Mercurial > hg > Members > tatsuki > functionaljava-master > core
view src/main/java/fj/data/Enumerator.java @ 0:fe80c1edf1be
add getLoop
author | tatsuki |
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date | Fri, 20 Mar 2015 21:04:03 +0900 |
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package fj.data; import fj.F; import fj.F2; import static fj.Function.*; import static fj.data.Option.none; import static fj.data.Option.some; import fj.Function; import fj.Ord; import static fj.Ord.*; import fj.Ordering; import static fj.Ordering.*; import java.math.BigDecimal; import java.math.BigInteger; /** * Abstracts over a type that may have a successor and/or predecessor value. This implies ordering for that type. A user * may construct an enumerator with an optimised version for <code>plus</code>, otherwise a default is implemented using * the given successor/predecessor implementations. * <p/> * For any enumerator e, the following laws must satisfy: * <ul> * <li>forall a. e.successor(a).forall(\t -> e.predecessor(t).forall(\z -> z == a))</li> * <li>forall a. e.predecessor(a).forall(\t -> e.successor(t).forall(\z -> z == a))</li> * <li>e.max().forall(\t -> e.successor(t).isNone)</li> * <li>e.min().forall(\t -> e.predecessor(t).isNone)</li> * <li>forall a n. e.plus(a, 0) == Some(a)</li> * <li>forall a n | n > 0. e.plus(a, n) == e.plus(a, n - 1)</li> * <li>forall a n | n < 0. e.plus(a, n) == e.plus(a, n + 1)</li> * </ul> * * @version %build.number% */ public final class Enumerator<A> { private final F<A, Option<A>> successor; private final F<A, Option<A>> predecessor; private final Option<A> max; private final Option<A> min; private final Ord<A> order; private final F<A, F<Long, Option<A>>> plus; private Enumerator(final F<A, Option<A>> successor, final F<A, Option<A>> predecessor, final Option<A> max, final Option<A> min, final Ord<A> order, final F<A, F<Long, Option<A>>> plus) { this.successor = successor; this.predecessor = predecessor; this.max = max; this.min = min; this.order = order; this.plus = plus; } /** * Returns the potential successor of a value for this enumerator in curried form. * * @return The potential successor of a value for this enumerator in curried form. */ public F<A, Option<A>> successor() { return successor; } /** * Returns the potential successor of a value for this enumerator. * * @param a The value to return the successor of. * @return The potential successor of a value for this enumerator. */ public Option<A> successor(final A a) { return successor.f(a); } /** * Returns the potential predecessor of a value for this enumerator in curried form. * * @return The potential predecessor of a value for this enumerator in curried form. */ public F<A, Option<A>> predecessor() { return predecessor; } /** * Returns the potential predecessor of a value for this enumerator. * * @param a The value to return the predecessor of. * @return The potential predecessor of a value for this enumerator. */ public Option<A> predecessor(final A a) { return predecessor.f(a); } /** * Returns the maximum value for this enumerator if there is one. * * @return The maximum value for this enumerator if there is one. */ public Option<A> max() { return max; } /** * Returns the minimum value for this enumerator if there is one. * * @return The minimum value for this enumerator if there is one. */ public Option<A> min() { return min; } /** * Returns a function that moves a value along the enumerator a given number of times. * * @return A function that moves a value along the enumerator a given number of times. */ public F<A, F<Long, Option<A>>> plus() { return plus; } /** * Returns a function that moves a value along the enumerator a given number of times. * * @param a The value to begin moving along from. * @return A function that moves a value along the enumerator a given number of times. */ public F<Long, Option<A>> plus(final A a) { return plus.f(a); } /** * Returns a function that moves a value along the enumerator a given number of times. * * @param l The number of times to move along the enumerator. * @return A function that moves a value along the enumerator a given number of times. */ public F<A, Option<A>> plus(final long l) { return flip(plus).f(l); } /** * Moves a value along the enumerator a given number of times. * * @param a The value to begin moving along from. * @param l The number of times to move along the enumerator. * @return A potential value after having moved the given number of times. */ public Option<A> plus(final A a, final long l) { return plus.f(a).f(l); } /** * Returns the ordering for the enumerator. * * @return The ordering for the enumerator. */ public Ord<A> order() { return order; } /** * Invariant functor map over this enumerator. * * @param f The covariant map. * @param g The contra-variant map. * @return An enumerator after the given functions are applied. */ public <B> Enumerator<B> xmap(final F<A, B> f, final F<B, A> g) { final F<Option<A>, Option<B>> of = new F<Option<A>, Option<B>>() { public Option<B> f(final Option<A> o) { return o.map(f); } }; return enumerator(compose(compose(of, successor), g), compose(compose(of, predecessor), g), max.map(f), min.map(f), order.comap(g), compose(compose(Function.