Interface for qBeta module object

Origin: ExpressionGrammar

expAst: obj
   Top:
      print:<
      isEmpty:<
         out B: var Boolean
      eval:<
         out V: var integer
   Node:left:right: Top
      print::
   expNode:left:right: Node:left:right
      eval::
   termNode:left:right: Node:left:right
      eval::
   numberNode:left:right: Node:left:right
      eval::
   digitNode:left:right: Node:left:right
      eval::
   empty: top
      isEmpty::
      eval::
   ind: var integer