[Scilab-users] Awkward behavior of error handling <= for a too big number of inputs

[Federico Miyara]

Stéphane,

Thanks for the explanation.

I find it already dangerous that a function be aware of the calling 
level variables of equal name. But allowing so even for input arguments 
is too much. I agree with you.

Generally, variables inside a function are bound or dummy variables. Any 
other variable or parameter to be collected from the context should be 
passed through the arguments. This is much safer and better programming 
style, I think, since everybody is aware of the previously assigned 
variables required to be to be able to apply the function.

I guess a macro designed for general use will never ever exploit this 
feature...

Regards,

Federico


On 07/02/2020 05:14, Stéphane Mottelet wrote:
>
> Here is the explanation : when you write a macro prototype, e.g. like 
> this one
>
> function foo(x)
>
> endfunction
>
> when you call it with too many arguments, then the error always 
> triggered by the parser.
>
> When you call the function with not enough arguments, then the 
> variable scope takes precedence. For example the following is legal:
>
> x=1
> foo()
>
> i.e. even when not enough input arguments, then the call may be OK, 
> but hopefully argn(2) will have the correct value, i.e. 0 above. That 
> is the reason why the parser always allow the call when there is not 
> enough arguments, leaving the body of the macro do the verification, 
> if necessary.
>
> To me this kind of scoping is always source of error and side effects. 
> Accessing the calling context variable by value is OK, but that formal 
> arguments may be asssigned like this id very prone to errors, at least 
> for beginners.
>
> S.
>
> Le 07/02/2020 à 06:09, Federico Miyara a écrit :
>>
>> Samuel,
>>
>> Thanks for clarifying. I have still a doubt regardihng the hard 
>> coding. Functions such as cos and abs, which are
>> primitives, do declare an excess of arguments:
>>
>> --> cos(6,7)
>>
>> cos: Wrong number of input argument(s): 1 expected.
>>
>> Is the behavior different for primitives or they have a way of 
>> bypassing the hard-coded detection?
>>
>> Regards,
>>
>> Federico Miyara
>>
>>
>> On 06/02/2020 18:35, Samuel Gougeon wrote:
>>> Hello Federico,
>>>
>>> Le 06/02/2020 à 22:04, Federico Miyara a écrit :
>>>>
>>>> Dear All,
>>>>
>>>> I'm trying to cast an error message for a function
>>>>
>>>> The test and message are
>>>>
>>>> if argn(2)<>1
>>>>    t1 = "%s: Wrong number of input arguments: %d expected.\n"
>>>>    t2 = "Si"
>>>> error(msprintf(gettext(t1),t2,1));
>>>> end
>>>
>>>
>>> Please pay attention to avoid separating the gettext() call from its 
>>> first literal argument. The reason is described with details in the 
>>> gettext() page. So, to abstract, writting both the following is not 
>>> fully equivalent:
>>>
>>> t1 = "%s: Wrong number of input arguments: %d expected.\n"
>>> gettext(t1)
>>>
>>> and
>>>
>>> gettext("%s: Wrong number of input arguments: %d expected.\n")
>>>
>>>
>>> Here, this separation has no consequence, because you are using a 
>>> standard message that already has a translation in Scilab. But for 
>>> custom messages as in a toolbox, gettext() could here fail finding 
>>> the translation.
>>>
>>>>
>>>> The function has only one argument, so if invoked with 0 or more 
>>>> than one argument, the message should be the same. With 0 arguments 
>>>> I get:
>>>>
>>>>
>>>> --> y = Si()
>>>>
>>>>    0.
>>>> at line    26 of function Si ( D:\work_scilab\Si.sci line 26 )
>>>>
>>>> Si: Wrong number of input arguments: 1 expected.
>>>>
>>>>
>>>> This is the correct and expected message. However, with 2 arguments 
>>>> I get
>>>>
>>>>
>>>> --> y = Si(1,2)
>>>>
>>>> Wrong number of input arguments.
>>>>
>>>>
>>>> This error seems to have been trapped before my test, 
>>>
>>>
>>> Yes, this is the case. This is a general features for all macros. 
>>> The detection of a number of input arguments greater than the max 
>>> acceptable by the macro is hard-coded, and stops the execution 
>>> BEFORE "really" calling and entering the macro. This is the very 
>>> first step that must be passed. Afterward, things actually "occur" 
>>> in the macro.
>>>
>>>> the execution is halted and my message doesn't show. I've also 
>>>> tested the function wavwrite, which requires 2 or 3 arguments. With 
>>>> 0 or 1 the message is the expected one, but with 4 or more 
>>>> arguments, I get the same result as in my example.
>>>>
>>>> Seems as if less arguments are handled by the custom error handler, 
>>>> but more than required is handled by sort of a parser.
>>>>
>>>> I think this behavior contradicts the facility of customizing error 
>>>> messages.
>>>
>>> Not really. Only this one, related to an excessive number of inputs. 
>>> Since the number of possible distinct errors is infinite, it's cool. 
>>> Our freedom to customize all other messages is also infinite :-))
>>>
>>>
>>> Regards
>>> Samuel
>>>
>>>
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>>
>>
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> -- 
> Stéphane Mottelet
> Ingénieur de recherche
> EA 4297 Transformations Intégrées de la Matière Renouvelable
> Département Génie des Procédés Industriels
> Sorbonne Universités - Université de Technologie de Compiègne
> CS 60319, 60203 Compiègne cedex
> Tel : +33(0)344234688
> http://www.utc.fr/~mottelet
>
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