13.1 Superclasses and Subclasses

1 files changed, 8 insertions, 1 deletions

diff --git a/src/com/craftinginterpreters/lox/Interpreter.java b/src/com/craftinginterpreters/lox/Interpreter.java
index 7dfd0fb..101c33c 100644
--- a/src/com/craftinginterpreters/lox/Interpreter.java
+++ b/src/com/craftinginterpreters/lox/Interpreter.java
@@ -181,6 +181,13 @@ 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<>();
@@ -189,7 +196,7 @@ class Interpreter implements Expr.Visitor<Object>, Stmt.Visitor<Void> {
             methods.put(method.name.lexeme, function);
         }
 
-        LoxClass klass = new LoxClass(stmt.name.lexeme, methods);
+        LoxClass klass = new LoxClass(stmt.name.lexeme, (LoxClass)superclass, methods);
         environment.assign(stmt.name, klass);
         return null;
     }