1 files changed, 191 insertions, 0 deletions
diff --git a/src/main/java/bjc/data/Either.java b/src/main/java/bjc/data/Either.java
new file mode 100644
index 0000000..0588496
--- /dev/null
+++ b/src/main/java/bjc/data/Either.java
@@ -0,0 +1,191 @@
+package bjc.data;
+
+import java.util.function.BiFunction;
+import java.util.function.Function;
+
+/**
+ * Represents a pair where only one side has a value.
+ *
+ * @author ben
+ *
+ * @param <LeftType>
+ *        The type that could be on the left.
+ *
+ * @param <RightType>
+ *        The type that could be on the right.
+ *
+ */
+public class Either<LeftType, RightType> implements IPair<LeftType, RightType> {
+	/**
+	 * Create a new either with the left value occupied.
+	 *
+	 * @param <LeftType>
+	 *        The type of the left value.
+	 *
+	 * @param <RightType>
+	 *        The type of the empty right value.
+	 * 
+	 * @param left
+	 *        The value to put on the left.
+	 *
+	 * @return An either with the left side occupied.
+	 */
+	public static <LeftType, RightType> Either<LeftType, RightType> left(final LeftType left) {
+		return new Either<>(left, null);
+	}
+
+	/**
+	 * Create a new either with the right value occupied.
+	 *
+	 * @param <LeftType>
+	 *        The type of the empty left value.
+	 *
+	 * @param <RightType>
+	 *        The type of the right value.
+	 *
+	 * @param right
+	 *        The value to put on the right.
+	 *
+	 * @return An either with the right side occupied.
+	 */
+	public static <LeftType, RightType> Either<LeftType, RightType> right(final RightType right) {
+		return new Either<>(null, right);
+	}
+
+	/* The left value of the either. */
+	private LeftType leftVal;
+	/* The right value of the either. */
+	private RightType rightVal;
+	/* Whether the left value is the one filled out. */
+	private boolean isLeft;
+
+	/* Create a new either with specifed values. */
+	private Either(final LeftType left, final RightType right) {
+		if(left == null) {
+			rightVal = right;
+		} else {
+			leftVal = left;
+
+			isLeft = true;
+		}
+	}
+
+	@Override
+	public <BoundLeft, BoundRight> IPair<BoundLeft, BoundRight> bind(
+			final BiFunction<LeftType, RightType, IPair<BoundLeft, BoundRight>> binder) {
+		if(binder == null) throw new NullPointerException("Binder must not be null");
+
+		return binder.apply(leftVal, rightVal);
+	}
+
+	@Override
+	public <BoundLeft> IPair<BoundLeft, RightType> bindLeft(
+			final Function<LeftType, IPair<BoundLeft, RightType>> leftBinder) {
+		if(leftBinder == null) throw new NullPointerException("Left binder must not be null");
+
+		if(isLeft) return leftBinder.apply(leftVal);
+
+		return new Either<>(null, rightVal);
+	}
+
+	@Override
+	public <BoundRight> IPair<LeftType, BoundRight> bindRight(
+			final Function<RightType, IPair<LeftType, BoundRight>> rightBinder) {
+		if(rightBinder == null) throw new NullPointerException("Right binder must not be null");
+
+		if(isLeft) return new Either<>(leftVal, null);
+
+		return rightBinder.apply(rightVal);
+	}
+
+	@Override
+	public <OtherLeft, OtherRight, CombinedLeft, CombinedRight> IPair<CombinedLeft, CombinedRight> combine(
+			final IPair<OtherLeft, OtherRight> otherPair,
+			final BiFunction<LeftType, OtherLeft, CombinedLeft> leftCombiner,
+			final BiFunction<RightType, OtherRight, CombinedRight> rightCombiner) {
+		if(otherPair == null) {
+			throw new NullPointerException("Other pair must not be null");
+		} else if(leftCombiner == null) {
+			throw new NullPointerException("Left combiner must not be null");
+		} else if(rightCombiner == null) {
+			throw new NullPointerException("Right combiner must not be null");
+		}
+
+		if(isLeft) {
+			return otherPair.bind((otherLeft, otherRight) -> {
+				CombinedLeft cLeft = leftCombiner.apply(leftVal, otherLeft);
+
+				return new Either<>(cLeft, null);
+			});
+		}
+
+		return otherPair.bind((otherLeft, otherRight) -> {
+			CombinedRight cRight = rightCombiner.apply(rightVal, otherRight);
+
+			return new Either<>(null, cRight);
+		});
+	}
+
+	@Override
+	public <NewLeft> IPair<NewLeft, RightType> mapLeft(final Function<LeftType, NewLeft> mapper) {
+		if(mapper == null) throw new NullPointerException("Mapper must not be null");
+
+		if(isLeft) return new Either<>(mapper.apply(leftVal), null);
+
+		return new Either<>(null, rightVal);
+	}
+
+	@Override
+	public <NewRight> IPair<LeftType, NewRight> mapRight(final Function<RightType, NewRight> mapper) {
+		if(mapper == null) throw new NullPointerException("Mapper must not be null");
+
+		if(isLeft) return new Either<>(leftVal, null);
+
+		return new Either<>(null, mapper.apply(rightVal));
+	}
+
+	@Override
+	public <MergedType> MergedType merge(final BiFunction<LeftType, RightType, MergedType> merger) {
+		if(merger == null) throw new NullPointerException("Merger must not be null");
+
+		return merger.apply(leftVal, rightVal);
+	}
+
+	@Override
+	public int hashCode() {
+		final int prime = 31;
+
+		int result = 1;
+		result = prime * result + (isLeft ? 1231 : 1237);
+		result = prime * result + (leftVal == null ? 0 : leftVal.hashCode());
+		result = prime * result + (rightVal == null ? 0 : rightVal.hashCode());
+
+		return result;
+	}
+
+	@Override
+	public boolean equals(final Object obj) {
+		if(this == obj) return true;
+		if(obj == null) return false;
+		if(!(obj instanceof Either<?, ?>)) return false;
+
+		final Either<?, ?> other = (Either<?, ?>) obj;
+
+		if(isLeft != other.isLeft) return false;
+
+		if(leftVal == null) {
+			if(other.leftVal != null) return false;
+		} else if(!leftVal.equals(other.leftVal)) return false;
+
+		if(rightVal == null) {
+			if(other.rightVal != null) return false;
+		} else if(!rightVal.equals(other.rightVal)) return false;
+
+		return true;
+	}
+
+	@Override
+	public String toString() {
+		return String.format("Either [leftVal='%s', rightVal='%s', isLeft=%s]", leftVal, rightVal, isLeft);
+	}
+}