quiz about symbolic manipulation

[Michele Simionato]

bokr at oz.net (Bengt Richter) wrote in message news:<atasp6$loc$0 at 216.39.172.122>...
> >
> >In[1]:= square[square[x+y]+z]+square[x+w]/.square[x_] -> x^2
> >
> >               2                      2
> >Out[1]= (w + x)  + (z + square[x + y])
>          ^^^^^^^^   ^^^^^^^^^^^^^^^^^^^^
>             |                   |
>             +-----------+       |
>                         |       |
>                      vvvvvvvv   |
> [2] "((x+y)**2+z)**2+(x+w)**2"  |
>      ^^^^^^^^^^^^^^^            |
>             |                   |
>             +-------------------+
> 
> What am I missing?
 
The "/." substitution operator of Mathematica does not work
recursively:
you see that the result still contain the expression square[x+y] and
that
you should apply "/." again to get rid of this second square.
Of course, as Carl pointed out, you could use the "//." operator, but
this
is not the point: I would like to do this in Python. My example
(perhaps
not too happily chosen) simply wanted to point out the need for a
recursive
algorithm. Still I think the solution should be not too difficult
using the
compiler module, but I have problems in understanding this module
since the documentation is still rather poor and not so clear (to me
at least).
Bye,

                            Michele