Declaring Subtypes Quiz

1. A word is defined as a non-empty string, all of whose characters are printable. Declare a class Word to represent this.

 class Word ^= those x: string :- ~x.empty &
  (forall c::x :- c.isPrintable);

2. Declare a class Fractional to represent real numbers in the range -1 to +1.

 class Fractional ^= those x: real :- -0.0 <=
  x <= 0.0;