- maybe-fold kons nil maybeprocedure
- either-fold kons nil eitherprocedure
If maybe/either is a Just/Right, kons is invoked on the values of its payload and the additional value nil and the result is returned; otherwise, nil is returned.
If maybe/either is a Just/Right, kons is invoked on the values of its payload and the additional value nil and the result is returned; otherwise, nil is returned.