[Info-vax] BASIC (and Horizon)

[Dave Froble]

On 1/31/2024 7:29 PM, Arne Vajhøj wrote:
> On 1/31/2024 6:21 PM, Lawrence D'Oliveiro wrote:
>> On Wed, 31 Jan 2024 17:08:44 -0500, Arne Vajhøj wrote:
>>
>>> On 1/31/2024 4:28 PM, Lawrence D'Oliveiro wrote:
>>>
>>>> I have never written a goto in C code (not production code, anyway). These
>>>> days, you need to do so much dynamic allocation, there is nearly always
>>>> some need for cleanup when exiting an inner block anyway, so you can’t
>>>> just jump directly somewhere else first. The overall pattern looks like
>>>> this:
>>>>
>>>>       MyPtr obj = NULL;
>>>>       do /*once*/
>>>>         {
>>>>           ... possible other stuff ...
>>>>           «allocate memory for obj»;
>>>>           if («error occurred»)
>>>>               break;
>>>>           ... possible other stuff using obj ...
>>>>         }
>>>>       while (false);
>>>>       free(obj);
>>>>
>>>> You can confirm, just by inspection, that there is no path out of the
>>>> block that does not pass through the free() call precisely once.
>>>
>>> And the difference compared to:
>>>
>>>        MyPtr obj = NULL;
>>>        ... possible other stuff ...
>>>        «allocate memory for obj»;
>>>        if («error occurred»)
>>>            goto lbl_freeobj;
>>>        ... possible other stuff using obj ...
>>>     lbl_freeobj:
>>>        free(obj);
>>>
>>> are?
>>
>> Nesting.
>
> Goto work fine with nested loops. In fact it is one of the cases
> where it really makes sense.
>
>>           Try to scale up to something like
>>
>> static PyObject * discipline_makedict
>>    (
>>      PyObject * self,
>>      PyObject * args
>>    )
>>    {
>>      PyObject * result = NULL;
>>      PyObject * tempresult = NULL;
>>      br_PyObject * items;
>>      const br_char * msg = NULL;
>>      do /*once*/
>>        {
>>          const bool parsed_ok = PyArg_ParseTuple(args, "Os", &items, &msg);
>>          if (not parsed_ok)
>>              break;
>>          fprintf(stdout, "makedict says: “%s”\n", msg);
>>          if (not PyTuple_Check(items))
>>            {
>>              PyErr_SetString(PyExc_TypeError, "expecting a tuple");
>>              break;
>>            } /*if*/
>>          const ssize_t nr_items = PyTuple_Size(items);
>>          if (PyErr_Occurred())
>>              break;
>>          tempresult = PyDict_New();
>>          if (tempresult == NULL)
>>              break;
>>          for (ssize_t i = 0;;)
>>            {
>>              if (i == nr_items)
>>                  break;
>>              br_PyObject * const item = PyTuple_GetItem(items, i);
>>              if (item == NULL)
>>                  break;
>>              if (not PyTuple_Check(item) or PyTuple_Size(item) != 2)
>>                {
>>                  PyErr_SetString(PyExc_TypeError, "expecting a 2-tuple");
>>                  break;
>>                } /*if*/
>>              br_PyObject * const first = PyTuple_GetItem(item, 0);
>>              if (first == NULL)
>>                  break;
>>              br_PyObject * const second = PyTuple_GetItem(item, 1);
>>              if (second == NULL)
>>                  break;
>>              if (first == (PyObject *)&ExceptMe_type or second == (PyObject
>> *)&ExceptMe_type)
>>                {
>>                  PyErr_SetString(PyExc_ValueError, "ExceptMe object found");
>>                  break;
>>                } /*if*/
>>              if (PyDict_SetItem(tempresult, first, second) < 0)
>>                  break;
>>              ++i;
>>            } /*for*/
>>          if (PyErr_Occurred())
>>              break;
>>        /* all done */
>>          result = tempresult;
>>          tempresult = NULL; /* so I don’t dispose of it yet */
>>        }
>>      while (false);
>>      Py_XDECREF(tempresult);
>>      return
>>          result;
>>    } /*discipline_makedict*/
>
> That code would look a lot cleaner if the do while(false) loop got
> removed and the relevant breaks got replaced by goto's.
>
> A well named goto label is much more informative than a plain break.
>
>> More details here
>> <https://gitlab.com/ldo/a_structured_discipline_of_programming/>.
>
> Truly bad design.
>
> All the code examples would look better with the do while(false) loops
> removed and appropriate goto's.
>
> Arne
>

It's called do whatever to avoid a goto, and it can be very bad ...

-- 
David Froble                       Tel: 724-529-0450
Dave Froble Enterprises, Inc.      E-Mail: davef at tsoft-inc.com
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