Defining families

Families have a counterpart for the following entity operations: has, hasSet, and hasRelation which match against all entities where those operations would return #!kotlin true.

These operations be joined by three connectives, and, not, or.

Usage

Families don't inline connectives (ex. A or B) since we often want to match many components at once. Thus, we use a tree structure.

Consider three components, A, B, C, let's try to build some families from them.

=== ":octicons-file-code-16: A and B"

```kotlin
family {
    and {
        has<A>()
        has<B>()
    }
}
```
Families default to the and selector, so this is equivalent to the following:

```kotlin
family {
    has<A>()
    has<B>()
}
```

=== ":octicons-file-code-16: A or B or C"

```kotlin
family {
    or {
        has<A>()
        has<B>()
        has<C>()
    }
}
```

=== ":octicons-file-code-16: (A or B) and not C"

```kotlin
family {
    or {
        has<A>()
        has<B>()
    }
    not {
        has<C>()
    }
}
```

=== ":octicons-file-code-16: (A or B) and not (child of C)"

```kotlin
family {
    or {
        has<A>()
        has<B>()
    }
    not {
        and {
            hasRelation<ChildOf?, C?>()
        }
    }
}
```

Getting matched entities

Once created, a family can check if an entity matches it with #!kotlin entity in family // Boolean. More importantly, we can now use them in our systems for fast pattern matching in queries.