I have an implementation of the "[Little
Scheme](https://mitpress.mit.edu/9780262560993/the-little-schemer/)" educational programming language written in D, [here](https://github.com/jwatson-CO-edu/SPARROW)".
It has many problems, but the one I want to solve first is the
size of the "atoms" (units of data).
`Atom` is a struct that has fields for every possible type of
data that the language supports. This means that a bool `Atom`
unnecessarily takes up space in memory with fields for number,
string, structure, etc.
Here is the
[definition](https://github.com/jwatson-CO-edu/SPARROW/blob/main/lil_schemer.d#L55):
```d
enum F_Type{
CONS, // Cons pair
STRN, // String/Symbol
NMBR, // Number
EROR, // Error object
BOOL, // Boolean value
FUNC, // Function
}
struct Atom{
F_Type kind; // ---------------- What kind of atom this is
Atom* car; // ----------------- Left `Atom` Pointer
Atom* cdr; // ----------------- Right `Atom` Pointer
double num; // ----------------- Number value
string str; // ----------------- String value, D-string
underlies
bool bul; // ----------------- Boolean value
F_Error err = F_Error.NOVALUE; // Error code
}
```
Question:
**Where do I begin my consolidation of space within `Atom`? Do I
use unions or variants?**