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November 7, 2021 13:39
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| case class EvaluationError( | |
| val evaluating: Evaluate, | |
| val reason: String, | |
| val cause: String | |
| ) | |
| trait Evaluate { | |
| def evaluate: Either[EvaluationError, Double] | |
| } | |
| trait TwoHandEvaluation extends Evaluate { | |
| def evaluateOperands(left: Evaluate, right: Evaluate): Either[EvaluationError, (Double, Double)] = { | |
| for { | |
| l <- left.evaluate.right | |
| r <- right.evaluate.right | |
| } yield { | |
| (l, r) | |
| } | |
| } | |
| } | |
| case class Value(value: Double) extends Evaluate { | |
| def evaluate: Either[EvaluationError,Double] = Right(value) | |
| override def toString(): String = value.toString; | |
| } | |
| case class Add(left: Evaluate, right: Evaluate) extends TwoHandEvaluation { | |
| def evaluate: Either[EvaluationError, Double] = { | |
| for { eval <- evaluateOperands(left, right) } yield { eval._1 + eval._2 } | |
| } | |
| override def toString(): String = "(%s) + (%s)".format(left.toString, right.toString) | |
| } | |
| case class Subtract(left: Evaluate, right: Evaluate) extends TwoHandEvaluation { | |
| def evaluate: Either[EvaluationError, Double] = { | |
| for { eval <- evaluateOperands(left, right) } yield { eval._1 - eval._2 } | |
| } | |
| override def toString(): String = "(%s) - (%s)".format(left.toString, right.toString) | |
| } | |
| case class Multiply(left: Evaluate, right: Evaluate) extends TwoHandEvaluation { | |
| def evaluate: Either[EvaluationError, Double] = { | |
| for { eval <- evaluateOperands(left, right) } yield { eval._1 * eval._2 } | |
| } | |
| override def toString(): String = "(%s) * (%s)".format(left.toString, right.toString) | |
| } | |
| case class Divide(left: Evaluate, right: Evaluate) extends TwoHandEvaluation { | |
| def evaluate: Either[EvaluationError, Double] = { | |
| for { eval <- evaluateOperands(left, right) } yield { | |
| if(eval._2 == 0) { | |
| return Left(EvaluationError( | |
| this, | |
| "Tried to divide by zero", | |
| "Right formula was evaluated as zero, hence this error occured" | |
| )) | |
| } | |
| eval._1 / eval._2 | |
| } | |
| } | |
| override def toString(): String = "(%s) / (%s)".format(left.toString, right.toString) | |
| } | |
| object Main extends App { | |
| val formula = Add(Divide(Subtract(Value(50), Value(10)), Multiply(Value(30), Value(0))), Value(100)); | |
| formula.evaluate match { | |
| case Left(e) => { | |
| println("[!] %s".format(e.reason)) | |
| println(" Evaluating: %s".format(formula.toString)) | |
| println(" Problem: %s".format(e.evaluating.toString)) | |
| println(" Why: %s".format(e.cause)) | |
| } | |
| case Right(value) => println("Evaluated successfully: " + formula.toString + " = " + value) | |
| } | |
| } |
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