GC: completed defining gc functions

gc.c

@@ -0,0 +1,45 @@
+#include <stdlib.h>
+
+#include "gc.h"
+#include "vm.h"
+
+void mark(struct garbageObject *obj) {
+  if (obj->mark) return;
+
+  ++obj->mark;
+
+  if (obj->type == GARBAGE_PAIR) {
+    mark(obj->head);
+    mark(obj->tail);
+  }
+}
+
+void markAll(struct virtualMachine *vm) {
+  for (int i = 0; i < vm->stackSize; ++i) {
+    mark(vm->stack[i]);
+  }
+}
+
+void sweep(struct virtualMachine *vm) {
+  struct garbageObject **obj = &vm->head;
+
+  while (*obj) {
+    if (!(*obj)->mark) {
+      struct garbageObject *unreachable = *obj;
+      *obj = unreachable->next;
+      free(unreachable);
+      vm->refCount--;
+    } else {
+      (*obj)->mark = 0;
+      obj = &(*obj)->next;
+    }
+  }
+}
+
+int collect(struct virtualMachine *vm) {
+  int count = vm->refCount;
+  markAll(vm);
+  sweep(vm);
+  vm->refMax = vm->refCount * 2;
+  return count - vm->refCount;
+}

gc.h

@@ -1,6 +1,8 @@
 #ifndef GC_H
 #define GC_H
 
+#include "vm.h"
+
 // Marks a single reference if it is still in use
 void mark(struct garbageObject *obj);
 
@@ -11,6 +13,6 @@ void markAll(struct virtualMachine *vm);
 void sweep(struct virtualMachine *vm);
 
 // Marks and Sweeps all references
-void collect(struct virtualMachine *vm);
+int collect(struct virtualMachine *vm);
 
 #endif /* GC_H */