code: func (options *Options) evalBlock(ctx interface{}, data *DataFrame, key interface{}) string {
  	result := ""
  
  	if block := options.eval.curBlock(); (block != nil) && (block.Program != nil) {
  		result = options.eval.evalProgram(block.Program, ctx, data, key)
  	}
  
  	return result
  }
docs: //
  // Evaluation
  //
  // evalBlock evaluates block with given context, private data and iteration key