=== modified file 'pmt/src/lib/pmt.cc'
--- pmt/src/lib/pmt.cc	2009-01-30 14:37:30 +0000
+++ pmt/src/lib/pmt.cc	2009-01-30 14:40:12 +0000
@@ -219,7 +219,7 @@
 }
 
 bool 
-pmt_is_symbol(pmt_t obj)
+pmt_is_symbol(const pmt_t& obj)
 {
   return obj->is_symbol();
 }
@@ -250,7 +250,7 @@
 }
 
 const std::string
-pmt_symbol_to_string(pmt_t sym)
+pmt_symbol_to_string(const pmt_t& sym)
 {
   if (!sym->is_symbol())
     throw pmt_wrong_type("pmt_symbol_to_string", sym);
@@ -364,28 +364,28 @@
 ////////////////////////////////////////////////////////////////////////////
 
 pmt_null::pmt_null() {}
-pmt_pair::pmt_pair(pmt_t car, pmt_t cdr) : d_car(car), d_cdr(cdr) {}
+pmt_pair::pmt_pair(const pmt_t& car, const pmt_t& cdr) : d_car(car), d_cdr(cdr) {}
 
 bool
-pmt_is_null(pmt_t x)
+pmt_is_null(const pmt_t& x)
 {
   return x == PMT_NIL;
 }
 
 bool
-pmt_is_pair(pmt_t obj)
+pmt_is_pair(const pmt_t& obj)
 {
   return obj->is_pair();
 }
 
 pmt_t
-pmt_cons(pmt_t x, pmt_t y)
+pmt_cons(const pmt_t& x, const pmt_t& y)
 {
   return pmt_t(new pmt_pair(x, y));
 }
 
 pmt_t
-pmt_car(pmt_t pair)
+pmt_car(const pmt_t& pair)
 {
   pmt_pair* p = dynamic_cast<pmt_pair*>(pair.get());
   if ( p )
@@ -395,7 +395,7 @@
 }
 
 pmt_t
-pmt_cdr(pmt_t pair)
+pmt_cdr(const pmt_t& pair)
 {
   pmt_pair* p = dynamic_cast<pmt_pair*>(pair.get());
   if ( p )
@@ -681,13 +681,13 @@
 ////////////////////////////////////////////////////////////////////////////
 
 bool
-pmt_eq(pmt_t x, pmt_t y)
+pmt_eq(const pmt_t& x, const pmt_t& y)
 {
   return x == y;
 }
 
 bool
-pmt_eqv(pmt_t x, pmt_t y)
+pmt_eqv(const pmt_t& x, const pmt_t& y)
 {
   if (x == y)
     return true;
@@ -705,7 +705,7 @@
 }
 
 bool
-pmt_equal(pmt_t x, pmt_t y)
+pmt_equal(const pmt_t& x, const pmt_t& y)
 {
   if (pmt_eqv(x, y))
     return true;
@@ -747,7 +747,7 @@
 }
 
 size_t
-pmt_length(pmt_t x)
+pmt_length(const pmt_t& x)
 {
   if (x->is_vector())
     return _vector(x)->length();
@@ -755,13 +755,16 @@
   if (x->is_uniform_vector())
     return _uniform_vector(x)->length();
 
-  if (x->is_pair() || x->is_null()) {
-    size_t length=0;
-    while (pmt_is_pair(x)){
+  if (x->is_null()) return 0;
+
+  if (x->is_pair()) {
+    size_t length=1;
+	pmt_t it = pmt_cdr(x);
+    while (pmt_is_pair(it)){
       length++;
-      x = pmt_cdr(x);
+      it = pmt_cdr(it);
     }
-    if (pmt_is_null(x))
+    if (pmt_is_null(it))
       return length;
 
     // not a proper list
@@ -822,7 +825,7 @@
 }
 
 pmt_t
-pmt_map(pmt_t proc(pmt_t), pmt_t list)
+pmt_map(pmt_t proc(const pmt_t&), pmt_t list)
 {
   pmt_t r = PMT_NIL;
 

