Predicates

A function that produces a boolean (true or false) value

String Predicates

Non-numeric types also have predicates.

For example, we can tell if two strings are the same:

(string=? “pearls” “gems”) ⇒ false

(string=? “pearls” “pearls”) ⇒ true

we can also compare the lexicographical order or two strings

(string<? “pearls” “swine”) ⇒ true

(string<? “pearls” “pasta”) ⇒ false

(string≤? “pearls” “pearls”) ⇒ true

Conditional Expressions

Sometimes expression can take more than one value

• Conditional expressions use the special form cond.

• Each argument is a question/answer pair

• The question is a boolean expression

• The answer is a possible value of the conditional expression