Argument as a substring int causes exception

[djolly-fuze]

This sample extensions.conf

[macro-callerid-name-shorten]
exten => s,1,Set(CALLERID(name)=${CALLERID(name):0:${ARG1}})

causes an exception in asterisklint

Traceback (most recent call last):
  File "/usr/local/lib/python3.9/site-packages/asterisklint/config.py", line 186, in __iter__
    self.on_varset(element)
  File "/usr/local/lib/python3.9/site-packages/asterisklint/dialplan.py", line 600, in on_varset
    dialplanvarset = DialplanVarset.from_varset(varset)
  File "/usr/local/lib/python3.9/site-packages/asterisklint/dialplan.py", line 508, in from_varset
    app = App(app, varset.where)
  File "/usr/local/lib/python3.9/site-packages/asterisklint/application.py", line 111, in __init__
    self.parse()
  File "/usr/local/lib/python3.9/site-packages/asterisklint/application.py", line 134, in parse
    self.data = self.parse_inner(self.data)
  File "/usr/local/lib/python3.9/site-packages/asterisklint/application.py", line 149, in parse_inner
    data = VarLoader().parse_variables(data, self.where)
  File "/usr/local/lib/python3.9/site-packages/asterisklint/varfun.py", line 288, in parse_variables
    inner_data = self._process_variable(
  File "/usr/local/lib/python3.9/site-packages/asterisklint/varfun.py", line 330, in _process_variable
    return FuncLoader().process_read_function(data, where)
  File "/usr/local/lib/python3.9/site-packages/asterisklint/varfun.py", line 182, in process_read_function
    return ReadFuncSlice(func, args, start=start, length=length)
  File "/usr/local/lib/python3.9/site-packages/asterisklint/variable.py", line 257, in __init__
    if length < 0:
TypeError: '<' not supported between instances of 'Var' and 'int'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/usr/local/bin/asterisklint", line 34, in <module>
    sys.exit(main(sys.argv[1:], os.environ))
  File "/usr/local/lib/python3.9/site-packages/asterisklint/main.py", line 178, in main
    return command_module.main(args, envs)
  File "/usr/local/lib/python3.9/site-packages/asterisklint/mainutil.py", line 35, in __call__
    return self.handle_args(args)
  File "/usr/local/lib/python3.9/site-packages/asterisklint/commands/dialplan-check.py", line 50, in handle_args
    dialplan = next(iter(parser))
  File "/usr/local/lib/python3.9/site-packages/asterisklint/config.py", line 192, in __iter__
    raise ProgrammingError(str(element.where)) from exc
asterisklint.config.ProgrammingError: An unexpected exception was raised. This is most likely a bug in the asterisklint library. If you can reproduce the problem and file an issue on the bug tracker, that would be nice. Further info: extensions.conf:2

Replacing ${ARG1} with a hardcoded integer works as expected, but for my logic, it must be a variable.

I can't find a decent workaround as wrapping ARG1 with TRUNC and MATH function also produce similar comparison exceptions but different instances instead of 'Var', 'ReadFunc' and 'Expr' respectively.