nothing]:
+    override def toString(): String = "unmatched"
+
+end Result