From 3da4016d5784adef217fff0ad1e3a0ceff76290f Mon Sep 17 00:00:00 2001
From: Tom Willemse
Date: Tue, 22 Mar 2022 17:15:17 -0700
Subject: Chapter 24.7

---
 clox/src/memory.c |  3 +++
 clox/src/object.c |  9 +++++++++
 clox/src/object.h | 11 +++++++++++
 clox/src/vm.c     | 22 ++++++++++++++++++++++
 4 files changed, 45 insertions(+)

diff --git a/clox/src/memory.c b/clox/src/memory.c
index 8f8fd4a..e88b91f 100644
--- a/clox/src/memory.c
+++ b/clox/src/memory.c
@@ -23,6 +23,9 @@ static void freeObject(Obj *object) {
     FREE(ObjFunction, object);
     break;
   }
+  case OBJ_NATIVE:
+    FREE(ObjNative, object);
+    break;
   case OBJ_STRING: {
     ObjString *string = (ObjString *)object;
     FREE_ARRAY(char, string->chars, string->length + 1);
diff --git a/clox/src/object.c b/clox/src/object.c
index 2df533e..d4afccc 100644
--- a/clox/src/object.c
+++ b/clox/src/object.c
@@ -27,6 +27,12 @@ ObjFunction *newFunction() {
   return function;
 }
 
+ObjNative *newNative(NativeFn function) {
+  ObjNative *native = ALLOCATE_OBJ(ObjNative, OBJ_NATIVE);
+  native->function = function;
+  return native;
+}
+
 static ObjString *allocateString(char *chars, int length, uint32_t hash) {
   ObjString *string = ALLOCATE_OBJ(ObjString, OBJ_STRING);
   string->length = length;
@@ -81,6 +87,9 @@ void printObject(Value value) {
   case OBJ_FUNCTION:
     printFunction(AS_FUNCTION(value));
     break;
+  case OBJ_NATIVE:
+    printf("<native fn>");
+    break;
   case OBJ_STRING:
     printf("%s", AS_CSTRING(value));
     break;
diff --git a/clox/src/object.h b/clox/src/object.h
index 812c464..b5942d6 100644
--- a/clox/src/object.h
+++ b/clox/src/object.h
@@ -8,14 +8,17 @@
 #define OBJ_TYPE(value) (AS_OBJ(value)->type)
 
 #define IS_FUNCTION(value) isObjType(value, OBJ_FUNCTION)
+#define IS_NATIVE(value) isObjType(value, OBJ_NATIVE)
 #define IS_STRING(value) isObjType(value, OBJ_STRING)
 
 #define AS_FUNCTION(value) ((ObjFunction *)AS_OBJ(value))
+#define AS_NATIVE(value) (((ObjNative *)AS_OBJ(value))->function)
 #define AS_STRING(value) ((ObjString *)AS_OBJ(value))
 #define AS_CSTRING(value) (((ObjString *)AS_OBJ(value))->chars)
 
 typedef enum {
   OBJ_FUNCTION,
+  OBJ_NATIVE,
   OBJ_STRING,
 } ObjType;
 
@@ -31,6 +34,13 @@ typedef struct {
   ObjString *name;
 } ObjFunction;
 
+typedef Value (*NativeFn)(int argCount, Value *args);
+
+typedef struct {
+  Obj obj;
+  NativeFn function;
+} ObjNative;
+
 struct ObjString {
   Obj obj;
   int length;
@@ -39,6 +49,7 @@ struct ObjString {
 };
 
 ObjFunction *newFunction();
+ObjNative *newNative(NativeFn function);
 ObjString *takeString(char *chars, int length);
 ObjString *copyString(const char *chars, int length);
 void printObject(Value value);
diff --git a/clox/src/vm.c b/clox/src/vm.c
index 0d8d638..bf7078c 100644
--- a/clox/src/vm.c
+++ b/clox/src/vm.c
@@ -1,6 +1,7 @@
 #include <stdarg.h>
 #include <stdio.h>
 #include <string.h>
+#include <time.h>
 
 #include "common.h"
 #include "compiler.h"
@@ -11,6 +12,10 @@
 
 VM vm;
 
+static Value clockNative(int argCount, Value *args) {
+  return NUMBER_VAL((double)clock() / CLOCKS_PER_SEC);
+}
+
 static void resetStack() {
   vm.stackTop = vm.stack;
   vm.frameCount = 0;
@@ -38,12 +43,22 @@ static void runtimeError(const char *format, ...) {
   resetStack();
 }
 
+static void defineNative(const char *name, NativeFn function) {
+  push(OBJ_VAL(copyString(name, (int)strlen(name))));
+  push(OBJ_VAL(newNative(function)));
+  tableSet(&vm.globals, AS_STRING(vm.stack[0]), vm.stack[1]);
+  pop();
+  pop();
+}
+
 void initVM() {
   resetStack();
   vm.objects = NULL;
 
   initTable(&vm.globals);
   initTable(&vm.strings);
+
+  defineNative("clock", clockNative);
 }
 
 void freeVM() {
@@ -88,6 +103,13 @@ static bool callValue(Value callee, int argCount) {
     switch (OBJ_TYPE(callee)) {
     case OBJ_FUNCTION:
       return call(AS_FUNCTION(callee), argCount);
+    case OBJ_NATIVE: {
+      NativeFn native = AS_NATIVE(callee);
+      Value result = native(argCount, vm.stackTop - argCount);
+      vm.stackTop -= argCount + 1;
+      push(result);
+      return true;
+    }
     default:
       break;
     }
-- 
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