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

[Stéphane Mottelet]

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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