doc/tutorial/basics/2_types/05_types.txt

cue eval types.cue
cmp stdout expect-stdout-cue

-- frontmatter.toml --
title = "Type Hierarchy"

-- text.md --
CUE defines the following type hierarchy

```
  null  bool  string  bytes  number  struct  list
                             /   \
                           int  float
```
In addition, CUE defines the values
bottom, or error, (denoted `_|_`)
that is an instance of all types and
top, or any, (denoted `_`) of which all types are an instance.

Note how we use the terms types and values interchangeably.
CUE does not distinguish between types and values.
The term "type" merely refers to the kind of a value,
which may or may not be a concrete instance.

In the example, `point` defines an arbitrary point, while `xaxis` and `yaxis`
define the points on the respective lines.
We say that `point`, `xaxis`, and `yaxis` are incomplete,
as they do not specify a specific point.
Incomplete values cannot be represented as JSON,
as it can only represent concrete values.

The only concrete point is `origin`.
The `origin` is defined to be both on the x-axis and y-axis, which means it
must be at `0, 0`.
Here we see constraints in action:
`origin` evalutes to `0, 0`, even though we did not specify its coordinates
explicitly.

-- types.cue --
point: {
    x: number
    y: number
}

xaxis: point
xaxis x: 0

yaxis: point
yaxis y: 0

origin: xaxis & yaxis

-- expect-stdout-cue --
point: {
    x: number
    y: number
}
xaxis: {
    x: 0
    y: number
}
yaxis: {
    x: number
    y: 0
}
origin: {
    x: 0
    y: 0
}