An action call within an expression transfers control to the statements within the action body during expression evaluation and temporarily suspends the expression evaluation. If the action has parameters, then their values are copied to the action's formal parameter variables. When the control flow reaches the action's end or the action executes a return statement, control is transferred back to the expression and evaluation continues.

The actual parameters are a comma-separated list of expressions. The entire list is enclosed in parentheses. It forms the set of parameter values that are passed when the action is called. Each expression value is copied to the corresponding parameter variable specified in the action definition's formal parameters, and the expression result type must match the parameter variable's type. The number and order of actual parameters passed by a caller must also match those listed in the action definition's formal parameters.

The action or method being invoked in the expression must return a value. The action's return type becomes the expression result type.