5

Author: igr

java/src/main/java/v/o/i/d/monadsplain/Five.java

@@ -0,0 +1,52 @@
+package v.o.i.d.monadsplain;
+
+import java.util.Arrays;
+import java.util.function.Function;
+import java.util.stream.Stream;
+
+public class Five {
+	public static class IntegerWithHistory {
+		public final Integer value;
+		public final String[] history;
+
+		public IntegerWithHistory(Integer value, String... history) {
+			this.value = value;
+			this.history = history;
+		}
+
+		public static IntegerWithHistory wrap(Integer i) {
+			return new IntegerWithHistory(i);
+		}
+	}
+
+	public IntegerWithHistory calculate(IntegerWithHistory i, Function<Integer, IntegerWithHistory> operation) {
+		final IntegerWithHistory a = operation.apply(i.value);
+		return new IntegerWithHistory(
+				a.value,
+				join(i.history, join(i.history, a.history))
+		);
+	}
+
+	public void run() {
+		Function<Integer, IntegerWithHistory> addOne = i -> new IntegerWithHistory(i + 1, "addOne: " + i);
+		Function<Integer, IntegerWithHistory> square = i -> new IntegerWithHistory(i * i, "square: " + i);
+		IntegerWithHistory i = calculate(
+				calculate(IntegerWithHistory.wrap(3), square),
+				addOne);
+		System.out.println(i.value);
+		System.out.println(Arrays.toString(i.history));
+	}
+
+	public static void main(String[] args) {
+		new Three().run();
+	}
+
+	private static String[] join(String[] array, String element) {
+		return Stream.concat(Arrays.stream(array), Stream.of(element)).toArray(String[]::new);
+	}
+
+	private static String[] join(String[] array, String[] elements) {
+		return Stream.concat(Arrays.stream(array), Stream.of(elements)).toArray(String[]::new);
+	}
+
+}