From 73dfe7efa53b5ed58b9e1e94dceec14ec19d6308 Mon Sep 17 00:00:00 2001
From: Tom Willemse
Date: Tue, 27 Jul 2021 22:21:40 -0700
Subject: Chapter 15.2

---
 clox/src/vm.c | 30 +++++++++++++++++++++++++++---
 clox/src/vm.h |  7 +++++++
 2 files changed, 34 insertions(+), 3 deletions(-)

(limited to 'clox')

diff --git a/clox/src/vm.c b/clox/src/vm.c
index 14a206e..ffd207d 100644
--- a/clox/src/vm.c
+++ b/clox/src/vm.c
@@ -6,16 +6,39 @@
 
 VM vm;
 
-void initVM() {}
+static void resetStack() {
+  vm.stackTop = vm.stack;
+}
+
+void initVM() {
+  resetStack();
+}
 
 void freeVM() {}
 
+void push(Value value) {
+  *vm.stackTop = value;
+  vm.stackTop++;
+}
+
+Value pop() {
+  vm.stackTop--;
+  return *vm.stackTop;
+}
+
 static InterpretResult run() {
 #define READ_BYTE() (*vm.ip++)
 #define READ_CONSTANT() (vm.chunk->constants.values[READ_BYTE()])
 
   for (;;) {
 #ifdef DEBUG_TRACE_EXECUTION
+    printf("          ");
+    for (Value *slot = vm.stack; slot < vm.stackTop; slot++) {
+      printf("[ ");
+      printValue(*slot);
+      printf(" ]");
+    }
+    printf("\n");
     disassembleInstruction(vm.chunk, (int)(vm.ip - vm.chunk->code));
 #endif
 
@@ -23,11 +46,12 @@ static InterpretResult run() {
     switch (instruction = READ_BYTE()) {
     case OP_CONSTANT: {
       Value constant = READ_CONSTANT();
-      printValue(constant);
-      printf("\n");
+      push(constant);
       break;
     }
     case OP_RETURN: {
+      printValue(pop());
+      printf("\n");
       return INTERPRET_OK;
     }
     }
diff --git a/clox/src/vm.h b/clox/src/vm.h
index d11ae70..2585bd2 100644
--- a/clox/src/vm.h
+++ b/clox/src/vm.h
@@ -2,10 +2,15 @@
 #define clox_vm_h
 
 #include "chunk.h"
+#include "value.h"
+
+#define STACK_MAX 256
 
 typedef struct {
   Chunk *chunk;
   uint8_t *ip;
+  Value stack[STACK_MAX];
+  Value* stackTop;
 } VM;
 
 typedef enum {
@@ -17,5 +22,7 @@ typedef enum {
 void initVM();
 void freeVM();
 InterpretResult interpret(Chunk *chunk);
+void push(Value value);
+Value pop();
 
 #endif
-- 
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