Add a whole bunch of Optics

This adds a whole bunch of types/functions related to optics. With this
batch, I've mainly gone for the concrete representation types, instead
of var Laarhoven or profunctor representations.

The concrete ones require less infrastructure, though they are not as
easy to compose

There's also a number of misc. things in here

1 files changed, 46 insertions, 0 deletions

diff --git a/src/main/java/bjc/optics/MutableLens.java b/src/main/java/bjc/optics/MutableLens.java
new file mode 100644
index 0000000..88eca04
--- /dev/null
+++ b/src/main/java/bjc/optics/MutableLens.java
@@ -0,0 +1,46 @@
+/* 
+ * esodata - data structures and other things, of varying utility
+ * Copyright 2022, Ben Culkin
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *   
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package bjc.optics;
+
+/**
+ * A type-invariant lens for mutating objects.
+ * 
+ * Note that there is no type-variant version, because that wouldn't make much sense.
+ * 
+ * Also, mixing mutable and immutable lenses may lead to confusion.
+ * 
+ * @author bjcul
+ *
+ * @param <Whole> The type the lens is used on
+ * @param <Part> The type the lens is focused on
+ */
+public interface MutableLens<Whole, Part> extends Lens<Whole, Part> {
+	/**
+	 * Apply a mutation to an item.
+	 * 
+	 * @param source The item to use the lens on.
+	 * @param val The new value for the focused field.
+	 */
+	void mutate(Whole source, Part val);
+	
+	@Override
+	default Whole set(Whole source, Part val) {
+		mutate(source, val);
+		return source;
+	}
+}