processor.py

import json

class InputValidationError(Exception):
    pass

def validate_input(user_input):
    if not isinstance(user_input, str) or not user_input:
        raise InputValidationError('Input must be a non-empty string.')

def process_user_input(user_input):
    validate_input(user_input)
    # Process the valid input
    return {'result': user_input.upper()}

def main():
    while True:
        user_input = input('Enter some text (or type exit to quit): ')
        if user_input.lower() == 'exit':
            break
        try:
            result = process_user_input(user_input)
            print(json.dumps(result))
        except InputValidationError as e:
            print(f'Error: {e}')

if __name__ == '__main__':
    main()