Example 3

The correct .NET behaviour when an APL function fails with an error is to throw an exception, and this example shows how to do it.

In the .NET Framework, exceptions are implemented as .NET Classes. The base exception is implemented by the System.Exception class, but there are a number of super classes, such as System.ArgumentException and System.ArithmeticException that inherit from it.

⎕SIGNAL may be used to throw an exception. To do so, its right argument should be 90 and its left argument should be an object of type System.Exception or an object that inherits from System.Exception.

When you create the instance of the Exception class, you may specify a string (which will turn up in its Message property) containing information about the error.

aplclasses3.dws contains an improved version of the CTOR constructor function.

     ∇ CTOR IO;EX
[1]   :Access public
[2]   :Signature CTOR Int32 IO
[3]   :Implements constructor
[4]   :If IO∊0 1
[5]      ⎕IO←IO
[6]   :Else
[7]      EX←⎕NEW ArgumentException,⊂⊂'IndexOrigin must be 
                                      0 or 1'
[8]      EX ⎕SIGNAL 90
[9]   :EndIf
     ∇

Load aplclasses3.dws and export aplclasses3.dll as before.

Figure 1: aplclasses3_1

Figure 2: aplclasses3_2

program.cs

The following C# source, called aplclasses2\Framework\program.cs, contains code to catch the exception and to display the exception message.

using System;
using APLClasses;
public class MainClass
    {
    public static void Main()
        {
try
    {
        Primitives apl = new Primitives(2);
        int[] rslt = apl.IndexGen(10);

        for (int i=0;i<rslt.Length;i++)
            Console.WriteLine(rslt[i]);
}
catch (Exception e)
    {
    Console.WriteLine(e.Message);
    }
        }

    }   

Using VS, open the solution file d:\aplclasses\aplclasses3\Framework\project.sln and view program.cs.

Figure 3: aplclasses3_3

Click Debug/Start Without debugging (or press Ctrl+F5) to run the program. The results are shown in a console window.

Figure 4: aplclasses3_4