@Override
  public String getExprString() {
    // Get the children expr strings
    String[] childrenExprStrings = new String[children.size()];
    for (int i = 0; i < childrenExprStrings.length; i++) {
      childrenExprStrings[i] = children.get(i).getExprString();
    }

    return genericUDF.getDisplayString(childrenExprStrings);
  }
This class uses a writableObjectInspector rather than a TypeInfo to store
the canonical type information for this NodeDesc.
ql/src/java/org/apache/hadoop/hive/ql/plan/ExprNodeGenericFuncDesc.java