--- a/src/ChangeLog	Tue Aug 06 03:42:41 2002 +0000
+++ b/src/ChangeLog	Wed Aug 07 06:54:41 2002 +0000
@@ -1,3 +1,19 @@
+2002-08-07  John W. Eaton  <jwe@bevo.che.wisc.edu>
+
+	* pt-binop.h (tree_binary_expression::is_binary_expression):
+	New function, return true.
+	(tree_boolean_expression::is_boolean_expression): New function,
+	return true.
+	* pt-exp.h (tree_expression::is_binary_expression): New function.
+	(tree_expression::is_boolean_expression): Likewise.
+	* parse.y (EXPR_OR_OR): Now lower precedence than EXPR_AND_AND.
+	(EXPR_OR): Now lower precedence than EXPR_AND.
+	(make_boolean_op): Maybe warn about change in precedence.
+	(make_binary_op): Likewise.
+	(Vwarn_precedence_change): New static variable.
+	(warn_precedence_change): New function.
+	(Vwarn_precedence_change): New DEFVAR.
+
 2002-08-05  John W. Eaton  <jwe@bevo.che.wisc.edu>
 
 	* data.cc (ANY_ALL): Improve arg checks.

--- a/src/parse.y	Tue Aug 06 03:42:41 2002 +0000
+++ b/src/parse.y	Wed Aug 07 06:54:41 2002 +0000
@@ -94,6 +94,11 @@
 // should only produce output using explicit printing statements.
 static bool Vwarn_missing_semicolon;
 
+// If TRUE, generate warning about the meaning of code changing due to
+// changes in precedence levels for various ops (typically for Matlab
+// compatibility).
+static bool Vwarn_precedence_change;
+
 // Temporary symbol table pointer used to cope with bogus function syntax.
 symbol_table *tmp_local_sym_tab = 0;
 
@@ -445,8 +450,10 @@
 // Precedence and associativity.
 %left ';' ',' '\n'
 %right '=' ADD_EQ SUB_EQ MUL_EQ DIV_EQ LEFTDIV_EQ POW_EQ EMUL_EQ EDIV_EQ ELEFTDIV_EQ EPOW_EQ OR_EQ AND_EQ LSHIFT_EQ RSHIFT_EQ
-%left EXPR_AND_AND EXPR_OR_OR
-%left EXPR_AND EXPR_OR
+%left EXPR_OR_OR
+%left EXPR_AND_AND
+%left EXPR_OR
+%left EXPR_AND
 %left EXPR_LT EXPR_LE EXPR_EQ EXPR_NE EXPR_GE EXPR_GT
 %left LSHIFT RSHIFT
 %left ':'
@@ -1963,6 +1970,15 @@
 
     case EXPR_OR:
       t = octave_value::op_el_or;
+      if (Vwarn_precedence_change
+          && op1->paren_count () == 0 && op2->is_binary_expression ())
+        {
+	  tree_binary_expression *e
+	    = dynamic_cast<tree_binary_expression *> (op2);
+
+	  if (e->op_type () == octave_value::op_el_and)
+	    warning ("meaning may have changed due to change in precedence for & and | operators");
+        }
       break;
 
     default:
@@ -1995,6 +2011,15 @@
 
     case EXPR_OR_OR:
       t = tree_boolean_expression::bool_or;
+      if (Vwarn_precedence_change
+          && op1->paren_count () == 0 && op2->is_boolean_expression ())
+        {
+	  tree_boolean_expression *e
+	    = dynamic_cast<tree_boolean_expression *> (op2);
+
+	  if (e->op_type () == tree_boolean_expression::bool_and)
+	    warning ("meaning may have changed due to change in precedence for && and || operators");
+        }
       break;
 
     default:
@@ -3671,6 +3696,14 @@
 }
 
 static int
+warn_precedence_change (void)
+{
+  Vwarn_precedence_change = check_preference ("warn_precedence_change");
+
+  return 0;
+}
+
+static int
 warn_variable_switch_label (void)
 {
   Vwarn_variable_switch_label
@@ -3779,6 +3812,15 @@
 value is 0.\n\
 @end defvr");
 
+  DEFVAR (warn_precedence_change, 1.0, warn_precedence_change,
+    "-*- texinfo -*-\n\
+@defvr {Built-in Variable} warn_precedence_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\
+precedence for some operators.  Precedence changes have typically\n\
+been made for Matlab compatibility.  The default value is 1.\n\
+@end defvr");
+
   DEFVAR (warn_variable_switch_label, 0.0, warn_variable_switch_label,
     "-*- texinfo -*-\n\
 @defvr {Built-in Variable} warn_variable_switch_label\n\

--- a/src/pt-binop.h	Tue Aug 06 03:42:41 2002 +0000
+++ b/src/pt-binop.h	Wed Aug 07 06:54:41 2002 +0000
@@ -62,6 +62,8 @@
       delete op_rhs;
     }
 
+  bool is_binary_expression (void) const { return true; }
+
   bool rvalue_ok (void) const { return true; }
 
   octave_value rvalue (void);
@@ -72,6 +74,8 @@
 
   std::string oper (void) const;
 
+  octave_value::binary_op op_type (void) const { return etype; }
+
   tree_expression *lhs (void) { return op_lhs; }
   tree_expression *rhs (void) { return op_rhs; }
 
@@ -118,6 +122,8 @@
 
   ~tree_boolean_expression (void) { }
 
+  bool is_boolean_expression (void) const { return true; }
+
   bool rvalue_ok (void) const { return true; }
 
   octave_value rvalue (void);
@@ -126,6 +132,8 @@
 
   std::string oper (void) const;
 
+  type op_type (void) const { return etype; }
+
 private:
 
   // The type of the expression.

--- a/src/pt-exp.h	Tue Aug 06 03:42:41 2002 +0000
+++ b/src/pt-exp.h	Wed Aug 07 06:54:41 2002 +0000
@@ -59,6 +59,10 @@
 
   virtual bool is_prefix_expression (void) const { return false; }
 
+  virtual bool is_binary_expression (void) const { return false; }
+
+  virtual bool is_boolean_expression (void) const { return false; }
+
   virtual bool is_logically_true (const char *);
 
   virtual bool lvalue_ok (void) const { return false; }