diff --git a/guile-readline/ChangeLog b/guile-readline/ChangeLog
index d010037cd..b8f3410fe 100644
--- a/guile-readline/ChangeLog
+++ b/guile-readline/ChangeLog
@@ -1,3 +1,8 @@
+2001-06-07  Dirk Herrmann  <D.Herrmann@tu-bs.de>
+
+	* readline.c (current_input_getc):  Mark unused parameters with
+	SCM_UNUSED.
+
 2001-06-03  Marius Vollmer  <mvo@zagadka.ping.de>
 
 	* configure.in: Added AC_PREREQ(2.50) and minimally changed for
diff --git a/guile-readline/readline.c b/guile-readline/readline.c
index 6070e174f..b085f94d8 100644
--- a/guile-readline/readline.c
+++ b/guile-readline/readline.c
@@ -1,6 +1,6 @@
 /* readline.c --- line editing support for Guile */
 
-/*	Copyright (C) 1997,1999, 2000 Free Software Foundation, Inc.
+/* Copyright (C) 1997,1999,2000,2001 Free Software Foundation, Inc.
  * 
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -128,7 +128,7 @@ static SCM input_port;
 static SCM before_read;
 
 static int
-current_input_getc (FILE *in)
+current_input_getc (FILE *in SCM_UNUSED)
 {
   if (promptp && !SCM_FALSEP (before_read))
     {
diff --git a/libguile/ChangeLog b/libguile/ChangeLog
index a4cc49e64..ef708e74e 100644
--- a/libguile/ChangeLog
+++ b/libguile/ChangeLog
@@ -1,3 +1,77 @@
+2001-06-07  Dirk Herrmann  <D.Herrmann@tu-bs.de>
+
+	* __scm.h (SCM_NORETURN):  Moved here from error.h.
+
+	(SCM_UNUSED):  New macro.
+
+	(SCM_DEBUG_PAIR_ACCESSES):  New macro.
+
+	* backtrace.c (display_error_handler), continuations.c
+	(continuation_print), debug.c (debugobj_print), dynwind.c
+	(guards_print), environments.c (observer_print,
+	core_environments_finalize, leaf_environment_cell,
+	leaf_environment_print, eval_environment_print,
+	eval_environment_observer, import_environment_define,
+	import_environment_undefine, import_environment_print,
+	import_environment_observer, export_environment_define,
+	export_environment_undefine, export_environment_print,
+	export_environment_observer), eval.c (scm_m_quote, scm_m_begin,
+	scm_m_if, scm_m_set_x, scm_m_and, scm_m_or, scm_m_case,
+	scm_m_cond, scm_m_lambda, scm_m_letstar, scm_m_do, scm_m_delay,
+	scm_m_letrec1, scm_m_apply, scm_m_cont, scm_m_nil_cond,
+	scm_m_nil_ify, scm_m_t_ify, scm_m_0_cond, scm_m_0_ify,
+	scm_m_1_ify, scm_m_atfop, scm_m_at_call_with_values), evalext.c
+	(scm_m_generalized_set_x), fluids.c (fluid_print), fports.c
+	(fport_print), gc.c (gc_start_stats, scm_remember_upto_here_1,
+	scm_remember_upto_here_2, scm_remember_upto_here, mark_gc_async),
+	gh_init.c (gh_standard_handler), goops.c (get_slot_value,
+	set_slot_value, test_slot_existence, scm_change_object_class,
+	scm_m_atslot_ref, scm_m_atslot_set_x, make_struct_class,
+	default_setter), guardians.c (guardian_print, guardian_gc_init,
+	guardian_zombify, whine_about_self_centered_zombies), guile.c
+	(inner_main), init.c (stream_handler), keywords.c (keyword_print),
+	mallocs.c (malloc_print), numbers.c (scm_print_real,
+	scm_print_complex, scm_bigprint), ports.c (flush_port_default,
+	end_input_default, scm_port_print, fill_input_void_port,
+	write_void_port), root.c (root_print), smob.c (scm_mark0,
+	scm_free0, scm_smob_print, scm_smob_apply_1_error,
+	scm_smob_apply_2_error, scm_smob_apply_3_error, free_print),
+	stime.c (restorezone), strings.c (scm_makfromstr), struct.c
+	(scm_struct_free_0, scm_struct_free_standard,
+	scm_struct_free_entity, scm_struct_gc_init, scm_free_structs),
+	throw.c (jmpbuffer_print, lazy_catch_print, ss_handler,
+	scm_handle_by_throw, scm_ithrow), weaks.c
+	(scm_weak_vector_gc_init, scm_mark_weak_vector_spines,
+	scm_scan_weak_vectors), ramap.c (scm_array_fill_int), filesys.c
+	(scm_dir_print): Mark unused parameters with SCM_UNUSED.
+
+	* error.h (SCM_NORETURN):  Moved to __scm.h.
+
+	* error.h (ERRORH, SCM_ERROR_H), pairs.h (PAIRSH, SCM_PAIRS_H):
+	Renamed <foo>H to SCM_<foo>_H.
+
+	* gc.c (debug_cells_gc_interval):  New static variable.
+
+	(scm_assert_cell_valid):  If selected by the user, perform
+	additional garbage collections.
+
+	(scm_set_debug_cell_accesses_x):  Extended to let the user specify
+	if additional garbage collections are desired.
+
+	(mark_gc_async):  If additional garbage collections are selected
+	by the user, don't call the after-gc-hook.  Instead require the
+	user to run the hook manually.
+
+	* pairs.c (scm_error_pair_access):  New function.  Only compiled
+	if SCM_DEBUG_PAIR_ACCESSES is set to 1.
+
+	* pairs.h (SCM_VALIDATE_PAIR):  New macro.
+
+	(SCM_CAR, SCM_CDR, SCM_SETCAR, SCM_SETCDR):  If
+	SCM_DEBUG_PAIR_ACCESSES is set to 1, make sure that the argument
+	is a real pair object.  (Glocs are also accepted, but that may
+	change.)  If not, abort with an error message.
+
 2001-06-05  Dirk Herrmann  <D.Herrmann@tu-bs.de>
 
