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LiftA2 receives more parameters to aid inference
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‎CHANGELOG.md‎

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@@ -25,6 +25,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/).
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- `Into3-8` now accept a product of the same cardinality, instead of requiring a tuple
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- `CoProduct2-8#project` now return generalized products
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- `Choice2-8#project` return tuples
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- `liftA2` receives more parameters to aid inference
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## [3.0.3] - 2018-05-27
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### Added

‎src/main/java/com/jnape/palatable/lambda/functions/builtin/fn3/LiftA2.java‎

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@@ -7,50 +7,54 @@
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import java.util.function.BiFunction;
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import static com.jnape.palatable.lambda.functions.Fn2.fn2;
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/**
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* Lift into and apply a {@link BiFunction} to two {@link Applicative} values, returning the result inside the same
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* {@link Applicative} context. Equivalent ot <code>appB.zip(appA.fmap(fn))</code>.
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* {@link Applicative} context. Functionally equivalent to <code>appB.zip(appA.fmap(fn))</code>.
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*
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* @param <A> the function's first argument type
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* @param <B> the function's second argument type
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* @param <C> the function's return type
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* @param <App> the applicative unification type
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* @param <A> the function's first argument type
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* @param <B> the function's second argument typ
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* @param <C> the function's return type
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* @param <App> the applicative unification type
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* @param <AppA> the inferred first applicative argument type
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* @param <AppB> the inferred second applicative argument type
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* @param <AppC> the inferred applicative return type
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* @see Applicative#zip(Applicative)
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*/
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public final class LiftA2<A, B, C, App extends Applicative> implements Fn3<BiFunction<? super A, ? super B, ? extends C>,
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Applicative<A, App>, Applicative<B, App>, Applicative<C, App>> {
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public final class LiftA2<A, B, C, App extends Applicative,
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AppA extends Applicative<A, App>,
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AppB extends Applicative<B, App>,
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AppC extends Applicative<C, App>> implements Fn3<BiFunction<? super A, ? super B, ? extends C>, AppA, AppB, AppC> {
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private static final LiftA2 INSTANCE = new LiftA2();
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private LiftA2() {
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}
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@Override
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public Applicative<C, App> apply(BiFunction<? super A, ? super B, ? extends C> fn,
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Applicative<A, App> appA,
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Applicative<B, App> appB) {
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return appB.zip(appA.fmap(fn2(fn)));
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public AppC apply(BiFunction<? super A, ? super B, ? extends C> fn, AppA appA, AppB appB) {
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return appB.zip(appA.fmap(Fn2.<A, B, C>fn2(fn))).coerce();
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}
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@SuppressWarnings("unchecked")
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public static <A, B, C, App extends Applicative> LiftA2<A, B, C, App> liftA2() {
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public static <A, B, C, App extends Applicative, AppA extends Applicative<A, App>, AppB extends Applicative<B, App>, AppC extends Applicative<C, App>> LiftA2<A, B, C, App, AppA, AppB, AppC> liftA2() {
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return INSTANCE;
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}
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public static <A, B, C, App extends Applicative> Fn2<Applicative<A, App>, Applicative<B, App>, Applicative<C, App>> liftA2(
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public static <A, B, C, App extends Applicative, AppA extends Applicative<A, App>, AppB extends Applicative<B, App>, AppC extends Applicative<C, App>> Fn2<AppA, AppB, AppC> liftA2(
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BiFunction<? super A, ? super B, ? extends C> fn) {
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return LiftA2.<A, B, C, App>liftA2().apply(fn);
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return LiftA2.<A, B, C, App, AppA, AppB, AppC>liftA2().apply(fn);
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}
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public static <A, B, C, App extends Applicative> Fn1<Applicative<B, App>, Applicative<C, App>> liftA2(
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BiFunction<? super A, ? super B, ? extends C> fn, Applicative<A, App> appA) {
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return LiftA2.<A, B, C, App>liftA2(fn).apply(appA);
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public static <A, B, C, App extends Applicative, AppA extends Applicative<A, App>, AppB extends Applicative<B, App>, AppC extends Applicative<C, App>> Fn1<AppB, AppC> liftA2(
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BiFunction<? super A, ? super B, ? extends C> fn,
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AppA appA) {
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return LiftA2.<A, B, C, App, AppA, AppB, AppC>liftA2(fn).apply(appA);
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}
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public static <A, B, C, App extends Applicative> Applicative<C, App> liftA2(
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BiFunction<? super A, ? super B, ? extends C> fn, Applicative<A, App> appA, Applicative<B, App> appB) {
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return LiftA2.<A, B, C, App>liftA2(fn, appA).apply(appB);
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public static <A, B, C, App extends Applicative, AppA extends Applicative<A, App>, AppB extends Applicative<B, App>, AppC extends Applicative<C, App>> AppC liftA2(
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BiFunction<? super A, ? super B, ? extends C> fn,
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AppA appA,
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AppB appB) {
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return LiftA2.<A, B, C, App, AppA, AppB, AppC>liftA2(fn, appA).apply(appB);
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}
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}

