Error Handling

Error handling is an important part of writing maintainable code. Radon has a powerful exception handler. It can handle exceptions that may occur during the execution of a block of code.

Handling exceptions

In Radon, try-catch blocks are used for error handling. The try block contains the code that may throw an exception. The catch block contains the code that handles the exception.

try {
    # code that may throw an exception (in this case, zero division)
    a = 1 / 0
} catch as err {
    # code that handles the exception
    print("Exception caught: " + err)
}

Output:

Exception caught: Division by zero

Don't forget to use the as keyword to assign the exception to a variable. The variable can be used to get the exception message. If you don't want to use the exception message, you can omit the variable.

try {
    # code that may throw an exception
    a = 1 / 0
} catch as _ {
    # code that handles the exception
    print("Exception caught")
}

Output:

Exception caught

Raise exceptions

In Radon, errors can be raised explicitly using the raise keyword. This is useful for enforcing certain conditions or for creating custom error messages.

Radon has a standard radiation module for Error Types (you can type radiation.errors in the shell to view a list of available error types)

import radiation

if 2 != 4 {
    raise radiation.ValueError("2 != 4")
}

Output:

Radiation (most recent call last):
  File <stdin>, line 2
ValueError: 2 + 2 != 4

    raise radiation.ValueError("2 + 2 != 4")
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Defining custom error types

To define custom errors, you need to define a function that returns a string as the error message.

Example

fun CustomError(file) {
    return "Something went wrong in " + file
}

raise CustomError("custom-error.rn")

Output:

Radiation (most recent call last):
  File <stdin>, line 5
FunctionError: Something went wrong in custom-error.rn

raise CustomError("custom-error.rn")
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

When the exception is raised, the program stops executing and the exception is propagated up the call stack. The exception can be caught by a try block. If the exception is not caught, the program stops executing and the exception is printed to the console.