Mercurial > hg > Members > tatsuki > functionaljava-master > core
view src/main/java/fj/Monoid.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; import static fj.Function.curry; import static fj.Function.compose; import static fj.Function.flip; import fj.data.Array; import fj.data.List; import fj.data.Natural; import fj.data.Option; import fj.data.Set; import fj.data.Stream; import static fj.data.Stream.iterableStream; import java.math.BigInteger; import java.math.BigDecimal; /** * A monoid abstraction to be defined across types of the given type argument. Implementations must * follow the monoidal laws: * <ul> * <li><em>Left Identity</em>; forall x. sum(zero(), x) == x</li> * <li><em>Right Identity</em>; forall x. sum(x, zero()) == x</li> * <li><em>Associativity</em>; forall x. forall y. forall z. sum(sum(x, y), z) == sum(x, sum(y, z))</li> * </ul> * * @version %build.number% */ public final class Monoid<A> { private final F<A, F<A, A>> sum; private final A zero; private Monoid(final F<A, F<A, A>> sum, final A zero) { this.sum = sum; this.zero = zero; } /** * Returns a semigroup projection of this monoid. * * @return A semigroup projection of this monoid. */ public Semigroup<A> semigroup() { return Semigroup.semigroup(sum); } /** * Sums the two given arguments. * * @param a1 A value to sum with another. * @param a2 A value to sum with another. * @return The of the two given arguments. */ public A sum(final A a1, final A a2) { return sum.f(a1).f(a2); } /** * Returns a function that sums the given value according to this monoid. * * @param a1 The value to sum. * @return A function that sums the given value according to this monoid. */ public F<A, A> sum(final A a1) { return sum.f(a1); } /** * Returns a function that sums according to this monoid. * * @return A function that sums according to this monoid. */ public F<A, F<A, A>> sum() { return sum; } /** * The zero value for this monoid. * * @return The zero value for this monoid. */ public A zero() { return zero; } /** * Sums the given values with right-fold. * * @param as The values to sum. * @return The sum of the given values. */ public A sumRight(final List<A> as) { return as.foldRight(sum, zero); } /** * Sums the given values with right-fold. * * @param as The values to sum. * @return The sum of the given values. */ public A sumRight(final Stream<A> as) { return as.foldRight(new F2<A, P1<A>, A>() { public A f(final A a, final P1<A> ap1) { return sum(a, ap1._1()); } }, zero); } /** * Sums the given values with left-fold. * * @param as The values to sum. * @return The sum of the given values. */ public A sumLeft(final List<A> as) { return as.foldLeft(sum, zero); } /** * Sums the given values with left-fold. * * @param as The values to sum. * @return The sum of the given values. */ public A sumLeft(final Stream<A> as) { return as.foldLeft(sum, zero); } /** * Returns a function that sums the given values with left-fold. * * @return a function that sums the given values with left-fold. */ public F<List<A>, A> sumLeft() { return new F<List<A>, A>() { public A f(final List<A> as) { return sumLeft(as); } }; } /** * Returns a function that sums the given values with right-fold. * * @return a function that sums the given values with right-fold. */ public F<List<A>, A> sumRight() { return new F<List<A>, A>() { public A f(final List<A> as) { return sumRight(as); } }; } /** * Returns a function that sums the given values with left-fold. * * @return a function that sums the given values with left-fold. */ public F<Stream<A>, A> sumLeftS() { return new F<Stream<A>, A>() { public A f(final Stream<A> as) { return sumLeft(as); } }; } /** * Intersperses the given value between each two elements of the iterable, and sums the result. * * @param as An iterable of values to sum. * @param a The value to intersperse between values of the given iterable. * @return The sum of the given values and the interspersed value. */ public A join(final Iterable<A> as, final A a) { final Stream<A> s = iterableStream(as); return s.isEmpty() ? zero : s.foldLeft1(compose(sum, flip(sum).f(a))); } /** * Constructs a monoid from the given sum function and zero value, which must follow the monoidal * laws. * * @param sum The sum function for the monoid. * @param zero The zero for the monoid. * @return A monoid instance that uses the given sun function and zero value. */ public static <A> Monoid<A> monoid(final F<A, F<A, A>> sum, final A zero) { return new Monoid<A>(sum, zero); } /** * Constructs a monoid from the given sum function and zero value, which must follow the monoidal * laws. * * @param sum The sum function for the monoid. * @param zero The zero for the monoid. * @return A monoid instance that uses the given sun function and zero value. */ public static <A> Monoid<A> monoid(final F2<A, A, A> sum, final A zero) { return new Monoid<A>(curry(sum), zero); } /** * Constructs a monoid from the given semigroup and zero value, which must follow the