Inequalities

Sometimes we want to ask questions about data. For example, is x greater than y? Is one string equal to another? These questions can’t be answered with Numbers. Instead, they are answered with a new data type called a Boolean.
video games use Booleans for many things: asking when a player’s health is equal to zero, whether two characters are close enough to bump into one another, or if a character’s coordinates put it off the edge of the screen.
A Boolean value is either true or false. Unlike Numbers, Strings, and Images, Booleans have only two possible values.
You already know some functions that produce Booleans, such as < and >! Our programming language has them, too: (< 3 4), (> 10 2), and (= -10 19).
We also have ways of writing Compound Inequalities, so we can ask more complicated questions using the and and or functions.
- (and (> 3 4) (< 10 2)) translates to "three is greater than four and ten is less than two". This will evaluate to false, since the and function requires that both sub-expressions be true.
- (or (> 3 4) (< 10 2)), which translates to "three is greater than four or ten is less than two". This will evaluate to true, since the or function only requires that one sub-expression be true.
The Circles of Evaluation work the same way with Booleans that they do with Numbers, Strings and Images:
and
>
3 4
<
10 2
(and (> 3 4) (< 10 2))

or
>
3 4
<
10 2
(or (> 3 4) (< 10 2))

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