parser: @(mdo) must not be subject to expand-meta.

* parser.y (elem): When the elem is a list, if it starts with mdo, then
we evaluate it immediately and substitute (do) as the semantic
value.  We no longer not allow mdo to precipitate into
match_expand_elem, where expand_meta will be unleashed on it.
Doing so causes the bug that expessions like @1, denoting
the form (sys:var 1), are rewritten to (sys:expr 1), which op
syntax. So two bugs are fixed: the incorrect treatment of
meta-syntax, and the neglect to perform mdo in nested
contexts.
(check_parse_time_action): We need not handle mdo here any
more; it will never make it into this function.
Only actions done in the main clause list belong here,
not parse time actions done at any nesting level.

* tests/008/mdo.txr: New file.

* y.tab.c.shipped: Updated.

1 files changed, 3 insertions, 4 deletions

diff --git a/parser.y b/parser.y
index 7e068714..8d5e3035 100644
--- a/parser.y
+++ b/parser.y
@@ -498,6 +498,9 @@ elem : texts                    { $$ = rlc(cons(text_s, $1), $1);
                                     $$ = rlc(cons(sym,
                                                    expand_forms(rest($1), nil)),
                                               $1);
+                                  else if (sym == mdo_s)
+                                  { eval_intrinsic(cons(progn_s, cdr($1)), nil);
+                                    $$ = cons(do_s, nil); }
                                   else
                                   { $$ = match_expand_elem($1);
                                     match_reg_elem($$); } }
@@ -2016,10 +2019,6 @@ static val check_parse_time_action(val spec_rev)
       if (sym == include_s) {
         return nappend2(nreverse(include(line)), rest(spec_rev));
       }
-      if (sym == mdo_s) {
-        eval_intrinsic(cons(progn_s, cdr(elem)), nil);
-        return nil;
-      }
       if (sym == in_package_s) {
         eval_intrinsic(elem, nil);
         return nil;