> Dan Larson made a nice picture to illustrate this
>
>
> -----     -----     -----     -----     -----
> |   |---->|   |---->|   |---->|   |---->|   |
> | 7 |     | = |     | 5 |     | + |     | 2 |
> |   |<----|   |<----|   |<----|   |<----|   |
> -----     -----     -----     -----     -----

You wouldn't be able to reorganize this in such a way that:

 ----------   ----------
 |        |   |        |
 |    7   |   |    5   |
 ----------   ----------
        V      V
       ----------
       |        |
       |     +  |
       ----------
              V
       ----------
       | display|
       |     =  |
       ----------

Would you?  This way you would be taking the expression and building
an evaluation tree.  Allows for much more complex expressions.  Maybe
this is more like "comp sci" blocks rather than something simple to
teach basics to children.  But it *really* reduces the coding problem.
No block ID codes, no "who's there" problem.  The blocks only have to
talk to adjacent blocks and pass down the result.

Chris