4. Controlling Conditional Execution

So far we have controlled how our world should execute by checking whether the distance between two objects is greater than a certain amount -- or not. Now we'd like to play around with other ways we can control conditional execution -- other forms of Boolean expressions that evaluate to either true or false. For the sake of efficiency, we may not do things that necessarily make much sense in our particular world... but we can still get an idea of what our options are.

There are a lot of functions that return Boolean values (true or false) under the World object, functions. Scroll down to the second section called "math".

Practice Activities:

Changing Distance:

1. Try to change the distance where the Angel will respond and approach the Egyptian to be within (less than) 8 meters instead of 5 meters (you don't have to change the blue circle -- we just had that to make the original boundary "visible" to you). Save your World as M8-PA1-AngelSometimes-YourName.a2w
2. Try to change the boolean expression so that the Angel will approach the Egyptian only when he is more than 6 meters away -- otherwise he should say "You are close enough, just yell". (Hint: this will involve both changing the Boolean expression and the instruction in the Else portion of the if/else statement). Save your World as M8-PA2-AngelSometimes-YourName.a2w

Checking for an exact Distance:

1. Suppose you want the Angel only to approach when he is exactly 2 meters away, and otherwise he should say "Sorry, try again!". Hint: In Alice and most computer languages -- to check if something is equal to something else we write (something == somethingElse). Save your World as M8-PA3-AngelSometimes-YourName.a2w
2. How about if he should only approach when he is NOT exactly 2 meters away, and otherwise say "Sorry, try again!". (Hint: in Alice and most computer languages, the "!" means "not". So to check for something to be not equal to something else we write (something != somethingElse). Save your World as M8-PA4-AngelSometimes-YourName.a2w

[Q8.4.1]: What if we wanted to have the Angel approach the Egyptian only in the situation where the Egyptian is less than 2 meters tall, and otherwise have the Angel say "Sorry, try again". Suppose you have the code from the last example. What would you change the Boolean expression to be?

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