import com.sun.org.apache.xpath.internal.functions.FuncExtFunctionAvailable; //导入依赖的package包/类
/**
 * Compile a built-in XPath function.
 *
 * @param opPos The current position in the m_opMap array.
 *
 * @return reference to {@link com.sun.org.apache.xpath.internal.functions.Function} instance.
 *
 * @throws TransformerException if a error occurs creating the Expression.
 */
Expression compileFunction(int opPos) throws TransformerException
{

  int endFunc = opPos + getOp(opPos + 1) - 1;

  opPos = getFirstChildPos(opPos);

  int funcID = getOp(opPos);

  opPos++;

  if (-1 != funcID)
  {
    Function func = m_functionTable.getFunction(funcID);

    /**
     * It is a trick for function-available. Since the function table is an
     * instance field, insert this table at compilation time for later usage
     */

    if (func instanceof FuncExtFunctionAvailable)
        ((FuncExtFunctionAvailable) func).setFunctionTable(m_functionTable);

    func.postCompileStep(this);

    try
    {
      int i = 0;

      for (int p = opPos; p < endFunc; p = getNextOpPos(p), i++)
      {

        // System.out.println("argPos: "+ p);
        // System.out.println("argCode: "+ m_opMap[p]);
        func.setArg(compile(p), i);
      }

      func.checkNumberArgs(i);
    }
    catch (WrongNumberArgsException wnae)
    {
      java.lang.String name = m_functionTable.getFunctionName(funcID);

      m_errorHandler.fatalError( new TransformerException(
                XSLMessages.createXPATHMessage(XPATHErrorResources.ER_ONLY_ALLOWS,
                    new Object[]{name, wnae.getMessage()}), m_locator));
            //"name + " only allows " + wnae.getMessage() + " arguments", m_locator));
    }

    return func;
  }
  else
  {
    error(XPATHErrorResources.ER_FUNCTION_TOKEN_NOT_FOUND, null);  //"function token not found.");

    return null;
  }
}