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158 lines (131 loc) · 4.34 KB
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package fj.data;
import fj.*;
import static fj.Bottom.error;
import static fj.Monoid.intAdditionMonoid;
import static fj.data.fingertrees.FingerTree.measured;
import fj.data.fingertrees.FingerTree;
import fj.data.fingertrees.MakeTree;
import fj.data.fingertrees.Measured;
/**
* Provides an immutable finite sequence, implemented as a finger tree. This structure gives O(1) access to
* the head and tail, as well as O(log n) random access and concatenation of sequences.
*/
public final class Seq<A> {
private static final Measured<Integer, Object> ELEM_MEASURED = measured(intAdditionMonoid, Function.constant(1));
private static final MakeTree<Integer, Object> MK_TREE = FingerTree.mkTree(ELEM_MEASURED);
private static final Seq<Object> EMPTY = new Seq<Object>(MK_TREE.empty());
@SuppressWarnings("unchecked")
private static <A> MakeTree<Integer, A> mkTree() {
return (MakeTree<Integer, A>) MK_TREE;
}
private final FingerTree<Integer, A> ftree;
private Seq(final FingerTree<Integer, A> ftree) {
this.ftree = ftree;
}
@SuppressWarnings("unchecked")
private static <A> Measured<Integer, A> elemMeasured() {
return (Measured<Integer, A>) ELEM_MEASURED;
}
/**
* The empty sequence.
*
* @return A sequence with no elements.
*/
@SuppressWarnings("unchecked")
public static <A> Seq<A> empty() {
return (Seq<A>) EMPTY;
}
@Override
public boolean equals(Object other) {
return Equal.shallowEqualsO(this, other).orSome(P.lazy(u -> Equal.seqEqual(Equal.<A>anyEqual()).eq(this, (Seq<A>) other)));
}
/**
* A singleton sequence.
*
* @param a The single element in the sequence.
* @return A new sequence with the given element in it.
*/
public static <A> Seq<A> single(final A a) {
return new Seq<A>(Seq.<A>mkTree().single(a));
}
public static <A>Seq<A> seq(final A... as) {
return seq(List.list(as));
}
public static <A>Seq<A> seq(final List<A> list) {
return list.foldLeft((b, a) -> b.snoc(a), Seq.<A>empty());
}
/**
* Inserts the given element at the front of this sequence.
*
* @param a An element to insert at the front of this sequence.
* @return A new sequence with the given element at the front.
*/
public Seq<A> cons(final A a) {
return new Seq<A>(ftree.cons(a));
}
/**
* Inserts the given element at the end of this sequence.
*
* @param a An element to insert at the end of this sequence.
* @return A new sequence with the given element at the end.
*/
public Seq<A> snoc(final A a) {
return new Seq<A>(ftree.snoc(a));
}
public Stream<A> toStream() {
return ftree.foldLeft((b, a) -> b.cons(a), Stream.<A>nil()).reverse();
}
@Override
public String toString() {
return Show.seqShow(Show.<A>anyShow()).showS(this);
}
/**
* Appends the given sequence to this sequence.
*
* @param as A sequence to append to this one.
* @return A new sequence with the given sequence appended to this one.
*/
public Seq<A> append(final Seq<A> as) {
return new Seq<A>(ftree.append(as.ftree));
}
/**
* Checks if this is the empty sequence.
*
* @return True if this sequence is empty, otherwise false.
*/
public boolean isEmpty() {
return ftree.isEmpty();
}
/**
* Returns the number of elements in this sequence.
*
* @return the number of elements in this sequence.
*/
public int length() {
return ftree.measure();
}
/**
* Returns the element at the given index.
*
* @param i The index of the element to return.
* @return The element at the given index, or throws an error if the index is out of bounds.
*/
public A index(final int i) {
if (i < 0 || i >= length())
throw error("Index " + i + "out of bounds.");
return ftree.lookup(Function.<Integer>identity(), i)._2();
}
public <B> B foldLeft(final F2<B, A, B> f, final B z) {
return ftree.foldLeft(f, z);
}
public <B> B foldRight(final F2<A, B, B> f, final B z) {
return ftree.foldRight(f, z);
}
@Override
public int hashCode() {
return Hash.seqHash(Hash.<A>anyHash()).hash(this);
}
public <B> Seq<B> map(F<A, B> f) {
return new Seq<B>(ftree.map(f, Seq.<B>elemMeasured()));
}
}