2 files changed, 178 insertions, 0 deletions
diff --git a/base/src/main/java/bjc/utils/funcdata/theory/Bifunctor.java b/base/src/main/java/bjc/utils/funcdata/theory/Bifunctor.java
new file mode 100644
index 0000000..13c1709
--- /dev/null
+++ b/base/src/main/java/bjc/utils/funcdata/theory/Bifunctor.java
@@ -0,0 +1,139 @@
+package bjc.utils.funcdata.theory;
+
+import java.util.function.Function;
+
+/**
+ * A functor over a pair of heterogeneous types
+ *
+ * @author ben
+ * @param <LeftType>
+ *                The type stored on the 'left' of the pair
+ * @param <RightType>
+ *                The type stored on the 'right' of the pair
+ *
+ */
+public interface Bifunctor<LeftType, RightType> {
+	/**
+	 * Alias for functor mapping.
+	 *
+	 * @author EVE
+	 *
+	 * @param <OldLeft>
+	 * @param <OldRight>
+	 * @param <NewLeft>
+	 * @param <NewRight>
+	 */
+	public interface BifunctorMap<OldLeft, OldRight, NewLeft, NewRight>
+			extends Function<Bifunctor<OldLeft, OldRight>, Bifunctor<NewLeft, NewRight>> {
+
+	}
+
+	/**
+	 * Alias for left functor mapping.
+	 *
+	 * @author EVE
+	 *
+	 * @param <OldLeft>
+	 * @param <OldRight>
+	 * @param <NewLeft>
+	 */
+	public interface LeftBifunctorMap<OldLeft, OldRight, NewLeft>
+			extends BifunctorMap<OldLeft, OldRight, NewLeft, OldRight> {
+
+	}
+
+	/**
+	 * Alias for right functor mapping.
+	 *
+	 * @author EVE
+	 *
+	 * @param <OldLeft>
+	 * @param <OldRight>
+	 * @param <NewRight>
+	 */
+	public interface RightBifunctorMap<OldLeft, OldRight, NewRight>
+			extends BifunctorMap<OldLeft, OldRight, OldLeft, NewRight> {
+
+	}
+
+	/**
+	 * Lift a pair of functions to a single function that maps over both
+	 * parts of a pair
+	 *
+	 * @param <OldLeft>
+	 *                The old left type of the pair
+	 * @param <OldRight>
+	 *                The old right type of the pair
+	 * @param <NewLeft>
+	 *                The new left type of the pair
+	 * @param <NewRight>
+	 *                The new right type of the pair
+	 * @param leftFunc
+	 *                The function that maps over the left of the pair
+	 * @param rightFunc
+	 *                The function that maps over the right of the pair
+	 * @return A function that maps over both parts of the pair
+	 */
+	public default <OldLeft, OldRight, NewLeft, NewRight> BifunctorMap<OldLeft, OldRight, NewLeft, NewRight> bimap(
+			final Function<OldLeft, NewLeft> leftFunc, final Function<OldRight, NewRight> rightFunc) {
+		final BifunctorMap<OldLeft, OldRight, NewLeft, NewRight> bimappedFunc = (argPair) -> {
+			final LeftBifunctorMap<OldLeft, OldRight, NewLeft> leftMapper = argPair.fmapLeft(leftFunc);
+
+			final Bifunctor<NewLeft, OldRight> leftMappedFunctor = leftMapper.apply(argPair);
+			final RightBifunctorMap<NewLeft, OldRight, NewRight> rightMapper = leftMappedFunctor
+					.fmapRight(rightFunc);
+
+			return rightMapper.apply(leftMappedFunctor);
+		};
+
+		return bimappedFunc;
+	}
+
+	/**
+	 * Lift a function to operate over the left part of this pair
+	 *
+	 * @param <OldLeft>
+	 *                The old left type of the pair
+	 * @param <OldRight>
+	 *                The old right type of the pair
+	 * @param <NewLeft>
+	 *                The new left type of the pair
+	 * @param func
+	 *                The function to lift to work over the left side of the
+	 *                pair
+	 * @return The function lifted to work over the left side of bifunctors
+	 */
+	public <OldLeft, OldRight, NewLeft> LeftBifunctorMap<OldLeft, OldRight, NewLeft> fmapLeft(
+			Function<OldLeft, NewLeft> func);
+
+	/**
+	 * Lift a function to operate over the right part of this pair
+	 *
+	 * @param <OldLeft>
+	 *                The old left type of the pair
+	 * @param <OldRight>
+	 *                The old right type of the pair
+	 * @param <NewRight>
+	 *                The new right type of the pair
+	 * @param func
+	 *                The function to lift to work over the right side of
+	 *                the pair
+	 * @return The function lifted to work over the right side of bifunctors
+	 */
+	public <OldLeft, OldRight, NewRight> RightBifunctorMap<OldLeft, OldRight, NewRight> fmapRight(
+			Function<OldRight, NewRight> func);
+
+	/**
+	 * Get the value contained on the left of this bifunctor
+	 *
+	 * @return The value on the left side of this bifunctor
+	 */
+	public LeftType getLeft();
+
+	/**
+	 * Get the value contained on the right of this bifunctor
+	 *
+	 * @return The value on the right of this bifunctor
+	 */
+	public RightType getRight();
+}
diff --git a/base/src/main/java/bjc/utils/funcdata/theory/Functor.java b/base/src/main/java/bjc/utils/funcdata/theory/Functor.java
new file mode 100644
index 0000000..1c53284
--- /dev/null
+++ b/base/src/main/java/bjc/utils/funcdata/theory/Functor.java
@@ -0,0 +1,39 @@
+package bjc.utils.funcdata.theory;
+
+import java.util.function.Function;
+
+/**
+ * Represents a container or context some sort usually, but the precise
+ * definition is that it represents exactly what it is defined as
+ *
+ * @author ben
+ * @param <ContainedType>
+ *                The value inside the functor
+ */
+public interface Functor<ContainedType> {
+	/**
+	 * Converts a normal function to operate over values in a functor.
+	 *
+	 * N.B: Even though the type signature implies that you can apply the
+	 * resulting function to any type of functor, it is only safe to call it
+	 * on instances of the type of functor you called fmap on.
+	 *
+	 * @param <ArgType>
+	 *                The argument of the function
+	 * @param <ReturnType>
+	 *                The return type of the function
+	 * @param func
+	 *                The function to convert
+	 * @return The passed in function converted to work over a particular
+	 *         type of functors
+	 */
+	public <ArgType, ReturnType> Function<Functor<ArgType>, Functor<ReturnType>> fmap(
+			Function<ArgType, ReturnType> func);
+
+	/**
+	 * Retrieve the thing inside this functor
+	 *
+	 * @return The thing inside this functor
+	 */
+	public ContainedType getValue();
+}