On Friday, July 4, 2014 2:20:07 AM UTC+2, Matthew wrote:
>
> This is easier if we stop automatic evaluation on classes. I usually
> propose that the classes like `Add` do no construction logic while paired
> functions like `add` take on all of the construction logic. Then you can
> create patterns like Add(oo, 'x') without fear that they will change to
> something else.
>
>
That is an interesting idea. Maybe no SymPy object should overload the
__new__ constructor?
Mathematica uses attributes to define some automatic evaluations, for
example "Flat", have a look at this example:
In[1]:= f[a, b, f[c, d, e]]
Out[1]= f[a, b, f[c, d, e]]
In[2]:= SetAttributes[f, Flat]
In[3]:= f[a, b, f[c, d, e]]
Out[3]= f[a, b, c, d, e]
This could be emulated by putting a static variable *flat* in *Expr*:
class Expr(Basic):
...
flat = False
class Add(...):
...
flat = True
Whenever flat is True, flattening automatically happens upon construction.
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