1 files changed, 201 insertions, 0 deletions
diff --git a/src/main/java/bjc/data/Lazy.java b/src/main/java/bjc/data/Lazy.java
new file mode 100644
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+++ b/src/main/java/bjc/data/Lazy.java
@@ -0,0 +1,201 @@
+package bjc.data;
+
+import java.util.function.Function;
+import java.util.function.Supplier;
+import java.util.function.UnaryOperator;
+
+import bjc.data.internals.BoundLazy;
+import bjc.funcdata.FunctionalList;
+import bjc.funcdata.IList;
+
+/**
+ * A holder that holds a means to create a value, but doesn't actually compute
+ * the value until it's needed.
+ *
+ * @author ben
+ *
+ * @param <ContainedType>
+ *        The type of the value being held.
+ */
+public class Lazy<ContainedType> implements IHolder<ContainedType> {
+	/* The supplier of the type. */
+	private Supplier<ContainedType> valueSupplier;
+	/* The actual type value. */
+	private ContainedType heldValue;
+	/* Whether the value has been created. */
+	private boolean valueMaterialized;
+
+	/* The list of pending actions on the value. */
+	private IList<UnaryOperator<ContainedType>> actions = new FunctionalList<>();
+
+	/**
+	 * Create a new lazy value from the specified seed value.
+	 *
+	 * @param value
+	 *        The seed value to use.
+	 */
+	public Lazy(final ContainedType value) {
+		heldValue = value;
+
+		valueMaterialized = true;
+	}
+
+	/**
+	 * Create a new lazy value from the specified value source.
+	 *
+	 * @param supp
+	 *        The source of a value to use.
+	 */
+	public Lazy(final Supplier<ContainedType> supp) {
+		valueSupplier = new SingleSupplier<>(supp);
+
+		valueMaterialized = false;
+	}
+
+	/* Create a new value from a supplier and a list of actions. */
+	private Lazy(final Supplier<ContainedType> supp, final IList<UnaryOperator<ContainedType>> pendingActions) {
+		valueSupplier = supp;
+
+		actions = pendingActions;
+	}
+
+	@Override
+	public <BoundType> IHolder<BoundType> bind(final Function<ContainedType, IHolder<BoundType>> binder) {
+		final IList<UnaryOperator<ContainedType>> pendingActions = new FunctionalList<>();
+
+		actions.forEach(pendingActions::add);
+
+		final Supplier<ContainedType> supplier = () -> {
+			if(valueMaterialized) return heldValue;
+
+			return valueSupplier.get();
+		};
+
+		return new BoundLazy<>(() -> {
+			return new Lazy<>(supplier, pendingActions);
+		}, binder);
+	}
+
+	@Override
+	public <NewType> Function<ContainedType, IHolder<NewType>> lift(final Function<ContainedType, NewType> func) {
+		return val -> {
+			return new Lazy<>(func.apply(val));
+		};
+	}
+
+	@Override
+	public <MappedType> IHolder<MappedType> map(final Function<ContainedType, MappedType> mapper) {
+		final IList<UnaryOperator<ContainedType>> pendingActions = new FunctionalList<>();
+
+		actions.forEach(pendingActions::add);
+
+		return new Lazy<>(() -> {
+			ContainedType currVal = heldValue;
+
+			if(!valueMaterialized) {
+				currVal = valueSupplier.get();
+			}
+
+			return pendingActions.reduceAux(currVal, UnaryOperator<ContainedType>::apply,
+					value -> mapper.apply(value));
+		});
+	}
+
+	@Override
+	public String toString() {
+		if(valueMaterialized) {
+			if(actions.isEmpty()) {
+				return String.format("value[v='%s']", heldValue);
+			}
+
+			return String.format("value[v='%s'] (has pending transforms)", heldValue);
+		}
+
+		return "(unmaterialized)";
+	}
+
+	@Override
+	public IHolder<ContainedType> transform(final UnaryOperator<ContainedType> transformer) {
+		actions.add(transformer);
+
+		return this;
+	}
+
+	@Override
+	public <UnwrappedType> UnwrappedType unwrap(final Function<ContainedType, UnwrappedType> unwrapper) {
+		if(!valueMaterialized) {
+			heldValue = valueSupplier.get();
+
+			valueMaterialized = true;
+		}
+
+		actions.forEach(action -> {
+			heldValue = action.apply(heldValue);
+		});
+
+		actions = new FunctionalList<>();
+
+		return unwrapper.apply(heldValue);
+	}
+
+	@Override
+	public int hashCode() {
+		final int prime = 31;
+		int result = 1;
+
+		result = prime * result + (actions == null ? 0 : actions.hashCode());
+		result = prime * result + (heldValue == null ? 0 : heldValue.hashCode());
+		result = prime * result + (valueMaterialized ? 1231 : 1237);
+
+		return result;
+	}
+
+	@Override
+	public boolean equals(final Object obj) {
+		if(this == obj) return true;
+		if(obj == null) return false;
+		if(!(obj instanceof Lazy<?>)) return false;
+
+		final Lazy<?> other = (Lazy<?>) obj;
+
+		if(valueMaterialized != other.valueMaterialized) return false;
+
+		if(valueMaterialized) {
+			if(heldValue == null) {
+				if(other.heldValue != null) return false;
+			} else if(!heldValue.equals(other.heldValue)) return false;
+		} else
+			return false;
+
+		if(actions == null) {
+			if(other.actions != null) return false;
+		} else if(actions.getSize() > 0 || other.actions.getSize() > 0) return false;
+
+		return true;
+	}
+
+	/**
+	 * Create a new lazy container with an already present value.
+	 *
+	 * @param val
+	 *        The value for the lazy container.
+	 *
+	 * @return A new lazy container holding that value.
+	 */
+	public static <ContainedType> Lazy<ContainedType> lazy(final ContainedType val) {
+		return new Lazy<>(val);
+	}
+
+	/**
+	 * Create a new lazy container with a suspended value.
+	 *
+	 * @param supp
+	 *        The suspended value for the lazy container.
+	 *
+	 * @return A new lazy container that will un-suspend the value when
+	 *         necessary.
+	 */
+	public static <ContainedType> Lazy<ContainedType> lazy(final Supplier<ContainedType> supp) {
+		return new Lazy<>(supp);
+	}
+}