From 37ac05af6d0aa57ccc5ea805af262a407fedeeae Mon Sep 17 00:00:00 2001
From: Tom Willemse
Date: Wed, 12 Jan 2022 23:09:36 -0800
Subject: Chapter 23.3

---
 clox/src/chunk.h    |  1 +
 clox/src/compiler.c | 28 ++++++++++++++++++++++++++++
 clox/src/debug.c    |  2 ++
 clox/src/vm.c       |  5 +++++
 4 files changed, 36 insertions(+)

(limited to 'clox')

diff --git a/clox/src/chunk.h b/clox/src/chunk.h
index db524cf..2ec7a8d 100644
--- a/clox/src/chunk.h
+++ b/clox/src/chunk.h
@@ -27,6 +27,7 @@ typedef enum {
   OP_PRINT,
   OP_JUMP,
   OP_JUMP_IF_FALSE,
+  OP_LOOP,
   OP_RETURN,
 } OpCode;
 
diff --git a/clox/src/compiler.c b/clox/src/compiler.c
index d965f45..beda5d5 100644
--- a/clox/src/compiler.c
+++ b/clox/src/compiler.c
@@ -119,6 +119,17 @@ static void emitBytes(uint8_t byte1, uint8_t byte2) {
   emitByte(byte2);
 }
 
+static void emitLoop(int loopStart) {
+  emitByte(OP_LOOP);
+
+  int offset = currentChunk()->count - loopStart + 2;
+  if (offset > UINT16_MAX)
+    error("Loop body too large.");
+
+  emitByte((offset >> 8) & 0xff);
+  emitByte(offset & 0xff);
+}
+
 static int emitJump(uint8_t instruction) {
   emitByte(instruction);
   emitByte(0xff);
@@ -302,6 +313,21 @@ static void printStatement() {
   emitByte(OP_PRINT);
 }
 
+static void whileStatement() {
+  int loopStart = currentChunk()->count;
+  consume(TOKEN_LEFT_PAREN, "Expect '(' after 'while'.");
+  expression();
+  consume(TOKEN_RIGHT_PAREN, "Expect ')' after condition.");
+
+  int exitJump = emitJump(OP_JUMP_IF_FALSE);
+  emitByte(OP_POP);
+  statement();
+  emitLoop(loopStart);
+
+  patchJump(exitJump);
+  emitByte(OP_POP);
+}
+
 static void synchronize() {
   parser.panicMode = false;
 
@@ -342,6 +368,8 @@ static void statement() {
     printStatement();
   } else if (match(TOKEN_IF)) {
     ifStatement();
+  } else if (match(TOKEN_WHILE)) {
+    whileStatement();
   } else if (match(TOKEN_LEFT_BRACE)) {
     beginScope();
     block();
diff --git a/clox/src/debug.c b/clox/src/debug.c
index b3f756a..3f3c289 100644
--- a/clox/src/debug.c
+++ b/clox/src/debug.c
@@ -92,6 +92,8 @@ int disassembleInstruction(Chunk *chunk, int offset) {
     return jumpInstruction("OP_JUMP", 1, chunk, offset);
   case OP_JUMP_IF_FALSE:
     return jumpInstruction("OP_JUMP_IF_FALSE", 1, chunk, offset);
+  case OP_LOOP:
+    return jumpInstruction("OP_LOOP", -1, chunk, offset);
   case OP_RETURN:
     return simpleInstruction("OP_RETURN", offset);
   default:
diff --git a/clox/src/vm.c b/clox/src/vm.c
index 49a162d..c1c6941 100644
--- a/clox/src/vm.c
+++ b/clox/src/vm.c
@@ -211,6 +211,11 @@ static InterpretResult run() {
         vm.ip += offset;
       break;
     }
+    case OP_LOOP: {
+      uint16_t offset = READ_SHORT();
+      vm.ip -= offset;
+      break;
+    }
     case OP_RETURN: {
       /* The book said to remove this, but when I do I get an infinite loop and
          then a segfault because it keeps trying to add the constant 1 to the
-- 
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