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Max/Min/-By semigroups
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‎CHANGELOG.md

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@@ -8,6 +8,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/).
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- `Fn3-8` static factory overloads to aid in coercing lambdas
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- Adding composition guarantees to `LensLike`
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- `CmpEqBy`, `CmpEq`, `GTBy`, `GT`, `LTBy`, `LT`, `GTEBy`, `GTE`, `LTEBy`, and `LTE` inequality checks
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- `MinBy`, `MaxBy`, `Min`, and `Max` semigroups
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## [3.0.3] - 2018-05-27
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### Added

‎src/main/java/com/jnape/palatable/lambda/semigroup/builtin/Max.java

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package com.jnape.palatable.lambda.semigroup.builtin;
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import com.jnape.palatable.lambda.functions.Fn1;
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import com.jnape.palatable.lambda.semigroup.Semigroup;
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import static com.jnape.palatable.lambda.functions.builtin.fn1.Id.id;
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import static com.jnape.palatable.lambda.semigroup.builtin.MaxBy.maxBy;
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/**
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* A {@link Semigroup} over <code>A</code> that chooses between two values <code>x</code> and <code>y</code> via the
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* following rules:
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* <ul>
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* <li>If <code>x</code> is strictly less than <code>y</code>, return <code>y</code></li>
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* <li>Otherwise, return <code>x</code></li>
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* </ul>
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*
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* @param <A> the value type
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* @see MaxBy
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* @see Min
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*/
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public final class Max<A extends Comparable<A>> implements Semigroup<A> {
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private static final Max INSTANCE = new Max();
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private Max() {
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}
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@Override
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public A apply(A x, A y) {
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return maxBy(id(), x, y);
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}
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@SuppressWarnings("unchecked")
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public static <A extends Comparable<A>> Max<A> max() {
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return INSTANCE;
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}
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public static <A extends Comparable<A>> Fn1<A, A> max(A x) {
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return Max.<A>max().apply(x);
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}
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public static <A extends Comparable<A>> A max(A x, A y) {
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return max(x).apply(y);
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}
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}

‎src/main/java/com/jnape/palatable/lambda/semigroup/builtin/MaxBy.java

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package com.jnape.palatable.lambda.semigroup.builtin;
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import com.jnape.palatable.lambda.functions.Fn1;
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import com.jnape.palatable.lambda.functions.specialized.SemigroupFactory;
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import com.jnape.palatable.lambda.semigroup.Semigroup;
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import java.util.function.Function;
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import static com.jnape.palatable.lambda.functions.builtin.fn3.LTBy.ltBy;
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/**
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* Given a mapping function from some type <code>A</code> to some {@link Comparable} type <code>B</code>, produce a
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* {@link Semigroup} over <code>A</code> that chooses between two values <code>x</code> and <code>y</code> via the
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* following rules:
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* <ul>
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* <li>If <code>x</code> is strictly less than <code>y</code> in terms of <code>B</code>, return <code>y</code></li>
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* <li>Otherwise, return <code>x</code></li>
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* </ul>
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*
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* @param <A> the value type
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* @param <B> the mapped comparison type
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* @see Max
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* @see MinBy
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*/
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public final class MaxBy<A, B extends Comparable<B>> implements SemigroupFactory<Function<? super A, ? extends B>, A> {
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private static final MaxBy INSTANCE = new MaxBy();
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private MaxBy() {
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}
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@Override
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public Semigroup<A> apply(Function<? super A, ? extends B> compareFn) {
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return (x, y) -> ltBy(compareFn, x, y) ? y : x;
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}
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@SuppressWarnings("unchecked")
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public static <A, B extends Comparable<B>> MaxBy<A, B> maxBy() {
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return INSTANCE;
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}
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public static <A, B extends Comparable<B>> Semigroup<A> maxBy(
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Function<? super A, ? extends B> compareFn) {
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return MaxBy.<A, B>maxBy().apply(compareFn);
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}
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public static <A, B extends Comparable<B>> Fn1<A, A> maxBy(Function<? super A, ? extends B> compareFn, A x) {
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return MaxBy.<A, B>maxBy(compareFn).apply(x);
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}
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public static <A, B extends Comparable<B>> A maxBy(Function<? super A, ? extends B> compareFn, A x, A y) {
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return maxBy(compareFn, x).apply(y);
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}
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}

‎src/main/java/com/jnape/palatable/lambda/semigroup/builtin/Min.java

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package com.jnape.palatable.lambda.semigroup.builtin;
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import com.jnape.palatable.lambda.functions.Fn1;
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import com.jnape.palatable.lambda.semigroup.Semigroup;
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import static com.jnape.palatable.lambda.functions.builtin.fn1.Id.id;
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import static com.jnape.palatable.lambda.semigroup.builtin.MinBy.minBy;
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/**
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* A {@link Semigroup} over <code>A</code> that chooses between two values <code>x</code> and <code>y</code> via the
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* following rules:
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* <ul>
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* <li>If <code>x</code> is strictly greater than <code>y</code>, return <code>y</code></li>
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* <li>Otherwise, return <code>x</code></li>
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* </ul>
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*
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* @param <A> the value type
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* @see MinBy
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* @see Max
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*/
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public final class Min<A extends Comparable<A>> implements Semigroup<A> {
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private static final Min INSTANCE = new Min();
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private Min() {
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}
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@Override
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public A apply(A x, A y) {
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return minBy(id(), x, y);
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}
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@SuppressWarnings("unchecked")
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public static <A extends Comparable<A>> Min<A> min() {
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return INSTANCE;
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}
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public static <A extends Comparable<A>> Fn1<A, A> min(A x) {
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return Min.<A>min().apply(x);
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}
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public static <A extends Comparable<A>> A min(A x, A y) {
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return min(x).apply(y);
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}
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}

