[Scilab-users] Variable scope in Scilab

[Stéphane Mottelet]

Hi all,

In Scilab the scope of variables is quite permissive but even in Julia 
(really strict rules) we can have the following behavior:

function y=f(x)
  y=x+a;
end

a=1;
f(2)
a=2;
f(3)

-> a=1;

--> f(2)
  ans  =

    3.

--> a=2;

--> f(3)
  ans  =

    5.

Yesterday afternoon I was my students for a Scilab beginners tutorial, 
and by accident one of them had "x" defined before in the main workspace 
and tried to call f without arguments. I reproduce the experiment here 
by explicitely defining x before the call:

x=1;
f

--> x=1;

--> f
  ans  =

    3.

Allowing the function inner scope to see variables of the outer scope is 
one thing, you may or may not agree this is not the point here, but 
allowing to call f without arguments just because the formal input 
parameter has the same symbol as an outer scope symbol is another thing. 
I knew this was possible even if i never used such a feature, but my 
students were so puzzled by this, particularly those who already learned 
other low-level languages, that I decided to propose the suppression of 
this, that I consider as a serious potential source of many bugs. Don't 
tell me that this would break some user code because I frankly have no 
consideration for this kind of crappy shortcut and, sorry if it may 
sound rude, for programmers who use it...

S.

-- 
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