--- a/src/ChangeLog	Wed Feb 23 01:43:50 2005 +0000
+++ b/src/ChangeLog	Wed Feb 23 16:44:59 2005 +0000
@@ -1,3 +1,13 @@
+2005-02-23  John W. Eaton  <jwe@octave.org>
+
+	* parse.y (fold (tree_binary_expression*)): Skip constant folding
+	for some expressions to preserve warnings.
+	(Vwarn_associativity_change): New static variable.
+	(warn_associativity_change): New function.
+	(symbols_of_parse): DEFVAR warn_associativity_change.
+	(maybe_warn_associativity_change): New function.
+	(make_binary_op): Use it.
+
 2005-02-22  John W. Eaton  <jwe@octave.org>
 
 	* parse.y (POW, EPOW): Use %left associativity for compatibility.

--- a/src/parse.y	Wed Feb 23 01:43:50 2005 +0000
+++ b/src/parse.y	Wed Feb 23 16:44:59 2005 +0000
@@ -80,8 +80,10 @@
 //
 static bool Vwarn_assign_as_truth_value;
 
-// If TRUE, generate a warning for variable swich labels.
-static bool Vwarn_variable_switch_label;
+// If TRUE, generate warning about the meaning of code changing due to
+// changes in associativity for various ops (typically for Matlab
+// compatibility).
+static bool Vwarn_associativity_change;
 
 // If TRUE, generate warning if declared function name disagrees with
 // the name of the file in which it is defined.
@@ -100,6 +102,9 @@
 // compatibility).
 static bool Vwarn_precedence_change;
 
+// If TRUE, generate a warning for variable switch labels.
+static bool Vwarn_variable_switch_label;
+
 // Temporary symbol table pointer used to cope with bogus function syntax.
 symbol_table *tmp_local_sym_tab = 0;
 
@@ -1580,7 +1585,13 @@
   tree_expression *op1 = e->lhs ();
   tree_expression *op2 = e->rhs ();
 
-  if (op1->is_constant () && op2->is_constant ())
+  octave_value::binary_op op_type = e->op_type ();
+
+  if (op1->is_constant () && op2->is_constant ()
+      && (! ((Vwarn_associativity_change
+	      && (op_type == POW || op_type == EPOW))
+	     || (Vwarn_precedence_change
+		 && (op_type == EXPR_OR || op_type == EXPR_OR_OR)))))
     {
       octave_value tmp = e->rvalue ();
 
@@ -1840,6 +1851,27 @@
   return retval;
 }
 
+static void
+maybe_warn_associativity_change (tree_expression *op)
+{
+  if (Vwarn_associativity_change
+      && op->paren_count () == 0 && op->is_binary_expression ())
+    {
+      tree_binary_expression *e
+	= dynamic_cast<tree_binary_expression *> (op);
+
+      octave_value::binary_op op_type = e->op_type ();
+
+      if (op_type == octave_value::op_pow
+	  || op_type == octave_value::op_el_pow)
+	{
+	  std::string op_str = octave_value::binary_op_as_string (op_type);
+
+	  warning ("meaning may have changed due to change in associativity for %s operator", op_str.c_str ());
+        }
+    }
+}
+
 // Build a binary expression.
 
 static tree_expression *
@@ -1852,10 +1884,12 @@
     {
     case POW:
       t = octave_value::op_pow;
+      maybe_warn_associativity_change (op1);
       break;
 
     case EPOW:
       t = octave_value::op_el_pow;
+      maybe_warn_associativity_change (op1);
       break;
 
     case '+':
@@ -3848,6 +3882,14 @@
 }
 
 static int
+warn_associativity_change (void)
+{
+  Vwarn_associativity_change = check_preference ("warn_associativity_change");
+
+  return 0;
+}
+
+static int
 warn_function_name_clash (void)
 {
   Vwarn_function_name_clash = check_preference ("warn_function_name_clash");
@@ -3955,6 +3997,15 @@
 The default value of @code{warn_assign_as_truth_value} is 1.\n\
 @end defvr");
 
+  DEFVAR (warn_associativity_change, true, warn_associativity_change,
+    "-*- texinfo -*-\n\
+@defvr {Built-in Variable} warn_associativity_change\n\
+If the value of this variable is nonzero, Octave will warn about\n\
+possible changes in the meaning of some code due to changes in\n\
+associativity for some operators.  Associativity changes have typically\n\
+been made for Matlab compatibility.  The default value is 1.\n\
+@end defvr");
+
   DEFVAR (warn_function_name_clash, true, warn_function_name_clash,
     "-*- texinfo -*-\n\
 @defvr {Built-in Variable} warn_function_name_clash\n\