func (expr *UnaryOpExpression) Value(device datalayer.Device) (cloudvar.CloudVarValue, error) {
switch expr.operation {
case NOT:
val, err := expr.operand.Value(device)
if err != nil {
return nil, err
}
valBool, ok := val.(bool)
if !ok {
return nil, fmt.Errorf("NOT operand must evaluate to boolean")
}
return !valBool, nil
case HAS:
propExpr, ok := expr.operand.(*PropertyExpression)
if !ok {
return nil, fmt.Errorf("HAS operand must be a variable reference")
}
_, err := device.LookupVarDef(propExpr.property)
return (err == nil), nil
default:
return false, fmt.Errorf("Unexpected unary operation")
}
}
