print: print/read consistency problem with rcons.

* lib.c (obj_print_impl): Do not print (rcons X Y)
as X..Y if X looks like (rcons ...). This
causes the problem that (rcons (rcons 1 2) 3)
prints as 1..2..3, a notation which unambiguously
means (rcons 1 (rcons 2 3)).

* tests/012/syntax.tl: New test cases.

2 files changed, 11 insertions, 1 deletions

diff --git a/lib.c b/lib.c
index 0dc756ba..0e374c70 100644
--- a/lib.c
+++ b/lib.c
@@ -14859,7 +14859,8 @@ val obj_print_impl(val obj, val out, val pretty, struct strm_ctx *ctx)
           goto list;
         }
       } else if (sym == rcons_s && have_args
-                 && consp(cdr(args)) && !(cddr(args)))
+                 && consp(cdr(args)) && !(cddr(args)) &&
+                 (!consp(arg) || car(arg) != rcons_s))
       {
         obj_print_impl(arg, out, pretty, ctx);
         put_string(lit(".."), out);
diff --git a/tests/012/syntax.tl b/tests/012/syntax.tl
index d2fab599..bc7d9668 100644
--- a/tests/012/syntax.tl
+++ b/tests/012/syntax.tl
@@ -63,3 +63,12 @@
   '(1.234,e+12) (1.234 (sys:unquote e+12))
   '(1.,234) (1.0 (sys:unquote 234)))
 
+(mtest
+  (read "0..1") (rcons 0 1)
+  (read "0..1..2") (rcons 0 (rcons 1 2)))
+
+(mtest
+  (tostring '(rcons 0 1)) "0..1"
+  (tostring '(rcons 0 (rcons 1 2))) "0..1..2"
+  (tostring '(rcons (rcons 0 1) 2)) "(rcons 0..1 2)"
+  (tostring '(rcons (rcons 0 1) (rcons 2 3))) "(rcons 0..1 2..3)")