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comparison src/main/java/fj/data/Seq.java @ 0:fe80c1edf1be

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add getLoop
author tatsuki
date Fri, 20 Mar 2015 21:04:03 +0900
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-1:000000000000 0:fe80c1edf1be
1 package fj.data;
2
3 import fj.F;
4 import fj.F2;
5 import fj.Function;
6 import static fj.Bottom.error;
7 import static fj.Monoid.intAdditionMonoid;
8 import static fj.data.fingertrees.FingerTree.measured;
9
10 import fj.data.fingertrees.FingerTree;
11 import fj.data.fingertrees.MakeTree;
12 import fj.data.fingertrees.Measured;
13
14 /**
15 * Provides an immutable finite sequence, implemented as a finger tree. This structure gives O(1) access to
16 * the head and tail, as well as O(log n) random access and concatenation of sequences.
17 */
18 public final class Seq<A> {
19 private static final Measured<Integer, Object> ELEM_MEASURED = measured(intAdditionMonoid, Function.constant(1));
20 private static final MakeTree<Integer, Object> MK_TREE = FingerTree.mkTree(ELEM_MEASURED);
21 private static final Seq<Object> EMPTY = new Seq<Object>(MK_TREE.empty());
22
23 @SuppressWarnings("unchecked")
24 private static <A> MakeTree<Integer, A> mkTree() {
25 return (MakeTree<Integer, A>) MK_TREE;
26 }
27
28 private final FingerTree<Integer, A> ftree;
29
30 private Seq(final FingerTree<Integer, A> ftree) {
31 this.ftree = ftree;
32 }
33
34 @SuppressWarnings("unchecked")
35 private static <A> Measured<Integer, A> elemMeasured() {
36 return (Measured<Integer, A>) ELEM_MEASURED;
37 }
38
39 /**
40 * The empty sequence.
41 *
42 * @return A sequence with no elements.
43 */
44 @SuppressWarnings("unchecked")
45 public static <A> Seq<A> empty() {
46 return (Seq<A>) EMPTY;
47 }
48
49 /**
50 * A singleton sequence.
51 *
52 * @param a The single element in the sequence.
53 * @return A new sequence with the given element in it.
54 */
55 public static <A> Seq<A> single(final A a) {
56 return new Seq<A>(Seq.<A>mkTree().single(a));
57 }
58
59 /**
60 * Inserts the given element at the front of this sequence.
61 *
62 * @param a An element to insert at the front of this sequence.
63 * @return A new sequence with the given element at the front.
64 */
65 public Seq<A> cons(final A a) {
66 return new Seq<A>(ftree.cons(a));
67 }
68
69 /**
70 * Inserts the given element at the end of this sequence.
71 *
72 * @param a An element to insert at the end of this sequence.
73 * @return A new sequence with the given element at the end.
74 */
75 public Seq<A> snoc(final A a) {
76 return new Seq<A>(ftree.snoc(a));
77 }
78
79 /**
80 * Appends the given sequence to this sequence.
81 *
82 * @param as A sequence to append to this one.
83 * @return A new sequence with the given sequence appended to this one.
84 */
85 public Seq<A> append(final Seq<A> as) {
86 return new Seq<A>(ftree.append(as.ftree));
87 }
88
89 /**
90 * Checks if this is the empty sequence.
91 *
92 * @return True if this sequence is empty, otherwise false.
93 */
94 public boolean isEmpty() {
95 return ftree.isEmpty();
96 }
97
98 /**
99 * Returns the number of elements in this sequence.
100 *
101 * @return the number of elements in this sequence.
102 */
103 public int length() {
104 return ftree.measure();
105 }
106
107 /**
108 * Returns the element at the given index.
109 *
110 * @param i The index of the element to return.
111 * @return The element at the given index, or throws an error if the index is out of bounds.
112 */
113 public A index(final int i) {
114 if (i < 0 || i >= length())
115 throw error("Index " + i + "out of bounds.");
116 return ftree.lookup(Function.<Integer>identity(), i)._2();
117 }
118
119 public <B> B foldLeft(final F2<B, A, B> f, final B z) {
120 return ftree.foldLeft(f, z);
121 }
122
123 public <B> B foldRight(final F2<A, B, B> f, final B z) {
124 return ftree.foldRight(f, z);
125 }
126
127 public <B> Seq<B> map(F<A, B> f) {
128 return new Seq<B>(ftree.map(f, Seq.<B>elemMeasured()));
129 }
130
131 }