 	* eval.c (SCM_VALIDATE_NON_EMPTY_COMBINATION):  New macro.
diff --git a/libguile/__scm.h b/libguile/__scm.h
index 2a06b9caa..f5e7ed3a0 100644
--- a/libguile/__scm.h
+++ b/libguile/__scm.h
@@ -55,6 +55,38 @@
    should go in __scm.h.  */
 
 
+/* {Compiler hints}
+ *
+ * The following macros are used to provide additional information for the
+ * compiler, which may help to do better error checking and code
+ * optimization.  A second benefit of these macros is, that they also provide
+ * additional information to the developers.
+ */
+
+/* The macro SCM_NORETURN indicates that a function will never return.
+ * Examples:
+ *   1) int foo (char arg) SCM_NORETURN;
+ */
+#ifdef __GNUC__
+#define SCM_NORETURN __attribute__ ((noreturn))
+#else
+#define SCM_NORETURN
+#endif
+
+/* The macro SCM_UNUSED indicates that a function, function argument or
+ * variable may potentially be unused.
+ * Examples:
+ *   1) static int unused_function (char arg) SCM_UNUSED;
+ *   2) int foo (char unused_argument SCM_UNUSED);
+ *   3) int unused_variable SCM_UNUSED;
+ */
+#ifdef __GNUC__
+#define SCM_UNUSED __attribute__ ((unused))
+#else
+#define SCM_UNUSED
+#endif
+
+
 /* {Supported Options}
  *
  * These may be defined or undefined.
@@ -177,6 +209,14 @@
 #define SCM_DEBUG_INTERRUPTS SCM_DEBUG
 #endif
 
