parser: streamline core list building.

The r_expr grammar symbol is replaced with listacc which has
a different type: a new Yacc node type that has three fields
for building a list from left to right without nreverse,
and the dotted pair item.

* lib.h (struct list_accum): New struct type. Not a great
place for it, but we don't have a parser-specific header that
is included before y.tab.h: parser.h is included after
y.tab.h.

* parser.y (misplaced_consing_dot_check): The val argument
is just the existing dotted item; if it is other than nao,
the error is generated.
(lacc, splacc): New static functions.
(YYSTYPE): New union member, lacc of type struct list_accum.
(r_exprs): Grammar symbol removed.
(listacc): New grammar symbol of type listacc. The rules are
those of r_exprs upgraded to construct the list in one pass.

1 files changed, 6 insertions, 0 deletions

diff --git a/lib.h b/lib.h
index f039568f..708b6724 100644
--- a/lib.h
+++ b/lib.h
@@ -337,6 +337,12 @@ union obj {
   struct dyn_args a;
 };
 
+struct list_accum {
+  obj_t *head;
+  obj_t *tail;
+  obj_t *dot;
+};
+
 #if CONFIG_GEN_GC
 typedef struct {
   val *ptr;