# SoftBank Robotics documentation What's new in NAOqi 2.8?

# ALExpressionWatcher API

NAOqi Core - Overview | API | ExpressionObject API

Namespace : AL

## Method list

class `ALExpressionWatcher`
  - Methods for ALExpressionWatcher:
    - `ALExpressionWatcher::add`

## Methods

ExpressionObject `ALExpressionWatcher::``add`(const std::string& expression, const int& report_mode)

  Adds a condition expression to ALExpressionWatcher engine.

  Return an ExpressionObject that embeds some methods and a qi::Signal triggered each time the condition expression is valid with condition expression value.

  Note: this ExpressionObject should be kept alive as a variable otherwise the expression is not watched anymore. For further details, see: Example.

  Parameters: | expression – condition expression in Conditions expression language. report_mode – { REPORT_CHANGE = 0, REPORT_EDGE = 1, REPORT_EDGE_TRUE = 2 }. For further details see: Report modes.
  Returns: | Correspondig ExpressionObject.

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