+/* If SCM_DEBUG_PAIR_ACCESSES is set to 1, accesses to cons cells will be
+ * exhaustively checked.  Note:  If this option is enabled, guile will run
+ * slower than normally.
+ */
+#ifndef SCM_DEBUG_PAIR_ACCESSES
+#define SCM_DEBUG_PAIR_ACCESSES SCM_DEBUG
+#endif
+
 /* If SCM_DEBUG_REST_ARGUMENT is set to 1, functions that take rest arguments
  * will check whether the rest arguments are actually passed as a proper list.
  * Otherwise, if SCM_DEBUG_REST_ARGUMENT is 0, functions that take rest
diff --git a/libguile/backtrace.c b/libguile/backtrace.c
index a602d9139..8ddc473df 100644
--- a/libguile/backtrace.c
+++ b/libguile/backtrace.c
@@ -1,5 +1,5 @@
 /* Printing of backtraces and error messages
- * Copyright (C) 1996, 1997, 1998, 1999, 2000 Free Software Foundation
+ * Copyright (C) 1996,1997,1998,1999,2000,2001 Free Software Foundation
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -216,7 +216,7 @@ struct display_error_handler_data {
    try to print all objects, we would enter an infinite loop. */
 static SCM
 display_error_handler (struct display_error_handler_data *data,
-		       SCM tag, SCM args)
+		       SCM tag, SCM args SCM_UNUSED)
 {
   SCM print_state = scm_make_print_state ();
   scm_puts ("\nException during displaying of ", data->port);
diff --git a/libguile/continuations.c b/libguile/continuations.c
index 7b33d7248..49f2890d8 100644
--- a/libguile/continuations.c
+++ b/libguile/continuations.c
@@ -1,4 +1,4 @@
-/*	Copyright (C) 1995,1996,1998, 2000 Free Software Foundation, Inc.
+/* Copyright (C) 1995,1996,1998,2000,2001 Free Software Foundation, Inc.
  * 
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -94,7 +94,7 @@ continuation_free (SCM obj)
 }
 
 static int
-continuation_print (SCM obj, SCM port, scm_print_state *state)
+continuation_print (SCM obj, SCM port, scm_print_state *state SCM_UNUSED)
 {
   scm_contregs_t *continuation = SCM_CONTREGS (obj);
 
diff --git a/libguile/debug.c b/libguile/debug.c
index dc47c9dbc..bd0b4ba7f 100644
--- a/libguile/debug.c
+++ b/libguile/debug.c
@@ -557,7 +557,7 @@ scm_m_start_stack (SCM exp, SCM env)
 scm_bits_t scm_tc16_debugobj;
 
 static int
-debugobj_print (SCM obj, SCM port, scm_print_state *pstate)
+debugobj_print (SCM obj, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   scm_puts ("#<debug-object ", port);
   scm_intprint ((int) SCM_DEBUGOBJ_FRAME (obj), 16, port);
diff --git a/libguile/dynwind.c b/libguile/dynwind.c
index bc4c72575..24d2e415f 100644
--- a/libguile/dynwind.c
+++ b/libguile/dynwind.c
@@ -1,4 +1,4 @@
-/*	Copyright (C) 1995, 1996, 1998, 1999, 2000 Free Software Foundation, Inc.
+/* Copyright (C) 1995,1996,1998,1999,2000,2001 Free Software Foundation, Inc.
  * 
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -147,7 +147,7 @@ SCM_DEFINE (scm_dynamic_wind, "dynamic-wind", 3, 0, 0,
 static scm_bits_t tc16_guards;
 
 static int
-guards_print (SCM exp, SCM port, scm_print_state *pstate)
+guards_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   scm_puts ("#<guards ", port);
   scm_intprint (SCM_UNPACK (SCM_CDR (exp)), 16, port);
diff --git a/libguile/environments.c b/libguile/environments.c
index eecf4fe3f..211ce2816 100644
--- a/libguile/environments.c
+++ b/libguile/environments.c
@@ -506,7 +506,7 @@ observer_mark (SCM observer)
 
 
 static int
-observer_print (SCM type, SCM port, scm_print_state *pstate)
+observer_print (SCM type, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   SCM address = scm_ulong2num (SCM_UNPACK (type));
   SCM base16 = scm_number_to_string (address, SCM_MAKINUM (16));
@@ -752,7 +752,7 @@ core_environments_mark (SCM env)
 
 
 static void
-core_environments_finalize (SCM env)
+core_environments_finalize (SCM env SCM_UNUSED)
 {
 }
 
