1. Parameters and World-level methods
Alice

2. Our Dragon world
In the last class, we created methods for the dragon to take off and fly.

3. Storyboards
Recall how we had the dragon takeOff, and how we had it fly.
Dragon.takeOff
Do together
dragon move up 1 meter
dragon flap its wings
Dragon.fly
Do together
dragon move forward 1 meter
dragon flap its wings
Note that we would need very similar methods to get the dragon to land (by flying down) or to fly in other directions

4. A Better Solution
Multiple versions of very similar code seems a bit tedious. The only things that change is the direction the dragon is to fly.
A better solution is to write a more flexible method.

5. Parameters
Built-in methods provide flexibility by providing parameters such as distance and direction.
Parameters allow you to pass in values (arguments).
Example
Parameters: direction, distance, duration
Arguments: left, 0.05 revolutions, 0.5 seconds

6. Kinds of Parameters
Alice provides several kinds of parameters that can be used in your own methods.

7. The storyboard In this example, we can write just one method and
use a parameter to specify:
which direction the dragon is to fly.
Dragon.flyInAnyDirection
Parameter: whichDirection
Do together
dragon move in whichDirection
dragon flap its wings

8. Demo Concepts illustrated
Enter name and select the type of each parameter
whichDirection is a Direction parameter
A parameter acts as a placeholder in the instruction
Arguments are passed to the parameter in the call to the method

9. A Number parameter
Add a Number parameter to specify the distance the dragon travels as it is flying.
Note that the call to the method must now include an argument for the distance.
Traditional Lecture: Demo adding a number parameter for the height of the jump.
Active learning: Students add the number parameter and revise the statement to call the method.

10. World-level methods It is also possible to create world-level methods
These are used when there are references to multiple objects in the world

11. Example Consider our dragon world The dragon has taken off
Now it must fly to the princess.
Such a method will involve 2 objects: the dragon and the princess

12. Demo: Starting a new method
First, to associate the new method with the World
select the World tile in the Object Tree
select the methods tab in the details area
click on the "create new method" button

13. Demo
Creating the flyToPrincess method

14. Assignment
Read Chapter 4-1 and 4-2
World-level methods
Parameters