doc: note about circular notation and hashes.

* txr.1: Document that circular notation works with
eql-based hash tables, but not equal-based.

1 files changed, 13 insertions, 0 deletions

diff --git a/txr.1 b/txr.1
index 3c5dbc74..db749592 100644
--- a/txr.1
+++ b/txr.1
@@ -10919,6 +10919,19 @@ or lexically precedes the reference.  Forward references such as
 .code "(#1# #1=(1 2))"
 are not supported.
 
+.TP* "Note:"
+Circular notation can span hash table literals. The syntax
+.code "#1=#H(() (#1# #1#))"
+denotes an
+.codn eql -based
+hash table which contains one entry, in which that
+same table itself is both the key and value. This kind of
+circularity is not supported for
+.codn equal -based
+hash tables. The analogous syntax
+.code "#1=#H((:equal-based) (#1# #1#))"
+produces a hash table in an inconsistent state.
+
 .TP* "Dialect note:"
 Circle notation is taken from Common Lisp, 
 intended to be unsurprising to users familiar with that