Primitive Types
- num
- bool
- str

```
fact(x) = ? (x <= 1) 1 : f(x-1) * x
> lambda
fact(5) == 120
> True
```

Ordered collections.
| Name | Homogeneous | Fixed Size | Unique |
|---|---|---|---|
| Collection | No | No | No |
| List |  Yes | No | No |
| Array | Yes | Yes | No |
| Group | No | Yes | No |
| Set | Yes | No | Yes |
| Perm | Yes | Yes | Yes |