lisp: split memory into conses and vectors

During garbage collection, we'll iterate through these two vectors.
Instead of freeing the memory, we can swap cells in the vector and
decrement its size.

The idea is we can attach an allocator to the system where we reuse
memory instead of just allocating everytime.

src/lisp.c

@@ -19,31 +19,57 @@ void sys_init(sys_t *sys)
 void sys_register(sys_t *sys, lisp_t *ptr)
 {
   // Simply append it to the list of currently active conses
-  vec_append(&sys->memory, &ptr, sizeof(&ptr));
+  switch (get_tag(ptr))
+  {
+  case TAG_CONS:
+    vec_append(&sys->conses, &ptr, sizeof(&ptr));
+    break;
+  case TAG_VEC:
+    vec_append(&sys->vectors, &ptr, sizeof(&ptr));
+    break;
+    // Shouldn't be registered
+  case TAG_NIL:
+  case TAG_INT:
+  case TAG_SYM:
+    break;
+  case NUM_TAGS:
+  default:
+    FAIL("Unreachable");
+  }
 }
 
 u64 sys_cost(sys_t *sys)
 {
-  return sym_table_cost(&sys->symtable) + sys->memory.capacity;
+  u64 vec_capacity = 0;
+  for (u64 i = 0; i < VEC_SIZE(&sys->vectors, lisp_t *); ++i)
+  {
+    lisp_t *vec = VEC_GET(&sys->vectors, i, lisp_t *);
+    vec_capacity += as_vec(vec)->capacity;
+  }
+  return sym_table_cost(&sys->symtable) + sys->conses.capacity + vec_capacity;
 }
 
 void sys_free(sys_t *sys)
 {
-  static_assert(NUM_TAGS == 5);
-
   sym_table_free(&sys->symtable);
-  if (sys->memory.size == 0)
-    return;
 
   // Iterate through each cell of memory currently allocated and free them
-  for (size_t i = 0; i < VEC_SIZE(&sys->memory, lisp_t **); ++i)
+  for (size_t i = 0; i < VEC_SIZE(&sys->conses, lisp_t **); ++i)
   {
-    lisp_t *allocated = VEC_GET(&sys->memory, i, lisp_t *);
+    lisp_t *allocated = VEC_GET(&sys->conses, i, lisp_t *);
     lisp_free(allocated);
   }
 
-  // Free the container
-  vec_free(&sys->memory);
+  // Iterate through each cell of memory currently allocated and free them
+  for (size_t i = 0; i < VEC_SIZE(&sys->vectors, lisp_t **); ++i)
+  {
+    lisp_t *allocated = VEC_GET(&sys->vectors, i, lisp_t *);
+    lisp_free(allocated);
+  }
+
+  // Free the containers
+  vec_free(&sys->conses);
+  vec_free(&sys->vectors);
 
   // Ensure no one treats this as active in any sense
   memset(sys, 0, sizeof(*sys));