Scala Case Ordering Benchmark

package org.example

import annotation.tailrec
import com.google.caliper.Param

class CaseOrder extends SimpleScalaBenchmark {

  abstract class Expr
  case class Var(name: String) extends Expr
  case class Number(num: Double) extends Expr
  case class UnOp(operator: String, arg: Expr) extends Expr
  case class BinOp(operator: String, left: Expr, right: Expr) extends Expr

  object ExprFirst {
    def simplify(expr: Expr): Expr = expr match {
      // Some basic simplification rules...
      case UnOp("-", UnOp("-", e)) => simplify(e) // Double negation
      case BinOp("+", e, Number(0)) => simplify(e) // Adding zero
      case BinOp("-", e, Number(0)) => simplify(e) // Subtracting zero
      case BinOp("*", e, Number(1)) => simplify(e) // Multiplying by one
      case BinOp("*", e, Number(0)) => Number(0) // Multiplying by zero
      case _ => expr // Default, could not simplify given above rules
    }
  }

  object ExprLast {
    def simplify(expr: Expr): Expr = expr match {
      // Some basic simplification rules...
      case BinOp("+", e, Number(0)) => simplify(e) // Adding zero
      case BinOp("-", e, Number(0)) => simplify(e) // Subtracting zero
      case BinOp("*", e, Number(1)) => simplify(e) // Multiplying by one
      case BinOp("*", e, Number(0)) => Number(0) // Multiplying by zero
      case UnOp("-", UnOp("-", e)) => simplify(e) // Double negation
      case _ => expr // Default, could not simplify given above rules
    }
  }

  @tailrec
  private def buildInput( start: Expr, n: Int ): Expr =
    if( n == 0 ) start
    else buildInput( UnOp("-", start ), n-1)

  val input = buildInput( Var("x"), 100000 )

  def timeForFirst( reps: Int ) = repeat(reps) {
    ExprFirst.simplify( input )
  }

  def timeForLast( reps: Int ) = repeat(reps) {
    ExprLast.simplify( input )
  }

}