Data Types

Like other Lisps, it is data objects that are typed, not variables. Any variable can have any object as its value. Although it is possible to declare the type of object which is bound to a variable, but usually it is only advisory information to the compiler to generate faster code. Numbers are represented as immediate values in pointers and all the others are represented by objects referenced by pointers.

In the implementation of Sun4, a pointer or a number is represented by a long word as depicted in fig.2. Two bits at LSB of a pointer are used as tag bits to discriminate between a pointer, an integer, and a float. Since a pointer's tags are all zero and it can use all 32 bits for addressing an object, EusLisp can utilize up to 4GB of process address space.

Figure 2: Pointer and Immediate Value