add depth and unused

src/fh_builtins.c

@@ -985,7 +985,15 @@ static enum fh_error w_depth(struct fh_thread_s *fh, const struct fh_word_s *w)
 {
   (void) w;
   enum fh_error rv;
-  TRY(ds_push(fh, w->param));
+  TRY(ds_push(fh, fh->data_stack_top));
+  return FH_OK;
+}
+
+static enum fh_error w_unused(struct fh_thread_s *fh, const struct fh_word_s *w)
+{
+  (void) w;
+  enum fh_error rv;
+  TRY(ds_push(fh, HEAP_SIZE - fh->heap_top));
   return FH_OK;
 }
 
@@ -1123,6 +1131,8 @@ enum fh_error register_builtin_words(struct fh_thread_s *fh)
       {"aligned",   w_aligned,         0, 0},
       {"allot",     w_allot,           0, 0},
       {"align",     w_align,           0, 0},
+      {"depth",     w_depth,           0, 0},
+      {"unused",    w_unused,          0, 0},
       {",",         w_comma,           0, 0},
       // TODO +!
       // TODO pictured numbers (#)