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Functional patterns for Java

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

import com.jnape.palatable.lambda.functions.Fn1;
import com.jnape.palatable.lambda.iterators.ConcatenatingIterator;
import com.jnape.palatable.lambda.monoid.Monoid;

import java.util.Collections;

/**
 * The {@link Monoid} instance formed under concatenation for an arbitrary {@link Iterable}.
 *
 * @see Monoid
 */
public final class Concat implements Monoid> {

    private static final Concat INSTANCE = new Concat();

    private Concat() {
    }

    @Override
    public Iterable identity() {
        return Collections::emptyIterator;
    }

    @Override
    public Iterable apply(Iterable xs, Iterable ys) {
        return () -> new ConcatenatingIterator<>(xs, ys);
    }

    @SuppressWarnings("unchecked")
    public static  Concat concat() {
        return INSTANCE;
    }

    public static  Fn1, Iterable> concat(Iterable xs) {
        return Concat.concat().apply(xs);
    }

    public static  Iterable concat(Iterable xs, Iterable ys) {
        return concat(xs).apply(ys);
    }
}