Add Void: a logically uninhabited data type. Fix #193

jbgi · jbgi · commit 71c637bd35aa · 2015-12-10T21:22:15.000+01:00
diff --git a/core/src/main/java/fj/Void.java b/core/src/main/java/fj/Void.java
@@ -0,0 +1,16 @@
+package fj;
+
+/**
+ * A logically uninhabited data type.
+ */
+public abstract class Void {
+
+  private Void() {
+    throw new IllegalStateException("Void cannot be instantiated");
+  }
+
+  /**
+   * Since Void values logically don't exist, this witnesses the logical reasoning tool of "ex falso quodlibet".
+   */
+  public abstract <X> X absurd();
+}
