The unique location of a Tree in a Forest.

Describes which tree to step inside plus the TreePath to navigate inside that tree.

Represented as a tuple to simplify pattern matching and enable using it as a comparable key.

Instead of working with that List directly, I recommend using the helpers here to create and operate on these paths.

Construct a ForestPath from the treeIndex and pathIntoTreeAtIndex

import Tree
import Tree.Path
import Forest.Navigate


[ Tree.singleton 0
, Tree.singleton 1
]
    |> Forest.Navigate.to (Forest.Path.fromIndex 1 Tree.Path.atTrunk)
--> Just (Tree.singleton 1)

Which tree to step inside in a Forest

The TreePath to navigate inside the tree at the treeIndex.

The path to its ...th child from there.

import Tree.Path


Forest.Path.fromIndex 1 Tree.Path.atTrunk
    |> Forest.Path.toChild 4
    |> Forest.Path.toChild 1
    |> Forest.Path.toChild 8
--> Forest.Path.fromIndex 1 (Tree.Path.follow [ 4, 1, 8 ])

At the first tree:

1. Take the branch at index 4

2. Then take its branch at index 1

3. Its child at index 8 is where the navigation should end