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Functional patterns for Java

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package com.jnape.palatable.lambda.semigroup.builtin;

import com.jnape.palatable.lambda.functions.Fn1;
import com.jnape.palatable.lambda.functions.specialized.SemigroupFactory;
import com.jnape.palatable.lambda.monoid.Monoid;
import com.jnape.palatable.lambda.semigroup.Semigroup;

import java.util.concurrent.CompletableFuture;

/**
 * A {@link Semigroup} instance formed by {@link CompletableFuture}<A> and a semigroup over
 * A. If either {@link CompletableFuture}s completes exceptionally, the result is also an exceptionally
 * completed future.
 * 
 * Note that this operation only takes as long as the slowest future to complete.
 * 
 * For the {@link Monoid}, see {@link com.jnape.palatable.lambda.monoid.builtin.Compose}.
 *
 * @param  the future parameter type
 */
public final class Compose implements SemigroupFactory, CompletableFuture> {

    private static final Compose INSTANCE = new Compose<>();

    private Compose() {
    }

    @Override
    public Semigroup> checkedApply(Semigroup aSemigroup) {
        return (futureX, futureY) -> futureX.thenCompose(x -> futureY.thenApply(y -> aSemigroup.apply(x, y)));
    }

    @SuppressWarnings("unchecked")
    public static  Compose compose() {
        return (Compose) INSTANCE;
    }

    public static  Semigroup> compose(Semigroup aSemigroup) {
        return Compose.compose().apply(aSemigroup);
    }

    public static  Fn1, CompletableFuture> compose(Semigroup aSemigroup,
                                                                              CompletableFuture x) {
        return compose(aSemigroup).apply(x);
    }

    public static  CompletableFuture compose(Semigroup aSemigroup,
                                                   CompletableFuture x,
                                                   CompletableFuture y) {
        return compose(aSemigroup, x).apply(y);
    }
}