code: def expressionToAST(ex):
      
      return ASTNode(ex.astType, ex.astKind, ex.value,
                     [expressionToAST(c) for c in ex.children])
docs: Take an expression tree made out of expressions.ExpressionNode,
      and convert to an AST tree.
  
      This is necessary as ExpressionNode overrides many methods to act
      like a number.