Unfolders accepts a list of primitive, processing, or stateful unfolders.

BaseUnfoldState implements UnfoldState, but returns an error for every callback possible.

Expander supports the creation of an UnfoldState for handling the unfolding into the current value.

IsZeroer interface allows custom types to be reported as empty.

UnfoldCtx provides access to the shared unfolding stack.

UnfoldState defines a custom user defined unfolder.