StandardForm errors given an expression when the first argument is a String

[rocky]

Description

When we have an Expression where the first element is a String, and other arguments, StandardForm formatting throw an unrecoverable error.

How to Reproduce and Output Given

In[1]:= xx = "a string"; StringTake[xx[0]]
StringTake::argr: StringTake called with 1 argument; 2 arguments are expected.
Traceback (most recent call last):
  File "/home/rocky/.pyenv/versions/3.13.12/bin/mathics3", line 7, in <module>
    sys.exit(main())
             ~~~~^^
  File "tmp/Mathics3/mathics-core/mathics/__main__.py", line 632, in main
    interactive_eval_loop(shell, args.full_form, args.strict_wl_output)
    ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "tmp/Mathics3/mathics-core/mathics/__main__.py", line 372, in interactive_eval_loop
    result = evaluation.evaluate(query, timeout=settings.TIMEOUT)
  File "tmp/Mathics3/mathics-core/mathics/core/evaluation.py", line 277, in evaluate
    result = evaluate()
  File "tmp/Mathics3/mathics-core/mathics/core/evaluation.py", line 270, in evaluate
    return self.format_output(self.last_eval, format)
           ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
  File "tmp/Mathics3/mathics-core/mathics/core/evaluation.py", line 406, in format_output
    result = format_element(expr, self, SymbolOutputForm)
  File "tmp/Mathics3/mathics-core/mathics/format/box/makeboxes.py", line 299, in format_element
    result_box = apply_makeboxes_rules(formatted_expr, evaluation, form)
  File "tmp/Mathics3/mathics-core/mathics/format/box/makeboxes.py", line 127, in apply_makeboxes_rules
    return eval_generic_makeboxes(expr, form, evaluation)
  File "tmp/Mathics3/mathics-core/mathics/format/box/makeboxes.py", line 227, in eval_generic_makeboxes
    return printform_callback(elements[0], evaluation)
  File "tmp/Mathics3/mathics-core/mathics/builtin/forms/print.py", line 260, in eval_makeboxes_outputform
    text_outputform = str(render_output_form(expr, evaluation, **kwargs))
                          ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "tmp/Mathics3/mathics-core/mathics/format/form/outputform.py", line 267, in render_output_form
    result = callback(format_expr, evaluation, **kwargs)
  File "tmp/Mathics3/mathics-core/mathics/format/form/outputform.py", line 107, in _default_render_output_form
    elements = [render_output_form(elem, evaluation) for elem in expr.elements]
                ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^
  File "tmp/Mathics3/mathics-core/mathics/format/form/outputform.py", line 267, in render_output_form
    result = callback(format_expr, evaluation, **kwargs)
  File "tmp/Mathics3/mathics-core/mathics/format/form/outputform.py", line 862, in string_render_output_form
    return render_string(expr, **kwargs)
  File "tmp/Mathics3/mathics-core/mathics/format/render/text.py", line 167, in string
    if value.startswith('"') and value.endswith('"'):  # nopep8
       ^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'startswith'
08

Expected behavior

No error

Workarounds

#1848 is a workaround.

Priority

Nothing special; just something noticed.

Additional context

The problem stems from the fact that we have:

<Expression: <String: "a string">[<Integer: 0>]>>

And formatting finds the head to be a String and formats as though the Expression is a string.
Expressions do not have a ".value" attribute, or it is None.

This is the code in render_output_form of mathics.format.form.outputform that is wrong:

def render_output_form(expr: BaseElement, evaluation: Evaluation, **kwargs):
    """
    Build a pretty-print text from an `Expression`
    """
...    
    head = format_expr.get_head()
    lookup_name: str = head.get_name() or head.get_lookup_name()
    callback = EXPR_TO_OUTPUTFORM_TEXT_MAP.get(lookup_name, None)

but I don't know what the right thing to do here would be.