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Functional patterns for Java

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

import com.jnape.palatable.lambda.adt.Either;
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 static com.jnape.palatable.lambda.adt.Either.right;
import static com.jnape.palatable.lambda.functions.builtin.fn1.Constantly.constantly;

/**
 * A {@link Semigroup} instance formed by {@link Either}<L,R> and a semigroup over R.
 * The application to two {@link Either} values is right-biased, such that for a given {@link Either} x and
 * y:
 * 
 *  if both x and y are right values, the result is the application of the x and y values
 * in terms of the provided semigroup, wrapped in {@link Either#right}
 *  if only x is a right value, the result is x
 *  if only y is a right value, the result is y
 *  if neither x nor y are right values, the result is y
 * 
 * 
 * For the {@link Monoid}, see {@link com.jnape.palatable.lambda.monoid.builtin.RightAny}.
 *
 * @param  The left parameter type
 * @param  The right parameter type
 * @see Semigroup
 * @see Either
 */
public final class RightAny implements SemigroupFactory, Either> {

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

    private RightAny() {
    }

    @Override
    public Semigroup> checkedApply(Semigroup rSemigroup) {
        return (x, y) -> x.match(constantly(y),
                                 xR -> y.match(constantly(right(xR)),
                                               rSemigroup.apply(xR).fmap(Either::right)));
    }

    @SuppressWarnings("unchecked")
    public static  RightAny rightAny() {
        return (RightAny) INSTANCE;
    }

    public static  Semigroup> rightAny(Semigroup rSemigroup) {
        return RightAny.rightAny().apply(rSemigroup);
    }

    public static  Fn1, Either> rightAny(Semigroup rSemigroup, Either x) {
        return RightAny.rightAny(rSemigroup).apply(x);
    }

    public static  Either rightAny(Semigroup rSemigroup, Either x, Either y) {
        return rightAny(rSemigroup, x).apply(y);
    }
}