1 files changed, 249 insertions, 0 deletions
diff --git a/src/main/java/bjc/data/LazyPair.java b/src/main/java/bjc/data/LazyPair.java
new file mode 100644
index 0000000..1633c65
--- /dev/null
+++ b/src/main/java/bjc/data/LazyPair.java
@@ -0,0 +1,249 @@
+package bjc.data;
+
+import java.util.function.BiFunction;
+import java.util.function.Function;
+import java.util.function.Supplier;
+
+import bjc.data.internals.BoundLazyPair;
+import bjc.data.internals.HalfBoundLazyPair;
+
+/**
+ * A lazy implementation of a pair.
+ *
+ * @author ben
+ *
+ * @param <LeftType>
+ *        The type on the left side of the pair.
+ *
+ * @param <RightType>
+ *        The type on the right side of the pair.
+ */
+public class LazyPair<LeftType, RightType> implements IPair<LeftType, RightType> {
+	/* The supplier for the left value. */
+	private Supplier<LeftType> leftSupplier;
+	/* The left value. */
+	private LeftType leftValue;
+	/* Whether the left value has been created. */
+	private boolean leftMaterialized;
+
+	/* The supplier for the right value. */
+	private Supplier<RightType> rightSupplier;
+	/* The right value. */
+	private RightType rightValue;
+	/* Whether the right value has been created. */
+	private boolean rightMaterialized;
+
+	/**
+	 * Create a new lazy pair, using the set values.
+	 *
+	 * @param leftVal
+	 *        The value for the left side of the pair.
+	 *
+	 * @param rightVal
+	 *        The value for the right side of the pair.
+	 */
+	public LazyPair(final LeftType leftVal, final RightType rightVal) {
+		leftValue = leftVal;
+		rightValue = rightVal;
+
+		leftMaterialized = true;
+		rightMaterialized = true;
+	}
+
+	/**
+	 * Create a new lazy pair from the given value sources.
+	 *
+	 * @param leftSupp
+	 *        The source for a value on the left side of the pair.
+	 *
+	 * @param rightSupp
+	 *        The source for a value on the right side of the pair.
+	 */
+	public LazyPair(final Supplier<LeftType> leftSupp, final Supplier<RightType> rightSupp) {
+		/* Use single suppliers to catch double-instantiation bugs. */
+		leftSupplier = new SingleSupplier<>(leftSupp);
+		rightSupplier = new SingleSupplier<>(rightSupp);
+
+		leftMaterialized = false;
+		rightMaterialized = false;
+	}
+
+	@Override
+	public <BoundLeft, BoundRight> IPair<BoundLeft, BoundRight> bind(
+			final BiFunction<LeftType, RightType, IPair<BoundLeft, BoundRight>> binder) {
+		return new BoundLazyPair<>(leftSupplier, rightSupplier, binder);
+	}
+
+	@Override
+	public <BoundLeft> IPair<BoundLeft, RightType> bindLeft(
+			final Function<LeftType, IPair<BoundLeft, RightType>> leftBinder) {
+		final Supplier<LeftType> leftSupp = () -> {
+			if(leftMaterialized) return leftValue;
+
+			return leftSupplier.get();
+		};
+
+		return new HalfBoundLazyPair<>(leftSupp, leftBinder);
+	}
+
+	@Override
+	public <BoundRight> IPair<LeftType, BoundRight> bindRight(
+			final Function<RightType, IPair<LeftType, BoundRight>> rightBinder) {
+		final Supplier<RightType> rightSupp = () -> {
+			if(rightMaterialized) return rightValue;
+
+			return rightSupplier.get();
+		};
+
+		return new HalfBoundLazyPair<>(rightSupp, rightBinder);
+	}
+
+	@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) {
+		return otherPair.bind((otherLeft, otherRight) -> {
+			return bind((leftVal, rightVal) -> {
+				final CombinedLeft left = leftCombiner.apply(leftVal, otherLeft);
