printer: [] shouldn't print as [. nil].

* lib.c (obj_print_impl): In the case when dwim
has no args, and the logic short circuits to
a closing brace, bypassing the loop, we should
only use the dot notation if the terminating
atom is other than nil.

* tests/012/readprint.tl: Tests added.

2 files changed, 11 insertions, 3 deletions

diff --git a/lib.c b/lib.c
index f9b6ee30..d17e416f 100644
--- a/lib.c
+++ b/lib.c
@@ -14349,8 +14349,10 @@ val obj_print_impl(val obj, val out, val pretty, struct strm_ctx *ctx)
         if (sym == dwim_s) {
           put_char(chr('['), out);
           if (!have_args) {
-            put_string(lit(". "), out);
-            obj_print_impl(args, out, pretty, ctx);
+            if (args) {
+              put_string(lit(". "), out);
+              obj_print_impl(args, out, pretty, ctx);
+            }
             put_char(chr(']'), out);
             break;
           }
diff --git a/tests/012/readprint.tl b/tests/012/readprint.tl
index cf70320a..4298a85b 100644
--- a/tests/012/readprint.tl
+++ b/tests/012/readprint.tl
@@ -4,4 +4,10 @@
   '[ . a] "[. a]"
   '[. a] "[. a]"
   '[ . @a] "[. @a]"
-  '[. @a] "[. @a]")
+  '[. @a] "[. @a]"
+  '[] "[]"
+  '[. 3] "[. 3]"
+  '[3 . 4] "[3 . 4]"
+  '(dwim) "[]"
+  '(dwim . 3) "[. 3]"
+  '(dwim 3 . 4) "[3 . 4]")