Fold nodes of a tree level to their ordinal in depth-first pre-order.
A function of the type:
<A, E = never, R = never>( _: TreeF<A, number>): Effect.Effect<number, E, R> Copy
<A, E = never, R = never>( _: TreeF<A, number>): Effect.Effect<number, E, R>
Fold nodes of a tree level to their ordinal in depth-first pre-order.
A function of the type: