content: package com.alibaba.qlexpress4.runtime.instruction;
  
  import com.alibaba.qlexpress4.QLOptions;
  import com.alibaba.qlexpress4.exception.ErrorReporter;
  import com.alibaba.qlexpress4.runtime.QContext;
  import com.alibaba.qlexpress4.runtime.QResult;
  import java.util.function.Consumer;
  
  /**
   * Instruction Specification:
   *
   * Operation: What does it do?
   * Input: How many stack element it consumes? and their means
   * Output: How many stack element it push back? and their means
   * <p>
   * Author: DQinYuan
   */
  public abstract class QLInstruction {
      
      protected final ErrorReporter errorReporter;
      
      public QLInstruction(ErrorReporter errorReporter) {
          this.errorReporter = errorReporter;
      }
      
      public abstract QResult execute(QContext qContext, QLOptions qlOptions);
      
      /**
       * @return input size
       */
      public abstract int stackInput();
      
      /**
       * @return output size
       */
      public abstract int stackOutput();
      
      public abstract void println(int index, int depth, Consumer<String> debug);
      
      public ErrorReporter getErrorReporter() {
          return errorReporter;
      }
  }
  