@@ -975,7 +975,7 @@ leaf_environment_set_x (SCM env, SCM sym, SCM val)
 
 
 static SCM
-leaf_environment_cell(SCM env, SCM sym, int for_write)
+leaf_environment_cell (SCM env, SCM sym, int for_write SCM_UNUSED)
 {
   SCM obarray = LEAF_ENVIRONMENT (env)->obarray;
   SCM binding = obarray_retrieve (obarray, sym);
@@ -1002,7 +1002,7 @@ leaf_environment_free (SCM env)
 
 
 static int
-leaf_environment_print (SCM type, SCM port, scm_print_state *pstate)
+leaf_environment_print (SCM type, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   SCM address = scm_ulong2num (SCM_UNPACK (type));
   SCM base16 = scm_number_to_string (address, SCM_MAKINUM (16));
@@ -1363,7 +1363,7 @@ eval_environment_free (SCM env)
 
 
 static int
-eval_environment_print (SCM type, SCM port, scm_print_state *pstate)
+eval_environment_print (SCM type, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   SCM address = scm_ulong2num (SCM_UNPACK (type));
   SCM base16 = scm_number_to_string (address, SCM_MAKINUM (16));
@@ -1395,7 +1395,7 @@ void *scm_type_eval_environment = &eval_environment_funcs;
 
 
 static void
-eval_environment_observer (SCM caller, SCM eval_env)
+eval_environment_observer (SCM caller SCM_UNUSED, SCM eval_env)
 {
   SCM obarray = EVAL_ENVIRONMENT (eval_env)->obarray;
 
@@ -1687,7 +1687,9 @@ import_environment_fold (SCM env, scm_environment_folder proc, SCM data, SCM ini
 
 
 static SCM
-import_environment_define (SCM env, SCM sym, SCM val)
+import_environment_define (SCM env SCM_UNUSED,
+			   SCM sym SCM_UNUSED,
+			   SCM val SCM_UNUSED)
 #define FUNC_NAME "import_environment_define"
 {
   return SCM_ENVIRONMENT_BINDING_IMMUTABLE;
@@ -1696,7 +1698,8 @@ import_environment_define (SCM env, SCM sym, SCM val)
 
 
 static SCM
-import_environment_undefine (SCM env, SCM sym)
+import_environment_undefine (SCM env SCM_UNUSED,
+			     SCM sym SCM_UNUSED)
 #define FUNC_NAME "import_environment_undefine"
 {
   return SCM_ENVIRONMENT_BINDING_IMMUTABLE;
@@ -1779,7 +1782,8 @@ import_environment_free (SCM env)
 
 
 static int
-import_environment_print (SCM type, SCM port, scm_print_state *pstate)
+import_environment_print (SCM type, SCM port, 
+			  scm_print_state *pstate SCM_UNUSED)
 {
   SCM address = scm_ulong2num (SCM_UNPACK (type));
   SCM base16 = scm_number_to_string (address, SCM_MAKINUM (16));
@@ -1811,7 +1815,7 @@ void *scm_type_import_environment = &import_environment_funcs;
 
 
 static void
-import_environment_observer (SCM caller, SCM import_env)
+import_environment_observer (SCM caller SCM_UNUSED, SCM import_env)
 {
   core_environments_broadcast (import_env);
 }
@@ -1997,7 +2001,9 @@ export_environment_fold (SCM env, scm_environment_folder proc, SCM data, SCM ini
 
 
 static SCM
-export_environment_define (SCM env, SCM sym, SCM val)
+export_environment_define (SCM env SCM_UNUSED, 
+			   SCM sym SCM_UNUSED, 
+			   SCM val SCM_UNUSED)
 #define FUNC_NAME "export_environment_define"
 {
   return SCM_ENVIRONMENT_BINDING_IMMUTABLE;
@@ -2006,7 +2012,7 @@ export_environment_define (SCM env, SCM sym, SCM val)
 
 
 static SCM
-export_environment_undefine (SCM env, SCM sym)
+export_environment_undefine (SCM env SCM_UNUSED, SCM sym SCM_UNUSED)
 #define FUNC_NAME "export_environment_undefine"
 {
   return SCM_ENVIRONMENT_BINDING_IMMUTABLE;
@@ -2082,7 +2088,8 @@ export_environment_free (SCM env)
 
 
 static int
-export_environment_print (SCM type, SCM port, scm_print_state *pstate)
+export_environment_print (SCM type, SCM port,
+			  scm_print_state *pstate SCM_UNUSED)
 {
   SCM address = scm_ulong2num (SCM_UNPACK (type));
   SCM base16 = scm_number_to_string (address, SCM_MAKINUM (16));
@@ -2114,7 +2121,7 @@ void *scm_type_export_environment = &export_environment_funcs;
 
 
 static void
-export_environment_observer (SCM caller, SCM export_env)
+export_environment_observer (SCM caller SCM_UNUSED, SCM export_env)
 {
   core_environments_broadcast (export_env);
 }
diff --git a/libguile/error.h b/libguile/error.h
index cfdc604a1..37b8ee342 100644
--- a/libguile/error.h
+++ b/libguile/error.h
@@ -1,8 +1,8 @@
 /* classes: h_files */
 
