From b76485e540762c60ba34dc36875c3b936f4df7b8 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Sun, 16 Feb 2014 16:26:31 -0800
Subject: * eval.c (op_tree_case): Removed superfluous handling of nil
 parameter list; this is correctly handled by bind_macro_params. Added support
 for the colon symbol as an indication that the case is declined.

* txr.1: Updated.
---
 ChangeLog |  9 +++++++++
 eval.c    | 13 +++++--------
 txr.1     | 11 ++++++++---
 3 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 83be43f8..3ba822c1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2014-02-16  Kaz Kylheku  <kaz@kylheku.com>
+
+	* eval.c (op_tree_case): Removed superfluous handling of
+	nil parameter list; this is correctly handled by bind_macro_params.
+	Added support for the colon symbol as an indication that
+	the case is declined.
+
+	* txr.1: Updated.
+
 2014-02-16  Kaz Kylheku  <kaz@kylheku.com>
 
 	New destructuring operators.
diff --git a/eval.c b/eval.c
index e7ad031d..54e7024e 100644
--- a/eval.c
+++ b/eval.c
@@ -1107,15 +1107,12 @@ static val op_tree_case(val form, val env)
   for (; consp(cases); cases = cdr(cases)) {
     val onecase = car(cases);
     cons_bind (params, forms, onecase);
-
-    if (!params) {
-      if (!expr_val)
-        return eval_progn(forms, env, forms);
-    } else {
-      val new_env = bind_macro_params(env, nil, params, expr_val,
+    val new_env = bind_macro_params(env, nil, params, expr_val,
                                       colon_k, onecase);
-      if (new_env)
-        return eval_progn(forms, new_env, forms);
+    if (new_env) {
+      val ret = eval_progn(forms, new_env, forms);
+      if (ret != colon_k)
+        return ret;
     }
   }
 
diff --git a/txr.1 b/txr.1
index d47af3a8..2ccb8338 100644
--- a/txr.1
+++ b/txr.1
@@ -12689,9 +12689,14 @@ style parameter list <macro-style-params>.
 
 If the object produced by <expr> matches <macro-style-params>, then the
 parameters are bound, becoming local variables, and the <form>-s, if any, are
-evaluated in order in the environment in which those variables are visible. The
-evaluation of tree-case then ends, returning the value of the last <form>, or
-else nil if there are no forms.
+evaluated in order in the environment in which those variables are visible. 
+
+If there are forms, the value of the last <form> becomes the result value of
+the case, otherwise the result value of the case is nil.
+
+If the result value of a case is the object : (the colon symbol), then
+processing continues with the next case. Otherwise the evaluation of tree-case
+terminates, returning the result value.
 
 If the value of <expr> does not match the <macro-style-params> parameter
 list, then the usual exception is thrown; instead, processing continues
-- 
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