9.4 Summary

In this chapter, we discussed types that are not classes:

• A singleton type is a type whose only member is one particular instance. An example of creating a singleton type is:

singleton(#f);

• A union type is a type whose members include all the members of one or more base types. An example of creating a union type is:

type-union(singleton(#f), <integer>);

• A limited type is a type that is a more restricted version of its base type. For example, a limited-integer type is based on <integer>, but has a given minimum or maximum value:

limited(<integer>, min: 0);

Another example of a limited type is a limited-collection type, which is a collection type that specifies the type of elements, and/or the size of the collection:

limited(<vector>, of: <integer>, size: 3);