[jlox] Interpret superclasses

jlox/lox/src/main/java/xyz/ctsk/lox/Interpreter.java

@@ -80,6 +80,14 @@ public class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
 
     @Override
     public Void visitClassStmt(Stmt.Class stmt) {
+        Object superclass = null;
+        if (stmt.superclass() != null) {
+            superclass = evaluate(stmt.superclass());
+            if (!(superclass instanceof LoxClass)) {
+                throw new RuntimeError(stmt.superclass().name(), "Superclass must be a class.");
+            }
+        }
+
         environment.define(stmt.name().lexeme(), null);
 
         Map<String, LoxFunction> methods = new HashMap<>();
@@ -88,7 +96,7 @@ public class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
             methods.put(method.name().lexeme(), function);
         }
 
-        LoxClass clazz = new LoxClass(stmt.name().lexeme(), methods);
+        LoxClass clazz = new LoxClass(stmt.name().lexeme(), (LoxClass) superclass, methods);
         environment.assign(stmt.name(), clazz);
         return null;
     }

jlox/lox/src/main/java/xyz/ctsk/lox/LoxClass.java

@@ -5,10 +5,12 @@ import java.util.Map;
 
 public class LoxClass implements LoxCallable {
     final String name;
+    private final LoxClass superclass;
     private final Map<String, LoxFunction> methods;
 
-    LoxClass(String name, Map<String, LoxFunction> methods) {
+    LoxClass(String name, LoxClass superclass, Map<String, LoxFunction> methods) {
         this.name = name;
+        this.superclass = superclass;
         this.methods = methods;
     }
 
@@ -39,6 +41,10 @@ public class LoxClass implements LoxCallable {
             return methods.get(name);
         }
 
+        if (superclass != null) {
+            return superclass.findMethod(name);
+        }
+
         return null;
     }
 }