title: How to catch exception when use NSExpression (swift 3)
body: <pre><code>    import UIKit
  
  
  func calculatorFromString(colculation:String)-&gt;Double{
      let mathExpression = try NSExpression(format: colculation)
      let mathValue = mathExpression.expressionValue(with: nil, context: nil) as? Double
          return mathValue!
  }
  
  calculatorFromString(colculation: "5*(1+4)")
  </code></pre>
  
  <p>when I set colculation equal "5*(1+4)))", this is a error and I dont know how to catch exception. Thank you!</p>