‎src/main/java/com/jnape/palatable/lambda/semigroup/builtin/MinBy.java

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package com.jnape.palatable.lambda.semigroup.builtin;
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import com.jnape.palatable.lambda.functions.Fn1;
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import com.jnape.palatable.lambda.functions.specialized.SemigroupFactory;
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import com.jnape.palatable.lambda.semigroup.Semigroup;
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import java.util.function.Function;
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import static com.jnape.palatable.lambda.functions.builtin.fn3.GTBy.gtBy;
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/**
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* Given a mapping function from some type <code>A</code> to some {@link Comparable} type <code>B</code>, produce a
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* {@link Semigroup} over <code>A</code> that chooses between two values <code>x</code> and <code>y</code> via the
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* following rules:
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* <ul>
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* <li>If <code>x</code> is strictly greater than <code>y</code> in terms of <code>B</code>, return <code>y</code></li>
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* <li>Otherwise, return <code>x</code></li>
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* </ul>
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*
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* @param <A> the value type
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* @param <B> the mapped comparison type
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* @see Min
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* @see MaxBy
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*/
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public final class MinBy<A, B extends Comparable<B>> implements SemigroupFactory<Function<? super A, ? extends B>, A> {
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private static final MinBy INSTANCE = new MinBy();
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private MinBy() {
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}
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@Override
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public Semigroup<A> apply(Function<? super A, ? extends B> compareFn) {
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return (x, y) -> gtBy(compareFn, x, y) ? y : x;
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}
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@SuppressWarnings("unchecked")
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public static <A, B extends Comparable<B>> MinBy<A, B> minBy() {
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return INSTANCE;
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}
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public static <A, B extends Comparable<B>> Semigroup<A> minBy(
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Function<? super A, ? extends B> compareFn) {
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return MinBy.<A, B>minBy().apply(compareFn);
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}
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public static <A, B extends Comparable<B>> Fn1<A, A> minBy(Function<? super A, ? extends B> compareFn, A x) {
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return MinBy.<A, B>minBy(compareFn).apply(x);
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}
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public static <A, B extends Comparable<B>> A minBy(Function<? super A, ? extends B> compareFn, A x, A y) {
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return minBy(compareFn, x).apply(y);
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}
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}

‎src/test/java/com/jnape/palatable/lambda/semigroup/builtin/MaxByTest.java

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package com.jnape.palatable.lambda.semigroup.builtin;
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import org.junit.Test;
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import static com.jnape.palatable.lambda.functions.builtin.fn1.Id.id;
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import static com.jnape.palatable.lambda.semigroup.builtin.MaxBy.maxBy;
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import static org.junit.Assert.assertEquals;
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public class MaxByTest {
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@Test
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public void semigroup() {
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assertEquals((Integer) 1, maxBy(id(), 1, 0));
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assertEquals((Integer) 1, maxBy(id(), 1, 1));
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assertEquals((Integer) 2, maxBy(id(), 1, 2));
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assertEquals("ab", maxBy(String::length, "ab", "a"));
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assertEquals("ab", maxBy(String::length, "ab", "cd"));
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assertEquals("bc", maxBy(String::length, "a", "bc"));
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}
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}

‎src/test/java/com/jnape/palatable/lambda/semigroup/builtin/MaxTest.java

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package com.jnape.palatable.lambda.semigroup.builtin;
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import org.junit.Test;
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import static com.jnape.palatable.lambda.semigroup.builtin.Max.max;
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import static org.junit.Assert.assertEquals;
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public class MaxTest {
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@Test
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public void semigroup() {
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assertEquals((Integer) 1, max(1, 0));
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assertEquals((Integer) 1, max(1, 1));
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assertEquals((Integer) 2, max(1, 2));
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}
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}

‎src/test/java/com/jnape/palatable/lambda/semigroup/builtin/MinByTest.java

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package com.jnape.palatable.lambda.semigroup.builtin;
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import org.junit.Test;
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import static com.jnape.palatable.lambda.functions.builtin.fn1.Id.id;
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import static com.jnape.palatable.lambda.semigroup.builtin.MinBy.minBy;
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import static org.junit.Assert.assertEquals;
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public class MinByTest {
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@Test
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public void semigroup() {
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assertEquals((Integer) 1, minBy(id(), 1, 2));
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assertEquals((Integer) 1, minBy(id(), 1, 1));
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assertEquals((Integer) 0, minBy(id(), 1, 0));
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assertEquals("a", minBy(String::length, "a", "ab"));
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assertEquals("ab", minBy(String::length, "ab", "cd"));
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assertEquals("c", minBy(String::length, "ab", "c"));
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}
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}

‎src/test/java/com/jnape/palatable/lambda/semigroup/builtin/MinTest.java

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package com.jnape.palatable.lambda.semigroup.builtin;
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import org.junit.Test;
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import static com.jnape.palatable.lambda.semigroup.builtin.Min.min;
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import static org.junit.Assert.assertEquals;
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public class MinTest {
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@Test
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public void semigroup() {
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assertEquals((Integer) 1, min(1, 2));
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assertEquals((Integer) 1, min(1, 1));
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assertEquals((Integer) 0, min(1, 0));
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}
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}

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