     func runSchemeCode() {
         
         startSpinner()
+        
+        // If we move to only support macOS 10.12, can use the improved time difference code adapted from JeremyP's answer to http://stackoverflow.com/questions/24755558/measure-elapsed-time-in-swift.  Instead we'll use JeremyP's NSDate version instead.
+        let startTime = NSDate();
+        
     
         // Path to Chez Scheme
         // Perhaps this should be settable in a preferences panel.

            print("error datastring for process \( self.task.processIdentifier ): \(errorDatastring)")
        }
    }
}
            }
            
            func onTestSuccess(inputField: NSTextField, outputField: NSTextField, label: NSTextField) {
                let endTime = NSDate();
                let timeInterval: Double = endTime.timeIntervalSinceDate(startTime);
                
                inputField.textColor = .blackColor()
                outputField.textColor = .blackColor()
                // formatting from realityone's answer to http://stackoverflow.com/questions/24051314/precision-string-format-specifier-in-swift
                label.stringValue = String(format: "Success (%.2f s)",  timeInterval)
            }
            
            func onTestSyntaxError(inputField: NSTextField, outputField: NSTextField, spinner: NSProgressIndicator, label: NSTextField) {
