diff --git a/pila.c b/pila.c
index 85c6c1b..634b174 100644
--- a/pila.c
+++ b/pila.c
@@ -57,15 +57,18 @@ struct Word {
 
 struct RpnState {
 	Value data_stack[DATA_STACK_LEN];
-	Word *rts[RETURN_STACK_LEN];
-
+	Word *rts[RETURN_STACK_LEN]; /* "return" stack */
+	/* stack, return pointers */
 	isize sp, rp;
-	bool err;
+	/* linked list, last added word is the first */
 	DictionaryEntry *dict;
 	
-	bool compiling;
+	/* state flags XXX: use a bitfield? */
+	bool err, compiling;
+	/* reader pointers */
 	char *rsp; /* reader start pointer */
 	char *rep; /* "      end   " */
+	/* current word compilation state */
 	UserWord cur_comp;
 	isize cur_comp_cap;
 	Str cur_comp_name;