From 726803c9d0c84bccc1d82d1c8aeadfc711752622 Mon Sep 17 00:00:00 2001
From: Tom Willemse
Date: Sun, 14 Aug 2022 20:14:43 -0700
Subject: Chapter 29.1

---
 clox/src/chunk.h    |  1 +
 clox/src/compiler.c | 20 ++++++++++++++++----
 clox/src/debug.c    |  2 ++
 clox/src/vm.c       | 11 +++++++++++
 4 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/clox/src/chunk.h b/clox/src/chunk.h
index 690fffd..4810f38 100644
--- a/clox/src/chunk.h
+++ b/clox/src/chunk.h
@@ -38,6 +38,7 @@ typedef enum {
   OP_CLOSE_UPVALUE,
   OP_RETURN,
   OP_CLASS,
+  OP_INHERIT,
   OP_METHOD,
 } OpCode;
 
diff --git a/clox/src/compiler.c b/clox/src/compiler.c
index bfa0a96..f14666c 100644
--- a/clox/src/compiler.c
+++ b/clox/src/compiler.c
@@ -474,6 +474,10 @@ static void namedVariable(Token name, bool canAssign) {
   }
 }
 
+static void variable(bool canAssign) {
+  namedVariable(parser.previous, canAssign);
+}
+
 static void classDeclaration() {
   consume(TOKEN_IDENTIFIER, "Expect class name");
   Token className = parser.previous;
@@ -487,6 +491,18 @@ static void classDeclaration() {
   classCompiler.enclosing = currentClass;
   currentClass = &classCompiler;
 
+  if (match(TOKEN_LESS)) {
+    consume(TOKEN_IDENTIFIER, "Expect superclass name.");
+    variable(false);
+
+    if (identifiersEqual(&className, &parser.previous)) {
+      error("A class can't inherit from itself.");
+    }
+
+    namedVariable(className, false);
+    emitByte(OP_INHERIT);
+  }
+
   namedVariable(className, false);
   consume(TOKEN_LEFT_BRACE, "Expect '{' before class body.");
   while (!check(TOKEN_RIGHT_BRACE) && !check(TOKEN_EOF)) {
@@ -722,10 +738,6 @@ static void string(bool canAssign) {
       copyString(parser.previous.start + 1, parser.previous.length - 2)));
 }
 
-static void variable(bool canAssign) {
-  namedVariable(parser.previous, canAssign);
-}
-
 static void this_(bool canAssign) {
   if (currentClass == NULL) {
     error("Can't use 'this' outside of a class.");
diff --git a/clox/src/debug.c b/clox/src/debug.c
index 079f0e9..4a39811 100644
--- a/clox/src/debug.c
+++ b/clox/src/debug.c
@@ -139,6 +139,8 @@ int disassembleInstruction(Chunk *chunk, int offset) {
     return simpleInstruction("OP_RETURN", offset);
   case OP_CLASS:
     return constantInstruction("OP_CLASS", chunk, offset);
+  case OP_INHERIT:
+    return simpleInstruction("OP_INHERIT", offset);
   case OP_METHOD:
     return constantInstruction("OP_METHOD", chunk, offset);
   default:
diff --git a/clox/src/vm.c b/clox/src/vm.c
index b5cb1cc..8a6847e 100644
--- a/clox/src/vm.c
+++ b/clox/src/vm.c
@@ -496,6 +496,17 @@ static InterpretResult run() {
     case OP_CLASS:
       push(OBJ_VAL(newClass(READ_STRING())));
       break;
+    case OP_INHERIT: {
+      Value superclass = peek(1);
+      if (!IS_CLASS(superclass)) {
+        runtimeError("Superclass must be a class.");
+        return INTERPRET_RUNTIME_ERROR;
+      }
+      ObjClass *subclass = AS_CLASS(peek(0));
+      tableAddAll(&AS_CLASS(superclass)->methods, &subclass->methods);
+      pop(); /* Subclass. */
+      break;
+    }
     case OP_METHOD:
       defineMethod(READ_STRING());
       break;
-- 
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