elliptical/doc/advanced/visit.md

Interactive natural-language interfaces

# Implementing Visit

Every now and then, you need to create a phrase that manipulates options
manually, rather than simply describing a grammar with elements.
This is the lowest-level elliptical feature, and most people will never
need to use it.

```js
visit: (
  option: Option,
  element: Element
  traverse: (element: Element, option: Option) => Iterable<Option>
) => Iterable<Option>
```

The `visit` function will only be called if `describe` does not exist.
If it needs to parse children, it can do so with the `traverse` function
which is passed as the third argument.

```js
const MyPhrase = {
  visit (option, {props, children}, traverse) {
    console.log('props', props, 'option', option)
    return traverse(children[0])
  }
}
```