One.java

package fj.data.fingertrees;

import fj.F;
import fj.P;
import fj.P2;
import fj.P3;
import fj.Show;
import fj.data.Option;
import fj.data.Stream;

import static fj.data.Option.none;

/**
 * A single-element prefix or suffix of a finger tree.
 */
public final class One<V, A> extends Digit<V, A> {
  private final A a;

  One(final Measured<V, A> m, final A a) {
    super(m);
    this.a = a;
  }

  public <B> B foldRight(final F<A, F<B, B>> aff, final B z) {
    return aff.f(a).f(z);
  }

  public <B> B foldLeft(final F<B, F<A, B>> bff, final B z) {
    return bff.f(z).f(a);
  }

  @Override public <B> B match(
      final F<One<V, A>, B> one, final F<Two<V, A>, B> two, final F<Three<V, A>, B> three,
      final F<Four<V, A>, B> four) {
    return one.f(this);
  }

  /**
   * Returns the single element in this digit.
   *
   * @return the single element in this digit.
   */
  public A value() {
    return a;
  }

  @Override P3<Option<Digit<V, A>>, A, Option<Digit<V, A>>> split1(final F<V, Boolean> predicate, final V acc) {
    return P.p(none(), a, none());
  }

  @Override public P2<Integer, A> lookup(final F<V, Integer> o, final int i) {
    return P.p(i, a);
  }

    @Override
    public int length() {
        return 1;
    }

  public String toString() {
    return Show.digitShow(Show.<V>anyShow(), Show.<A>anyShow()).showS(this);
  }

  public Stream<A> toStream() {
    return Stream.single(a);
  }

}