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Seq.java
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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;
import java.util.AbstractList;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* 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> implements Iterable<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.equals0(Seq.class, this, other, () -> Equal.seqEqual(Equal.<A>anyEqual()));
}
/**
* 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));
}
/**
* The first element of this sequence. This is an O(1) operation.
*
* @return The first element if this sequence is nonempty, otherwise throws an error.
*/
public A head() { return ftree.head(); }
/**
* The last element of this sequence. This is an O(1) operation.
*
* @return The last element if this sequence is nonempty, otherwise throws an error.
*/
public A last() { return ftree.last(); }
/**
* The sequence without the first element. This is an O(1) operation.
*
* @return The sequence without the first element if this sequence is nonempty, otherwise throws an error.
*/
public Seq<A> tail() {
return (length() == 1) ? empty() : new Seq<>(ftree.tail());
}
/**
* The sequence without the last element. This is an O(1) operation.
*
* @return The sequence without the last element if this sequence is nonempty, otherwise throws an error.
*/
public Seq<A> init() {
return (length() == 1) ? empty() : new Seq<>(ftree.init());
}
public Stream<A> toStream() {
return ftree.foldLeft((b, a) -> b.cons(a), Stream.<A>nil()).reverse();
}
public final java.util.List<A> toJavaList() {
return new AbstractList<A>() {
@Override public A get(int i) { return index(i); }
@Override public Iterator<A> iterator() { return Seq.this.iterator(); }
@Override public int size() { return length(); }
};
}
/**
* Returns an iterator for this seq. This method exists to permit the use in a <code>for</code>-each loop.
*
* @return A iterator for this seq.
*/
public final Iterator<A> iterator() {
return new Iterator<A>() {
private FingerTree<Integer, A> ftree = Seq.this.ftree;
public boolean hasNext() {
return !ftree.isEmpty();
}
public A next() {
if (ftree.isEmpty())
throw new NoSuchElementException();
else {
final A a = ftree.head();
ftree = ftree.tail();
return a;
}
}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
@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();
}
public P2<Seq<A>, Seq<A>> split(final int i) {
final P2<FingerTree<Integer, A>, FingerTree<Integer, A>> lr = ftree.split(index -> index > i);
return P.p(new Seq<>(lr._1()), new Seq<>(lr._2()));
}
/**
* Returns the element at the given index. This is an O(log(n)) operation.
*
* @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) {
checkBounds(i);
return ftree.lookup(Function.<Integer>identity(), i)._2();
}
/**
* Replace the element at the given index with the supplied value. This is an O(log(n)) operation.
*
* @param i The index of the element to update.
* @param a The new value.
*
* @return The updated sequence, or throws an error if the index is out of bounds.
*/
public Seq<A> update(final int i, final A a) {
checkBounds(i);
final P3<FingerTree<Integer, A>, A, FingerTree<Integer, A>> lxr = ftree.split1(index -> index > i);
return new Seq<>(lxr._1().append(lxr._3().cons(a)));
}
/**
* Takes the given number of elements from the head of this sequence if they are available.
*
* @param n The maximum number of elements to take from this sequence.
* @return A sequence consisting only of the first n elements of this sequence, or else the whole sequence,
* if it has less than n elements.
*/
public Seq<A> take(final int n) { return split(n)._1(); }
/**
* Drops the given number of elements from the head of this sequence if they are available.
*
* @param n The number of elements to drop from this sequence.
* @return A sequence consisting of all elements of this sequence except the first n ones, or else the empty sequence,
* if this sequence has less than n elements.
*/
public Seq<A> drop(final int n) { return split(n)._2(); }
private void checkBounds(final int i) { if (i < 0 || i >= length()) throw error("Index " + i + " is out of bounds."); }
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()));
}
}