Should probably implement add, mul, etc. as objects that can be applied to one or more arguments.

[nikololiahim]

As this example from here suggests:

[r] > circle
  mul 2 3.14 r > perimeter
  mul 3.14 r r > area

[eyihluyc]

There are (at least) two approaches:

1. 'xslt magic':
   For example, the program

[r] > circle
  r.mul 2 3.14 > circumference

with XML representation

<o name="circle">
  <o name="r"/>
  <o base=".mul" name="circumference">
      <o base="r"/>
      <o base="int" data="int">2</o>
      <o base="float" data="float">3.14</o>
  </o>
</o>

is preprocessed to yield

<o name="circle">
  <o name="r"/>
  <o base=".mul" name="circumference">
      <o base=".mul"
          <o base="r"/>
          <o base="int" data="int">2</o>
      </o>
      <o base="float" data="float">3.14</o>
  </o>
</o>

and nothing is to be changed in python runtime.
Probably, this is an easier alternative, and the idea would be that addition/multiplication/conjunction/disjunction are binary operations and support of multiple arguments is rather syntactic sugar.

2. NumberOperation for .add and .mul (as well as yet non-existent .and and .or for Boolean) gets varargs (or some variation of it, for we would need to forbid 0 arguments) as input.
   This approach seems to be another viable response to the mentioned example. Moreover, there exist other atoms that require varargs (e.g. Sprintf)