-#ifndef ERRORH
-#define ERRORH
-/*	Copyright (C) 1995,1996,1997,1998, 2000 Free Software Foundation, Inc.
+#ifndef SCM_ERROR_H
+#define SCM_ERROR_H
+/* Copyright (C) 1995,1996,1997,1998,2000,2001 Free Software Foundation, Inc.
  * 
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -50,15 +50,6 @@ extern int scm_ints_disabled;
 
 
 
-/* GCC can be told that a function doesn't return; this helps it do
-   better error checking (for uninitialized variable use, for
-   example), and some optimization.  */
-#ifdef __GNUC__
-#define SCM_NORETURN __attribute__ ((noreturn))
-#else
-#define SCM_NORETURN
-#endif
-
 extern void scm_error (SCM key, const char *subr, const char *message,
                              SCM args, SCM rest) SCM_NORETURN;
 extern SCM scm_error_scm (SCM key, SCM subr, SCM message,
@@ -91,7 +82,7 @@ extern SCM scm_wta (SCM arg, const char *pos, const char *s_subr);
 
 #endif  /* SCM_DEBUG_DEPRECATED == 0 */
 
-#endif  /* ERRORH */
+#endif  /* SCM_ERROR_H */
 
 /*
   Local Variables:
diff --git a/libguile/eval.c b/libguile/eval.c
index ee577c1e1..a45ae0851 100644
--- a/libguile/eval.c
+++ b/libguile/eval.c
@@ -518,7 +518,7 @@ SCM_SYNTAX(s_quote,"quote", scm_makmmacro, scm_m_quote);
 SCM_GLOBAL_SYMBOL(scm_sym_quote, s_quote);
 
 SCM 
-scm_m_quote (SCM xorig, SCM env)
+scm_m_quote (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM x = scm_copy_tree (SCM_CDR (xorig));
 
@@ -532,7 +532,7 @@ SCM_SYNTAX(s_begin, "begin", scm_makmmacro, scm_m_begin);
 SCM_GLOBAL_SYMBOL(scm_sym_begin, s_begin);
 
 SCM 
-scm_m_begin (SCM xorig, SCM env)
+scm_m_begin (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM_ASSYNT (scm_ilength (SCM_CDR (xorig)) >= 1, scm_s_expression, s_begin);
   return scm_cons (SCM_IM_BEGIN, SCM_CDR (xorig));
@@ -542,7 +542,7 @@ SCM_SYNTAX(s_if, "if", scm_makmmacro, scm_m_if);
 SCM_GLOBAL_SYMBOL(scm_sym_if, s_if);
 
 SCM 
-scm_m_if (SCM xorig, SCM env)
+scm_m_if (SCM xorig, SCM env SCM_UNUSED)
 {
   long len = scm_ilength (SCM_CDR (xorig));
   SCM_ASSYNT (len >= 2 && len <= 3, scm_s_expression, "if");
@@ -556,7 +556,7 @@ const char scm_s_set_x[] = "set!";
 SCM_GLOBAL_SYMBOL(scm_sym_set_x, scm_s_set_x);
 
 SCM 
-scm_m_set_x (SCM xorig, SCM env)
+scm_m_set_x (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM x = SCM_CDR (xorig);
   SCM_ASSYNT (2 == scm_ilength (x), scm_s_expression, scm_s_set_x);
@@ -569,7 +569,7 @@ SCM_SYNTAX(s_and, "and", scm_makmmacro, scm_m_and);
 SCM_GLOBAL_SYMBOL(scm_sym_and, s_and);
 
 SCM 
-scm_m_and (SCM xorig, SCM env)
+scm_m_and (SCM xorig, SCM env SCM_UNUSED)
 {
   long len = scm_ilength (SCM_CDR (xorig));
   SCM_ASSYNT (len >= 0, scm_s_test, s_and);
@@ -583,7 +583,7 @@ SCM_SYNTAX(s_or,"or", scm_makmmacro, scm_m_or);
 SCM_GLOBAL_SYMBOL(scm_sym_or,s_or);
 