=== modified file 'pmt/src/lib/pmt.h'
--- pmt/src/lib/pmt.h	2008-06-26 17:17:15 +0000
+++ pmt/src/lib/pmt.h	2009-01-30 14:40:12 +0000
@@ -109,7 +109,7 @@
  */
 
 //! Return true if obj is a symbol, else false.
-bool pmt_is_symbol(pmt_t obj);
+bool pmt_is_symbol(const pmt_t& obj);
 
 //! Return the symbol whose name is \p s.
 pmt_t pmt_string_to_symbol(const std::string &s);
@@ -122,7 +122,7 @@
  * If \p is a symbol, return the name of the symbol as a string.
  * Otherwise, raise the wrong_type exception.
  */
-const std::string pmt_symbol_to_string(pmt_t sym);
+const std::string pmt_symbol_to_string(const pmt_t& sym);
 
 /*
  * ------------------------------------------------------------------------
@@ -206,19 +206,19 @@
 extern const pmt_t PMT_NIL;	//< the empty list
 
 //! Return true if \p x is the empty list, otherwise return false.
-bool pmt_is_null(pmt_t x);
+bool pmt_is_null(const pmt_t& x);
 
 //! Return true if \p obj is a pair, else false.
-bool pmt_is_pair(pmt_t obj);
+bool pmt_is_pair(const pmt_t& obj);
 
 //! Return a newly allocated pair whose car is \p x and whose cdr is \p y.
-pmt_t pmt_cons(pmt_t x, pmt_t y);
+pmt_t pmt_cons(const pmt_t& x, const pmt_t& y);
 
 //! If \p pair is a pair, return the car of the \p pair, otherwise raise wrong_type.
-pmt_t pmt_car(pmt_t pair);
+pmt_t pmt_car(const pmt_t& pair);
 
 //! If \p pair is a pair, return the cdr of the \p pair, otherwise raise wrong_type.
-pmt_t pmt_cdr(pmt_t pair);
+pmt_t pmt_cdr(const pmt_t& pair);
 
 //! Stores \p value in the car field of \p pair.
 void pmt_set_car(pmt_t pair, pmt_t value);
@@ -449,7 +449,7 @@
  */
 
 //! Return true if x and y are the same object; otherwise return false.
-bool pmt_eq(pmt_t x, pmt_t y);
+bool pmt_eq(const pmt_t& x, const pmt_t& y);
 
 /*!
  * \brief Return true if x and y should normally be regarded as the same object, else false.
@@ -464,7 +464,7 @@
  *   x and y are pairs or vectors that denote same location in store.
  * </pre>
  */
-bool pmt_eqv(pmt_t x, pmt_t y);
+bool pmt_eqv(const pmt_t& x, const pmt_t& y);
 
 /*!
  * pmt_equal recursively compares the contents of pairs and vectors,
@@ -472,11 +472,11 @@
  * pmt_equal may fail to terminate if its arguments are circular data
  * structures.
  */
-bool pmt_equal(pmt_t x, pmt_t y);
+bool pmt_equal(const pmt_t& x, const pmt_t& y);
 
 
 //! Return the number of elements in v
-size_t pmt_length(pmt_t v);
+size_t pmt_length(const pmt_t& v);
 
 /*!
  * \brief Find the first pair in \p alist whose car field is \p obj
@@ -515,7 +515,7 @@
  * \p list must be a list.  The dynamic order in which \p proc is
  * applied to the elements of \p list is unspecified.
  */
-pmt_t pmt_map(pmt_t proc(pmt_t), pmt_t list);
+pmt_t pmt_map(pmt_t proc(const pmt_t&), pmt_t list);
 
 /*!
  * \brief reverse \p list.

=== modified file 'pmt/src/lib/pmt_int.h'
--- pmt/src/lib/pmt_int.h	2008-06-26 17:17:15 +0000
+++ pmt/src/lib/pmt_int.h	2009-01-30 14:40:12 +0000
@@ -151,7 +151,7 @@
   pmt_t		d_cdr;
 
 public:
-  pmt_pair(pmt_t car, pmt_t cdr);
+  pmt_pair(const pmt_t& car, const pmt_t& cdr);
   //~pmt_pair(){};
 
   bool is_pair() const { return true; }