printer: do not render @(rcons ...) in .. notation.

This fixes the following print-read consistency issue.
Both of these objects print as @a..@b.

  1> '@(rcons a b)
  @a..b
  2> '(rcons @a b)
  @a..b

We want only the second case. After the this fix:

  1> '(rcons @a b)
  @a..b
  2> '@(rcons a b)
  @(rcons a b)

* lib.c (obj_print_impl): In the sys:expr case, we check
whether the head of the argument is rcons.  If so, we adjust a
few local variables and branch directly to the generic list
case via goto to print the argument as (rcons ...) without
conversion to dotdot range notation.

1 files changed, 11 insertions, 2 deletions

diff --git a/lib.c b/lib.c
index f31b8e79..4fdcaacf 100644
--- a/lib.c
+++ b/lib.c
@@ -12383,8 +12383,17 @@ val obj_print_impl(val obj, val out, val pretty, struct strm_ctx *ctx)
         put_char(chr('@'), out);
         obj_print_impl(arg, out, pretty, ctx);
       } else if (sym == expr_s && two_elem && consp(arg)) {
+        val inarg = car(arg);
         put_char(chr('@'), out);
-        obj_print_impl(arg, out, pretty, ctx);
+        if (inarg != rcons_s) {
+          obj_print_impl(arg, out, pretty, ctx);
+        } else {
+          obj = arg;
+          sym = inarg;
+          args = cdr(obj);
+          arg = car(obj);
+          goto list;
+        }
       } else if (sym == rcons_s && have_args
                  && consp(cdr(args)) && !(cddr(args)))
       {
@@ -12440,7 +12449,7 @@ val obj_print_impl(val obj, val out, val pretty, struct strm_ctx *ctx)
           args = cdr(args);
         }
         put_char(chr('`'), out);
-      } else {
+      } else list: {
         val iter;
         val closepar = chr(')');
         val indent = zero;