bugfix: quasilit read/print consistency, part 1.

The bug is that `@@@a` prints as `@@a` which
reads as a different object.

In this patch we simplify how quasiliterals are represented.
Embedded expressions are no longer (sys:expr E), just E.
Meta-numbers N and variables V are still (sys:var N).

However `@@a` and `@a` remain equivalent.

* eval.c (subst_vars): No need to look for expr_s;
just evaluate a compound form. The recursive nested
case is unnecessary and is removed.
(expand_quasi): Do nothandle expr_s; it is not
part of the quasi syntax any more.

* lib.c (out_quasi_str): Do not look for expr_s in the
quasi syntax; just print any expression with a @
the fallback case.

* match.c (tx_subst_vars): Analogous changes to those
done in subst_vars in eval.c.

* parser.y (quasi_meta_helper): Static function removed.
This was responsible for the issue due to stripping a
level of meta from expressions already having a meta
on them.
(quasi_item): In the `@` n_expr syntax case, no longer
call quasi_meta_helper. The remaining logic is simple
enough to put in line. Symbols and integers get wrapped
with (sys:var ...); other expressions are integrated
into the syntax as-is.

1 files changed, 5 insertions, 20 deletions

diff --git a/parser.y b/parser.y
index 8d3e5a89..b54c7bf8 100644
--- a/parser.y
+++ b/parser.y
@@ -68,7 +68,6 @@ static val rlrec(parser_t *, val form, val line);
 static wchar_t char_from_name(const wchar_t *name);
 static val make_expr(parser_t *, val sym, val rest, val lineno);
 static val check_for_include(val spec_rev);
-static val quasi_meta_helper(val obj);
 static void misplaced_consing_dot_check(scanner_t *scanner, val term_atom_cons);
 
 #if YYBISON
@@ -1165,7 +1164,11 @@ quasi_item : litchars           { $$ = lit_char_helper($1); }
            | q_var              { $$ = $1; }
            | METANUM            { $$ = cons(var_s, cons($1, nil));
                                   rl($$, num(parser->lineno)); }
-           | '@' n_expr         { $$ = quasi_meta_helper($2); }
+           | '@' n_expr         { if (integerp($2) || symbolp($2))
+                                    $$ = rlcp_tree(cons(var_s, cons($2, nil)),
+                                                   $2);
+                                  else
+                                    $$ = $2; }
            ;
 
 litchars : LITCHAR              { $$ = rl(cons(chr($1), nil), num(parser->lineno)); }
@@ -1644,24 +1647,6 @@ static val check_for_include(val spec_rev)
   return spec_rev;
 }
 
-static val quasi_meta_helper(val obj)
-{
-  if (integerp(obj) || symbolp(obj))
-    goto var;
-
-  if (atom(obj))
-    goto expr;
-
-  if (first(obj) == var_s || first(obj) == expr_s)
-    return obj;
-
-expr:
-  return rlcp(cons(expr_s, obj), obj);
-
-var:
-  return rlcp_tree(cons(var_s, cons(obj, nil)), obj);
-}
-
 static void misplaced_consing_dot_check(scanner_t *scanner, val term_atom_cons)
 {
   if (car(term_atom_cons) != unique_s) {