A practical example of a proactive error handler that automatically defines undeclared variables on the fly, allowing the expression to successfully resume execution.

ID: 1190

See: AddHandler, Error = [ErrorInfo], Error handling and control flow, ErrorCode, ErrorHandlerResponse, Handling Errors, Response = [ErrorHandlerResponse] 
				
					using uCalcSoftware;

var uc = new uCalc();

// This handler automatically defines variables when they are first used.
static void AutoDefineHandler(Handle_uCalc h) {
   var uc = new uCalc(h);
   // Check if the error is specifically an undefined identifier
   if (uc.Error.Code == ErrorCode.Undefined_Identifier) {
      Console.WriteLine($"Handler: '{uc.Error.Symbol}' is undefined. Defining it now.");
      uc.DefineVariable(uc.Error.Symbol);

      // Tell the engine to resume the operation
      uc.Error.Response = ErrorHandlerResponse.Resume;
   }
}


uc.Error.AddHandler(AutoDefineHandler);

// 'my_var' doesn't exist yet, but the handler will create it.
var result = uc.EvalStr("my_var = 100; my_var = my_var * 2");

Console.WriteLine($"Final result: {result}");
				
			
Handler: 'my_var' is undefined. Defining it now.
Final result: 200
Explore 600+ other examples
				
					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

// This handler automatically defines variables when they are first used.
void ucalc_call AutoDefineHandler(Handle_uCalc h) {
   auto uc = uCalc(h);
   // Check if the error is specifically an undefined identifier
   if (uc.Error().Code() == ErrorCode::Undefined_Identifier) {
      cout << "Handler: '" << uc.Error().Symbol() << "' is undefined. Defining it now." << endl;
      uc.DefineVariable(uc.Error().Symbol());

      // Tell the engine to resume the operation
      uc.Error().Response(ErrorHandlerResponse::Resume);
   }
}

int main() {
   uCalc uc;
   uc.Error().AddHandler(AutoDefineHandler);

   // 'my_var' doesn't exist yet, but the handler will create it.
   auto result = uc.EvalStr("my_var = 100; my_var = my_var * 2");

   cout << "Final result: " << result << endl;
}
				
			
Handler: 'my_var' is undefined. Defining it now.
Final result: 200
Explore 600+ other examples
				
					Imports System
Imports uCalcSoftware
Public Module Program
   
   '// This handler automatically defines variables when they are first used.
   Public Sub AutoDefineHandler(ByVal h As Handle_uCalc)
      Dim uc As New uCalc(h)
      '// Check if the error is specifically an undefined identifier
      If uc.Error.Code = ErrorCode.Undefined_Identifier Then
         Console.WriteLine($"Handler: '{uc.Error.Symbol}' is undefined. Defining it now.")
         uc.DefineVariable(uc.Error.Symbol)
         
         '// Tell the engine to resume the operation
         uc.Error.Response = ErrorHandlerResponse.Resume
      End If
   End Sub
   
   Public Sub Main()
      Dim uc As New uCalc()
      uc.Error.AddHandler(AddressOf AutoDefineHandler)
      
      '// 'my_var' doesn't exist yet, but the handler will create it.
      Dim result = uc.EvalStr("my_var = 100; my_var = my_var * 2")
      
      Console.WriteLine($"Final result: {result}")
   End Sub
End Module
				
			
Handler: 'my_var' is undefined. Defining it now.
Final result: 200
Explore 600+ other examples