[jlox] Parse superclass

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

@@ -14,7 +14,8 @@ import static xyz.ctsk.lox.TokenType.*;
  *                | funDecl
  *                | varDecl
  *                | statement ;
- * classDecl      → "class" IDENTIFIER "{" function* "}" ;
+ * classDecl      → "class" IDENTIFIER ( "<" IDENTIFIER )?
+ *                  "{" function* "}" ;
  * funDecl        → "fun" function ;
  * function       → IDENTIFIER "(" parameters? ")" block ;
  * parameters     → IDENTIFIER ( "," IDENTIFIER )* ;
@@ -87,6 +88,13 @@ public class Parser {
 
     private Stmt classDeclaration() {
         var name = consume(IDENTIFIER, "Expect class name.");
+
+        Expr.Variable superclass = null;
+        if (match(LESS)) {
+            consume(IDENTIFIER, "Expect superclass name.");
+            superclass = new Expr.Variable(previous());
+        }
+
         consume(LEFT_BRACE, "Expect '{' before class body.");
 
         List<Stmt.Function> methods = new ArrayList<>();
@@ -96,8 +104,7 @@ public class Parser {
         }
 
         consume(LEFT_BRACE, "Expect '}' after class body.");
-        return new Stmt.Class(name, methods);
-
+        return new Stmt.Class(name, superclass, methods);
     }
 
     private Stmt.Function function(FunctionType kind) {

jlox/lox/src/main/java/xyz/ctsk/lox/package-info.java

@@ -16,7 +16,7 @@
         @Root(name = "Stmt",
                 rules = {
                         @Rule(head = "Block", body = {"List<Stmt> statements"}),
-                        @Rule(head = "Class", body = {"Token name", "List<Stmt.Function> methods"}),
+                        @Rule(head = "Class", body = {"Token name", "Expr.Variable superclass", "List<Stmt.Function> methods"}),
                         @Rule(head = "Expression", body = {"Expr expression"}),
                         @Rule(head = "Function", body = {"Token name", "List<Token> params", "List<Stmt> body"}),
                         @Rule(head = "If", body = {"Expr condition", "Stmt thenBranch", "Stmt elseBranch"}),