 SCM 
-scm_m_or (SCM xorig, SCM env)
+scm_m_or (SCM xorig, SCM env SCM_UNUSED)
 {
   long len = scm_ilength (SCM_CDR (xorig));
   SCM_ASSYNT (len >= 0, scm_s_test, s_or);
@@ -598,7 +598,7 @@ SCM_SYNTAX(s_case, "case", scm_makmmacro, scm_m_case);
 SCM_GLOBAL_SYMBOL(scm_sym_case, s_case);
 
 SCM 
-scm_m_case (SCM xorig, SCM env)
+scm_m_case (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM proc, cdrx = scm_list_copy (SCM_CDR (xorig)), x = cdrx;
   SCM_ASSYNT (scm_ilength (x) >= 2, scm_s_clauses, s_case);
@@ -620,7 +620,7 @@ SCM_GLOBAL_SYMBOL(scm_sym_cond, s_cond);
 
 
 SCM 
-scm_m_cond (SCM xorig, SCM env)
+scm_m_cond (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM arg1, cdrx = scm_list_copy (SCM_CDR (xorig)), x = cdrx;
   long len = scm_ilength (x);
@@ -663,7 +663,7 @@ scm_c_improper_memq (SCM obj, SCM list)
 }
 
 SCM 
-scm_m_lambda (SCM xorig, SCM env)
+scm_m_lambda (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM proc, x = SCM_CDR (xorig);
   if (scm_ilength (x) < 2)
@@ -710,7 +710,7 @@ SCM_GLOBAL_SYMBOL(scm_sym_letstar,s_letstar);
 
 
 SCM 
-scm_m_letstar (SCM xorig, SCM env)
+scm_m_letstar (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM x = SCM_CDR (xorig), arg1, proc, vars = SCM_EOL, *varloc = &vars;
   long len = scm_ilength (x);
@@ -750,7 +750,7 @@ SCM_SYNTAX(s_do, "do", scm_makmmacro, scm_m_do);
 SCM_GLOBAL_SYMBOL(scm_sym_do, s_do);
 
 SCM 
-scm_m_do (SCM xorig, SCM env)
+scm_m_do (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM x = SCM_CDR (xorig), arg1, proc;
   SCM vars = SCM_EOL, inits = SCM_EOL, steps = SCM_EOL;
@@ -852,7 +852,7 @@ SCM_SYNTAX (s_delay, "delay", scm_makmmacro, scm_m_delay);
 SCM_GLOBAL_SYMBOL (scm_sym_delay, s_delay);
 
 SCM 
-scm_m_delay (SCM xorig, SCM env)
+scm_m_delay (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM_ASSYNT (scm_ilength (xorig) == 2, scm_s_expression, s_delay);
   return scm_cons2 (SCM_IM_DELAY, SCM_EOL, SCM_CDR (xorig));
@@ -912,7 +912,7 @@ scm_m_define (SCM x, SCM env)
 /* end of acros */
 
 static SCM
-scm_m_letrec1 (SCM op, SCM imm, SCM xorig, SCM env)
+scm_m_letrec1 (SCM op, SCM imm, SCM xorig, SCM env SCM_UNUSED)
 {
   SCM cdrx = SCM_CDR (xorig);	/* locally mutable version of form */
   char *what = SCM_SYMBOL_CHARS (SCM_CAR (xorig));
@@ -1022,7 +1022,7 @@ SCM_GLOBAL_SYMBOL (scm_sym_atapply, s_atapply);
 SCM_GLOBAL_SYMBOL (scm_sym_apply, s_atapply + 1);
 
 SCM 
-scm_m_apply (SCM xorig, SCM env)
+scm_m_apply (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM_ASSYNT (scm_ilength (SCM_CDR (xorig)) == 2, scm_s_expression, s_atapply);
   return scm_cons (SCM_IM_APPLY, SCM_CDR (xorig));
@@ -1034,7 +1034,7 @@ SCM_GLOBAL_SYMBOL(scm_sym_atcall_cc,s_atcall_cc);
 