monoidal laws. * * @param s The semigroup for the monoid. * @param zero The zero for the monoid. * @return A monoid instance that uses the given sun function and zero value. */ public static <A> Monoid<A> monoid(final Semigroup<A> s, final A zero) { return new Monoid<A>(s.sum(), zero); } /** * A monoid that adds integers. */ public static final Monoid<Integer> intAdditionMonoid = monoid(Semigroup.intAdditionSemigroup, 0); /** * A monoid that multiplies integers. */ public static final Monoid<Integer> intMultiplicationMonoid = monoid(Semigroup.intMultiplicationSemigroup, 1); /** * A monoid that adds doubles. */ public static final Monoid<Double> doubleAdditionMonoid = monoid(Semigroup.doubleAdditionSemigroup, 0.0); /** * A monoid that multiplies doubles. */ public static final Monoid<Double> doubleMultiplicationMonoid = monoid(Semigroup.doubleMultiplicationSemigroup, 1.0); /** * A monoid that adds big integers. */ public static final Monoid<BigInteger> bigintAdditionMonoid = monoid(Semigroup.bigintAdditionSemigroup, BigInteger.ZERO); /** * A monoid that multiplies big integers. */ public static final Monoid<BigInteger> bigintMultiplicationMonoid = monoid(Semigroup.bigintMultiplicationSemigroup, BigInteger.ONE); /** * A monoid that adds big decimals. */ public static final Monoid<BigDecimal> bigdecimalAdditionMonoid = monoid(Semigroup.bigdecimalAdditionSemigroup, BigDecimal.ZERO); /** * A monoid that multiplies big decimals. */ public static final Monoid<BigDecimal> bigdecimalMultiplicationMonoid = monoid(Semigroup.bigdecimalMultiplicationSemigroup, BigDecimal.ONE); /** * A monoid that adds natural numbers. */ public static final Monoid<Natural> naturalAdditionMonoid = monoid(Semigroup.naturalAdditionSemigroup, Natural.ZERO); /** * A monoid that multiplies natural numbers. */ public static final Monoid<Natural> naturalMultiplicationMonoid = monoid(Semigroup.naturalMultiplicationSemigroup, Natural.ONE); /** * A monoid that adds longs. */ public static final Monoid<Long> longAdditionMonoid = monoid(Semigroup.longAdditionSemigroup, 0L); /** * A monoid that multiplies longs. */ public static final Monoid<Long> longMultiplicationMonoid = monoid(Semigroup.longMultiplicationSemigroup, 1L); /** * A monoid that ORs booleans. */ public static final Monoid<Boolean> disjunctionMonoid = monoid(Semigroup.disjunctionSemigroup, false); /** * A monoid that XORs booleans. */ public static final Monoid<Boolean> exclusiveDisjunctionMonoid = monoid(Semigroup.exclusiveDisjunctionSemiGroup, false); /** * A monoid that ANDs booleans. */ public static final Monoid<Boolean> conjunctionMonoid = monoid(Semigroup.conjunctionSemigroup, true); /** * A monoid that appends strings. */ public static final Monoid<String> stringMonoid = monoid(Semigroup.stringSemigroup, ""); /** * A monoid that appends string buffers. */ public static final Monoid<StringBuffer> stringBufferMonoid = monoid(Semigroup.stringBufferSemigroup, new StringBuffer()); /** * A monoid that appends string builders. */ public static final Monoid<StringBuilder> stringBuilderMonoid = monoid(Semigroup.stringBuilderSemigroup, new StringBuilder()); /** * A monoid for functions. * * @param mb The monoid for the function codomain. * @return A monoid for functions. */ public static <A, B> Monoid<F<A, B>> functionMonoid(final Monoid<B> mb) { return monoid(Semigroup.<A, B>functionSemigroup(mb.semigroup()), Function.<A, B>constant(mb.zero)); } /** * A monoid for lists. * * @return A monoid for lists. */ public static <A> Monoid<List<A>> listMonoid() { return monoid(Semigroup.<A>listSemigroup(), List.<A>nil()); } /** * A monoid for options. * * @return A monoid for options. */ public static <A> Monoid<Option<A>> optionMonoid() { return monoid(Semigroup.<A>optionSemigroup(), Option.<A>none()); } /** * A monoid for options that take the first available value. * * @return A monoid for options that take the first available value. */ public static <A> Monoid<Option<A>> firstOptionMonoid() { return monoid(Semigroup.<A>firstOptionSemigroup(), Option.<A>none()); } /** * A monoid for options that take the last available value. * * @return A monoid for options that take the last available value. */ public static <A> Monoid<Option<A>> lastOptionMonoid() { return monoid(Semigroup.<A>lastOptionSemigroup(), Option.<A>none()); } /** * A monoid for streams. * * @return A monoid for streams. */ public static <A> Monoid<Stream<A>> streamMonoid() { return monoid(Semigroup.<A>streamSemigroup(), Stream.<A>nil()); } /** * A monoid for arrays. * * @return A monoid for arrays. */ @SuppressWarnings({"unchecked"}) public static <A> Monoid<Array<A>> arrayMonoid() { return monoid(Semigroup.<A>arraySemigroup(), Array.<A>empty()); } /** * A monoid for sets. * * @param o An order for set elements. * @return A monoid for sets whose elements have the given order. */ public static <A> Monoid<Set<A>> setMonoid(final Ord<A> o) { return monoid(Semigroup.<A>setSemigroup(), Set.empty(o)); } }