Hyperapp V2 actions state lens

lens.js

/*

This is variation of `squirrel` and `namespace` approaches
https://gist.github.com/zaceno/0d7c62be81a845857e755c1378b7dbff
https://gist.github.com/sergey-shpak/5817bf146cb970bc4e259aef71b89ef4

Simplifies Hyperapp#v2 actions work with deeply nested state
(updated to support returned actions, parameterized actions)

Usage examples:

```
const actions = {
  update: (property, value) => value
}

export default {
  update: lens(['deeply','nested','property'], actions.update)
}
```

and then call the action

```
import actions from './path/to/actions'

<div onClick={[ actions.update, "new value" ]} />
```

*/

export const lens = (path, cb) =>
  path.reduceRight((fn, key) => (obj, ...args) => {
    const result = fn(obj[key], ...args)
    return (Array.isArray(result) || typeof result == 'function')
      ? result : { ...obj, [key]: result }
  }, cb)