Fix pretty printer mishandling unexpected syntax.

* lib.c (obj_print_impl): When rendering quote,
quasiquote, unquote, splice, vector literals, and
meta-vars/meta-numbers into their read syntax, we must ensure
that these forms have the correct abstract syntax. If not, we
must print these as ordinary compound expressions. Otherwise
we throw errors, or don't print the complete object.

1 files changed, 8 insertions, 7 deletions

diff --git a/lib.c b/lib.c
index bddf7f4a..745714f9 100644
--- a/lib.c
+++ b/lib.c
@@ -7820,27 +7820,28 @@ val obj_print_impl(val obj, val out, val pretty)
       val save_mode = test_set_indent_mode(out, num_fast(indent_off),
                                            num_fast(indent_data));
       val save_indent = nil;
+      int two_elem = consp(cdr(obj)) && !cddr(obj);
 
-      if (sym == quote_s && consp(cdr(obj)) && !(cdr(cdr(obj)))) {
+      if (sym == quote_s && two_elem) {
         put_char(chr('\''), out);
         obj_print_impl(second(obj), out, pretty);
-      } else if (sym == sys_qquote_s) {
+      } else if (sym == sys_qquote_s && two_elem) {
         put_char(chr('^'), out);
         obj_print_impl(second(obj), out, pretty);
-      } else if (sym == sys_unquote_s) {
+      } else if (sym == sys_unquote_s && two_elem) {
         put_char(chr(','), out);
         obj_print_impl(second(obj), out, pretty);
-      } else if (sym == sys_splice_s) {
+      } else if (sym == sys_splice_s && two_elem) {
         put_string(lit(",*"), out);
         obj_print_impl(second(obj), out, pretty);
-      } else if (sym == vector_lit_s) {
+      } else if (sym == vector_lit_s && two_elem) {
         put_string(lit("#"), out);
         obj_print_impl(second(obj), out, pretty);
       } else if (sym == hash_lit_s) {
         put_string(lit("#H"), out);
         obj_print_impl(rest(obj), out, pretty);
-      } else if (sym == var_s && (symbolp(second(obj)) || integerp(second(obj)))
-                 && !cdr(cdr(obj)))
+      } else if (sym == var_s && two_elem &&
+                 (symbolp(second(obj)) || integerp(second(obj))))
       {
         put_char(chr('@'), out);
         obj_print_impl(second(obj), out, pretty);