<Long, Option<A>, Option<B>>compose().f(of), plus), g)); } /** * Returns a stream of the values from this enumerator, starting at the given value, counting up. * * @param a A value at which to begin the stream. * @return a stream of the values from this enumerator, starting at the given value, counting up. */ public Stream<A> toStream(final A a) { final F<A, A> id = identity(); return Stream.fromFunction(this, id, a); } /** * Create a new enumerator with the given minimum value. * * @param min A minimum value. * @return A new enumerator identical to this one, but with the given minimum value. */ public Enumerator<A> setMin(final Option<A> min) { return enumerator(successor, predecessor, max, min, order, plus); } /** * Create a new enumerator with the given maximum value. * * @param max A maximum value. * @return A new enumerator identical to this one, but with the given maximum value. */ public Enumerator<A> setMax(final Option<A> max) { return enumerator(successor, predecessor, max, min, order, plus); } /** * Construct an enumerator. ` * * @param successor The successor function. * @param predecessor The predecessor function. * @param max The potential maximum value. * @param min The potential minimum value. * @param order The ordering for the type. * @param plus The function to move the enumeration a given number of times. This may be supplied for a performance * enhancement for certain types. * @return An enumerator with the given values. */ public static <A> Enumerator<A> enumerator(final F<A, Option<A>> successor, final F<A, Option<A>> predecessor, final Option<A> max, final Option<A> min, final Ord<A> order, final F<A, F<Long, Option<A>>> plus) { return new Enumerator<A>(successor, predecessor, max, min, order, plus); } /** * Construct an enumerator. The <code>plus</code> function is derived from the <code>successor</code> and * <code>predecessor</code>. * * @param successor The successor function. * @param predecessor The predecessor function. * @param max The potential maximum value. * @param min The potential minimum value. * @param order The ordering for the type. * @return An enumerator with the given values. */ public static <A> Enumerator<A> enumerator(final F<A, Option<A>> successor, final F<A, Option<A>> predecessor, final Option<A> max, final Option<A> min, final Ord<A> order) { return new Enumerator<A>(successor, predecessor, max, min, order, curry(new F2<A, Long, Option<A>>() { public Option<A> f(final A a, final Long l) { if (l == 0L) return some(a); else if (l < 0L) { A aa = a; for (long x = l; x < 0; x++) { final Option<A> s = predecessor.f(aa); if (s.isNone()) return none(); else aa = s.some(); } return some(aa); } else { A aa = a; for (long x = l; x > 0; x--) { final Option<A> s = successor.f(aa); if (s.isNone()) return none(); else aa = s.some(); } return some(aa); } } })); } /** * An enumerator for <code>boolean</code>. */ public static final Enumerator<Boolean> booleanEnumerator = enumerator(new F<Boolean, Option<Boolean>>() { public Option<Boolean> f(final Boolean b) { return b ? Option.<Boolean>none() : some(true); } }, new F<Boolean, Option<Boolean>>() { public Option<Boolean> f(final Boolean b) { return b ? some(false) : Option.<Boolean>none(); } }, some(true), some(false), booleanOrd); /** * An enumerator for <code>byte</code>. */ public static final Enumerator<Byte> byteEnumerator = enumerator(new F<Byte, Option<Byte>>() { public Option<Byte> f(final Byte b) { return b == Byte.MAX_VALUE ? Option.<Byte>none() : some((byte) (b + 1)); } }, new F<Byte, Option<Byte>>() { public Option<Byte> f(final Byte b) { return b == Byte.MIN_VALUE ? Option.<Byte>none() : some((byte) (b - 1)); } }, some(Byte.MAX_VALUE), some(Byte.MIN_VALUE), byteOrd); /** * An enumerator for <code>char</code>. */ public static final Enumerator<Character> charEnumerator = enumerator(new F<Character, Option<Character>>() { public Option<Character> f(final Character c) { return c == Character.MAX_VALUE ? Option.<Character>none() : some((char) (c + 1)); } }, new F<Character, Option<Character>>() { public Option<Character> f(final Character c) { return c == Character.MIN_VALUE ? Option.