+				final CombinedRight right = rightCombiner.apply(rightVal, otherRight);
+
+				return new LazyPair<>(left, right);
+			});
+		});
+	}
+
+	@Override
+	public LeftType getLeft() {
+		if(!leftMaterialized) {
+			leftValue = leftSupplier.get();
+
+			leftMaterialized = true;
+		}
+
+		return leftValue;
+	}
+
+	@Override
+	public RightType getRight() {
+		if(!rightMaterialized) {
+			rightValue = rightSupplier.get();
+
+			rightMaterialized = true;
+		}
+
+		return rightValue;
+	}
+
+	@Override
+	public <NewLeft> IPair<NewLeft, RightType> mapLeft(final Function<LeftType, NewLeft> mapper) {
+		final Supplier<NewLeft> leftSupp = () -> {
+			if(leftMaterialized) return mapper.apply(leftValue);
+
+			return mapper.apply(leftSupplier.get());
+		};
+
+		final Supplier<RightType> rightSupp = () -> {
+			if(rightMaterialized) return rightValue;
+
+			return rightSupplier.get();
+		};
+
+		return new LazyPair<>(leftSupp, rightSupp);
+	}
+
+	@Override
+	public <NewRight> IPair<LeftType, NewRight> mapRight(final Function<RightType, NewRight> mapper) {
+		final Supplier<LeftType> leftSupp = () -> {
+			if(leftMaterialized) return leftValue;
+
+			return leftSupplier.get();
+		};
+
+		final Supplier<NewRight> rightSupp = () -> {
+			if(rightMaterialized) return mapper.apply(rightValue);
+
+			return mapper.apply(rightSupplier.get());
+		};
+
+		return new LazyPair<>(leftSupp, rightSupp);
+	}
+
+	@Override
+	public <MergedType> MergedType merge(final BiFunction<LeftType, RightType, MergedType> merger) {
+		if(!leftMaterialized) {
+			leftValue = leftSupplier.get();
+
+			leftMaterialized = true;
+		}
+
+		if(!rightMaterialized) {
+			rightValue = rightSupplier.get();
+
+			rightMaterialized = true;
+		}
+
+		return merger.apply(leftValue, rightValue);
+	}
+
+	@Override
+	public String toString() {
+		String leftVal;
+		String rightVal;
+
+		if(leftMaterialized) {
+			leftVal = leftValue.toString();
+		} else {
+			leftVal = "(un-materialized)";
+		}
+
+		if(rightMaterialized) {
+			rightVal = rightValue.toString();
+		} else {
+			rightVal = "(un-materialized)";
+		}
+
+		return String.format("pair[l=%s,r=%s]", leftVal, rightVal);
+	}
+
+	@Override
+	public int hashCode() {
+		final int prime = 31;
+		int result = 1;
+
+		result = prime * result + (leftMaterialized ? 1231 : 1237);
+		result = prime * result + (leftValue == null ? 0 : leftValue.hashCode());
+		result = prime * result + (rightMaterialized ? 1231 : 1237);
+		result = prime * result + (rightValue == null ? 0 : rightValue.hashCode());
+
+		return result;
+	}
+
+	@Override
+	public boolean equals(final Object obj) {
+		if(this == obj) return true;
+		if(obj == null) return false;
+		if(!(obj instanceof LazyPair<?, ?>)) return false;
+
+		final LazyPair<?, ?> other = (LazyPair<?, ?>) obj;
+
+		if(leftMaterialized != other.leftMaterialized) return false;
+
+		if(leftMaterialized) {
+			if(leftValue == null) {
+				if(other.leftValue != null) return false;
+			} else if(!leftValue.equals(other.leftValue)) return false;
+		} else
+			return false;
+
+		if(rightMaterialized != other.rightMaterialized) return false;
+		if(rightMaterialized) {
+			if(rightValue == null) {
+				if(other.rightValue != null) return false;
+			} else if(!rightValue.equals(other.rightValue)) return false;
+		} else
+			return false;
+
+		return true;
+	}
+}