--- a/src/pr-output.cc
+++ b/src/pr-output.cc
@@ -139,7 +139,7 @@
 }
 
 static double
-pr_max_internal (Matrix& m)
+pr_max_internal (const Matrix& m)
 {
   int nr = m.rows ();
   int nc = m.columns ();
@@ -160,7 +160,7 @@
 }
 
 static double
-pr_min_internal (Matrix& m)
+pr_min_internal (const Matrix& m)
 {
   int nr = m.rows ();
   int nc = m.columns ();
@@ -272,7 +272,7 @@
 }
 
 static void
-set_format (Matrix& m, int& fw)
+set_format (const Matrix& m, int& fw)
 {
   curr_real_fmt = (char *) NULL;
   curr_imag_fmt = (char *) NULL;
@@ -379,14 +379,14 @@
 }
 
 static inline void
-set_format (Matrix& m)
+set_format (const Matrix& m)
 {
   int fw;
   set_format (m, fw);
 }
 
 static void
-set_format (Complex& c, int& r_fw, int& i_fw)
+set_format (const Complex& c, int& r_fw, int& i_fw)
 {
   curr_real_fmt = (char *) NULL;
   curr_imag_fmt = (char *) NULL;
@@ -518,14 +518,14 @@
 }
 
 static inline void
-set_format (Complex& c)
+set_format (const Complex& c)
 {
   int r_fw, i_fw;
   set_format (c, r_fw, i_fw);
 }
 
 static void
-set_format (ComplexMatrix& cm, int& r_fw, int& i_fw)
+set_format (const ComplexMatrix& cm, int& r_fw, int& i_fw)
 {
   curr_real_fmt = (char *) NULL;
   curr_imag_fmt = (char *) NULL;
@@ -656,7 +656,7 @@
 }
 
 static int
-all_elements_are_ints (Range& r)
+all_elements_are_ints (const Range& r)
 {
 // If the base and increment are ints, the final value in the range
 // will also be an integer, even if the limit is not.
@@ -668,14 +668,14 @@
 }
 
 static inline void
-set_format (ComplexMatrix& cm)
+set_format (const ComplexMatrix& cm)
 {
   int r_fw, i_fw;
   set_format (cm, r_fw, i_fw);
 }
 
 static void
-set_format (Range& r, int& fw)
+set_format (const Range& r, int& fw)
 {
   curr_real_fmt = (char *) NULL;
   curr_imag_fmt = (char *) NULL;
@@ -777,14 +777,14 @@
 }
 
 static inline void
-set_format (Range& r)
+set_format (const Range& r)
 {
   int fw;
   set_format (r, fw);
 }
 
 static inline void
-pr_any_float (char *fmt, ostrstream& os, double d, int fw = 0)
+pr_any_float (const char *fmt, ostrstream& os, double d, int fw = 0)
 {
   if (d == -0.0)
     d = 0.0;
@@ -831,7 +831,7 @@
 }
 
 static inline void
-pr_complex (ostrstream& os, Complex& c, int r_fw = 0, int i_fw = 0)
+pr_complex (ostrstream& os, const Complex& c, int r_fw = 0, int i_fw = 0)
 {
   double r = c.real ();
   pr_float (os, r, r_fw);
@@ -875,7 +875,7 @@
 }
 
 void
-octave_print_internal (ostrstream& os, Matrix& m)
+octave_print_internal (ostrstream& os, const Matrix& m)
 {
   int nr = m.rows ();
   int nc = m.columns ();
@@ -953,7 +953,7 @@
 }
 
 void
-octave_print_internal (ostrstream& os, Complex& c)
+octave_print_internal (ostrstream& os, const Complex& c)
 {
   if (plus_format)
     {
@@ -974,7 +974,7 @@
 }
 
 void
-octave_print_internal (ostrstream& os, ComplexMatrix& cm)
+octave_print_internal (ostrstream& os, const ComplexMatrix& cm)
 {
   int nr = cm.rows ();
   int nc = cm.columns ();
@@ -1056,7 +1056,7 @@
 }
 
 void
-octave_print_internal (ostrstream& os, Range& r)
+octave_print_internal (ostrstream& os, const Range& r)
 {
   double b = r.base ();
   double increment = r.inc ();