Implement the zip.select function and assorted predicates

[ognen]

We need a way to select one or more elements in the application state given a starting location; also we need a way to specify such a selector to be used in ways we use CSS selectors or xpath queries.

The trick clojure.data.xml is using is well suited here.

• Implement the function

const select: (...predicates) => location => List<locations>

and place in src/zip/index.js

The function is in curried form. It expects a variable arg-set of predicates that is used to select/filter starting from the current location.

Each predicate can be:

• a 'string' which is interpreted as descending into a property. The property should have an element (or child elements)
• an array of strings which is interpreted as the predicate ofKind
• a function returning a list of locations
• a predicate function used to filter out nodes

The system should be identical to the one in clojure.

In addition to the select function, a set of built-in predicates need to be provided:

• ancestors a list of the location's ancestors; nearest parent first
• descendants, a list of all descendants, depth-first, right-to-left
• children(collection) returns a list of the location's children. if a collection is provided it will list only the children in that collection
• ofKind(kind) a predicate function which will return true if the location points to an element the given kind

[ognen]

A sample use case for the function:

// A tab navigation element containing a list of scenes, of which only one can be active at a time 
{
  'kind': 'tab-navigation',
  '@@girders-elements/children': 'scenes',
  'scenes': [
    {
      kind: 'scene',
      id: 1,
      active: true
    },
    {
      kind: 'scene',
      id: 2
    }
  ]
}


// essentially, dispatching 'select' with sceneId = someId on 'tab-navigation' will deactivate all scenes except the selected one
updates.register(['tab-navigation'], nav => {
  // thread  the 'select' action to all children of kind scene where the id is not the sceneId from the action
  nav.thread('select', action => select(children, kindOf('scene'), not(propEq('id', action.sceneId)), 'deactivate');
  // thread the same action to all children of kind scene where action.sceneId === id 
  nav.thread('select', action => select(children, kindOf('scene'), propEq('id', action.sceneId)))), 'activate');
}

// finally the receiving actions
update.register('scene', scene => {
  scene.register('deactivate', s => s.set('active', false));
  scene.register('activate', s => s.set('active', true));
});