Deciding on what kinds of data to support

There are at least three categories of data types to consider in your language design. The first one is atomic, scalar primitive types, often called first-class data types. The second is composite or container types, which are capable of holding and organizing collections of values. The third (which may be variants of the first or second categories) is application domain-specific types. You should formulate a plan for each of these categories.

Atomic types

Atomic types are generally built-in and immutable. You don't modify existing values; you just use operators to create new values. Pretty much all languages have built-in types for numbers and a few additional types. A Boolean type, null type, and maybe a string type are common atomics, but there are others.

You decide just how complicated to get with atomics: how many different machine representations of integers and real numbers do you need? Some languages might provide a single...