‎src/test/java/com/jnape/palatable/lambda/functions/builtin/fn3/LiftA2Test.java‎

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package com.jnape.palatable.lambda.functions.builtin.fn3;
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import com.jnape.palatable.lambda.functor.builtin.Identity;
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import com.jnape.palatable.lambda.adt.Either;
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import com.jnape.palatable.lambda.adt.Maybe;
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import org.junit.Test;
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import java.util.function.BiFunction;
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import static com.jnape.palatable.lambda.adt.Either.left;
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import static com.jnape.palatable.lambda.adt.Either.right;
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import static com.jnape.palatable.lambda.adt.hlist.HList.tuple;
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import static com.jnape.palatable.lambda.adt.Maybe.just;
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import static com.jnape.palatable.lambda.adt.Maybe.nothing;
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import static com.jnape.palatable.lambda.functions.builtin.fn3.LiftA2.liftA2;
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import static org.junit.Assert.assertEquals;
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public class LiftA2Test {
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@Test
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public void liftsAndAppliesDyadicFunctionToTwoApplicatives() {
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public void inference() {
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BiFunction<Integer, Integer, Integer> add = (x, y) -> x + y;
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assertEquals(right(3), liftA2(add, right(1), right(2)).coerce());
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assertEquals(tuple(1, 5), liftA2(add, tuple(1, 2), tuple(2, 3)).coerce());
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assertEquals(new Identity<>(3), liftA2(add, new Identity<>(1), new Identity<>(2)));
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Maybe<Integer> a = liftA2(add, just(1), just(2));
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assertEquals(just(3), a);
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Maybe<Integer> b = liftA2(add, just(1), nothing());
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assertEquals(nothing(), b);
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Maybe<Integer> c = liftA2(add, nothing(), just(2));
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assertEquals(nothing(), c);
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Maybe<Integer> d = liftA2(add, nothing(), nothing());
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assertEquals(nothing(), d);
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Either<String, Integer> e = liftA2(add, Either.<String, Integer>right(1), right(2));
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assertEquals(right(3), e);
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Either<String, Integer> f = liftA2(add, left("error"), right(2));
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assertEquals(left("error"), f);
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Either<String, Integer> g = liftA2(add, right(1), left("error"));
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assertEquals(left("error"), g);
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Either<String, Integer> h = liftA2(add, left("error"), left("another error"));
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assertEquals(left("error"), h);
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}
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}

‎src/test/java/com/jnape/palatable/lambda/traversable/TraversableTest.java‎

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public class TraversableTest {
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@Test
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public void compilation() {
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public void inference() {
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Either<String, Maybe<Integer>> a = just(Either.<String, Integer>right(1)).traverse(id(), Either::right);
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assertEquals(right(just(1)), a);
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