Added class inheritance and constructors. (0.16.0)

examples/inheritance_demo.fun

@@ -0,0 +1,59 @@
+#!/usr/bin/env fun
+
+/*
+ * This file is part of the Fun programming language.
+ * https://hanez.org/project/fun/
+ *
+ * Copyright 2025 Johannes Findeisen <you@hanez.org>
+ * Licensed under the terms of the Apache-2.0 license.
+ * https://opensource.org/license/apache-2-0
+ *
+ * Added: 2025-10-01
+ */
+
+/*
+ * Inheritance demo:
+ * - Child extends Parent
+ * - Parent initializes fields in its constructor
+ * - Child overrides/extends behavior and fields
+ */
+
+print("=== inheritance demo ===")
+
+class Parent(number start)
+  value = 0
+  fun _construct(this, s)
+    this.value = s
+
+  fun describe(this)
+    return "Parent(value=" + to_string(this.value) + ")"
+
+  fun hello(this)
+    return "Hello from Parent()"
+
+class Child(number start) extends Parent
+  bonus = 5
+
+  fun _construct(this, s)
+    // child's constructor runs after parent's fields were merged
+    this.value = this.value + this.bonus
+
+  fun describe(this)
+    return "Child(value=" + to_string(this.value) + ", bonus=" + to_string(this.bonus) + ")"
+
+p = Parent(10)
+print(p.describe())       // expect: Parent(value=10)
+
+c = Child(10)
+print(c.describe())       // expect: Child(value=15, bonus=5)
+print(c.hello())
+
+print("=== done ===")
+
+/* Expected output:
+=== inheritance demo ===
+Parent(value=10)
+Child(value=15, bonus=5)
+Hello from Parent()
+=== done ===
+*/