[GiNaC-devel] assignments in ginsh

[Richard B. Kreckel]

Hi,

The behavior of ginsh w.r.t. recursive variable assignment has silently 
changed in GiNaC 1.4.4 (eaa0370a). Before, we got:
 > a=3+x:
 > x=2:
 > a;
5

Now, we get:
 > a=3+x:
 > x=2:
 > a;
3+x

It may be worth pointing out that in both cases, one gets:
 > x=2:
 > a=3+x:
 > a;
5

The old behavior can be easily restored (patch attached). Should we?

Pros:
-----
Ginsh isn't a real programming language - it has a global namespace 
without scoping. Under these circumstances, it seems natural to think of 
assignments as occurring in every variable defined before and after. 
(There is even an example in the tutorial which is now wrong; search for 
"x=2".)

Cons:
-----
This is not how it works in C++. There, we have:
     ex x = symbol("x");
     ex a = 3+x;
     x = 2;
     cout << a << endl;  // prints 3+x, not 5

I am inclined to restore the old behavior, but it may be that someone 
has other thoughts. Or, maybe it is totally unimportant?

Any comments?

All my best,
    -richard.
-- 
Richard B. Kreckel
<https://in.terlu.de/~kreckel/>
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