<Character>none() : some((char) (c - 1)); } }, some(Character.MAX_VALUE), some(Character.MIN_VALUE), charOrd); /** * An enumerator for <code>double</code>. */ public static final Enumerator<Double> doubleEnumerator = enumerator(new F<Double, Option<Double>>() { public Option<Double> f(final Double d) { return d == Double.MAX_VALUE ? Option.<Double>none() : some(d + 1D); } }, new F<Double, Option<Double>>() { public Option<Double> f(final Double d) { return d == Double.MIN_VALUE ? Option.<Double>none() : some(d - 1D); } }, some(Double.MAX_VALUE), some(Double.MIN_VALUE), doubleOrd); /** * An enumerator for <code>float</code>. */ public static final Enumerator<Float> floatEnumerator = enumerator(new F<Float, Option<Float>>() { public Option<Float> f(final Float f) { return f == Float.MAX_VALUE ? Option.<Float>none() : some(f + 1F); } }, new F<Float, Option<Float>>() { public Option<Float> f(final Float f) { return f == Float.MIN_VALUE ? Option.<Float>none() : some(f - 1F); } }, some(Float.MAX_VALUE), some(Float.MIN_VALUE), floatOrd); /** * An enumerator for <code>int</code>. */ public static final Enumerator<Integer> intEnumerator = enumerator(new F<Integer, Option<Integer>>() { public Option<Integer> f(final Integer i) { return i == Integer.MAX_VALUE ? Option.<Integer>none() : some(i + 1); } }, new F<Integer, Option<Integer>>() { public Option<Integer> f(final Integer i) { return i == Integer.MIN_VALUE ? Option.<Integer>none() : some(i - 1); } }, some(Integer.MAX_VALUE), some(Integer.MIN_VALUE), intOrd); /** * An enumerator for <code>BigInteger</code>. */ public static final Enumerator<BigInteger> bigintEnumerator = enumerator(new F<BigInteger, Option<BigInteger>>() { public Option<BigInteger> f(final BigInteger i) { return some(i.add(BigInteger.ONE)); } }, new F<BigInteger, Option<BigInteger>>() { public Option<BigInteger> f(final BigInteger i) { return some(i.subtract(BigInteger.ONE)); } }, Option.<BigInteger>none(), Option.<BigInteger>none(), bigintOrd, curry( new F2<BigInteger, Long, Option<BigInteger>>() { public Option<BigInteger> f(final BigInteger i, final Long l) { return some(i.add(BigInteger.valueOf(l))); } })); /** * An enumerator for <code>BigDecimal</code>. */ public static final Enumerator<BigDecimal> bigdecimalEnumerator = enumerator(new F<BigDecimal, Option<BigDecimal>>() { public Option<BigDecimal> f(final BigDecimal i) { return some(i.add(BigDecimal.ONE)); } }, new F<BigDecimal, Option<BigDecimal>>() { public Option<BigDecimal> f(final BigDecimal i) { return some(i.subtract(BigDecimal.ONE)); } }, Option.<BigDecimal>none(), Option.<BigDecimal>none(), bigdecimalOrd, curry( new F2<BigDecimal, Long, Option<BigDecimal>>() { public Option<BigDecimal> f(final BigDecimal d, final Long l) { return some(d.add(BigDecimal.valueOf(l))); } })); /** * An enumerator for <code>long</code>. */ public static final Enumerator<Long> longEnumerator = enumerator(new F<Long, Option<Long>>() { public Option<Long> f(final Long i) { return i == Long.MAX_VALUE ? Option.<Long>none() : some(i + 1L); } }, new F<Long, Option<Long>>() { public Option<Long> f(final Long i) { return i == Long.MIN_VALUE ? Option.<Long>none() : some(i - 1L); } }, some(Long.MAX_VALUE), some(Long.MIN_VALUE), longOrd); /** * An enumerator for <code>short</code>. */ public static final Enumerator<Short> shortEnumerator = enumerator(new F<Short, Option<Short>>() { public Option<Short> f(final Short i) { return i == Short.MAX_VALUE ? Option.<Short>none() : some((short) (i + 1)); } }, new F<Short, Option<Short>>() { public Option<Short> f(final Short i) { return i == Short.MIN_VALUE ? Option.<Short>none() : some((short) (i - 1)); } }, some(Short.MAX_VALUE), some(Short.MIN_VALUE), shortOrd); /** * An enumerator for <code>Ordering</code>. */ public static final Enumerator<Ordering> orderingEnumerator = enumerator(new F<Ordering, Option<Ordering>>() { public Option<Ordering> f(final Ordering o) { return o == LT ? some(EQ) : o == EQ ? some(GT) : Option.<Ordering>none(); } }, new F<Ordering, Option<Ordering>>() { public Option<Ordering> f(final Ordering o) { return o == GT ? some(EQ) : o == EQ ? some(LT) : Option.<Ordering>none(); } }, some(GT), some(LT), orderingOrd); /** * An enumerator for <code>Natural</code> */ public static final Enumerator<Natural> naturalEnumerator = enumerator(new F<Natural, Option<Natural>>() { public Option<Natural> f(final Natural n) { return Option.some(n.succ()); } }, new F<Natural, Option<Natural>>() { public Option<Natural> f(final Natural n) { return n.pred(); } }, Option.<Natural>none(), some(Natural.ZERO), naturalOrd, curry(new F2<Natural, Long, Option<Natural>>() { public Option<Natural> f(final Natural n, final Long l) { return some(n).apply(Natural.natural(l).map(Function.curry(new F2<Natural, Natural, Natural>() { public Natural f(final Natural n1, final Natural n2) { return n1.add(n2); } }))); } })); }