 
 SCM 
-scm_m_cont (SCM xorig, SCM env)
+scm_m_cont (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM_ASSYNT (scm_ilength (SCM_CDR (xorig)) == 1,
 	      scm_s_expression, s_atcall_cc);
@@ -1049,7 +1049,7 @@ SCM_GLOBAL_SYMBOL (scm_lisp_t, "t");
 SCM_SYNTAX (s_nil_cond, "nil-cond", scm_makmmacro, scm_m_nil_cond);
 
 SCM
-scm_m_nil_cond (SCM xorig, SCM env)
+scm_m_nil_cond (SCM xorig, SCM env SCM_UNUSED)
 {
   long len = scm_ilength (SCM_CDR (xorig));
   SCM_ASSYNT (len >= 1 && (len & 1) == 1, scm_s_expression, "nil-cond");
@@ -1059,7 +1059,7 @@ scm_m_nil_cond (SCM xorig, SCM env)
 SCM_SYNTAX (s_nil_ify, "nil-ify", scm_makmmacro, scm_m_nil_ify);
 
 SCM
-scm_m_nil_ify (SCM xorig, SCM env)
+scm_m_nil_ify (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM_ASSYNT (scm_ilength (SCM_CDR (xorig)) == 1, scm_s_expression, "nil-ify");
   return scm_cons (SCM_IM_NIL_IFY, SCM_CDR (xorig));
@@ -1068,7 +1068,7 @@ scm_m_nil_ify (SCM xorig, SCM env)
 SCM_SYNTAX (s_t_ify, "t-ify", scm_makmmacro, scm_m_t_ify);
 
 SCM
-scm_m_t_ify (SCM xorig, SCM env)
+scm_m_t_ify (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM_ASSYNT (scm_ilength (SCM_CDR (xorig)) == 1, scm_s_expression, "t-ify");
   return scm_cons (SCM_IM_T_IFY, SCM_CDR (xorig));
@@ -1077,7 +1077,7 @@ scm_m_t_ify (SCM xorig, SCM env)
 SCM_SYNTAX (s_0_cond, "0-cond", scm_makmmacro, scm_m_0_cond);
 
 SCM
-scm_m_0_cond (SCM xorig, SCM env)
+scm_m_0_cond (SCM xorig, SCM env SCM_UNUSED)
 {
   long len = scm_ilength (SCM_CDR (xorig));
   SCM_ASSYNT (len >= 1 && (len & 1) == 1, scm_s_expression, "0-cond");
@@ -1087,7 +1087,7 @@ scm_m_0_cond (SCM xorig, SCM env)
 SCM_SYNTAX (s_0_ify, "0-ify", scm_makmmacro, scm_m_0_ify);
 
 SCM
-scm_m_0_ify (SCM xorig, SCM env)
+scm_m_0_ify (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM_ASSYNT (scm_ilength (SCM_CDR (xorig)) == 1, scm_s_expression, "0-ify");
   return scm_cons (SCM_IM_0_IFY, SCM_CDR (xorig));
@@ -1096,7 +1096,7 @@ scm_m_0_ify (SCM xorig, SCM env)
 SCM_SYNTAX (s_1_ify, "1-ify", scm_makmmacro, scm_m_1_ify);
 
 SCM
-scm_m_1_ify (SCM xorig, SCM env)
+scm_m_1_ify (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM_ASSYNT (scm_ilength (SCM_CDR (xorig)) == 1, scm_s_expression, "1-ify");
   return scm_cons (SCM_IM_1_IFY, SCM_CDR (xorig));
@@ -1105,7 +1105,7 @@ scm_m_1_ify (SCM xorig, SCM env)
 SCM_SYNTAX (s_atfop, "@fop", scm_makmmacro, scm_m_atfop);
 
 SCM
-scm_m_atfop (SCM xorig, SCM env)
+scm_m_atfop (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM x = SCM_CDR (xorig), var;
   SCM_ASSYNT (scm_ilength (x) >= 1, scm_s_expression, "@fop");
@@ -1148,7 +1148,7 @@ SCM_SYNTAX (s_at_call_with_values, "@call-with-values", scm_makmmacro, scm_m_at_
 SCM_GLOBAL_SYMBOL(scm_sym_at_call_with_values, s_at_call_with_values);
 
 SCM
-scm_m_at_call_with_values (SCM xorig, SCM env)
+scm_m_at_call_with_values (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM_ASSYNT (scm_ilength (SCM_CDR (xorig)) == 2,
 	      scm_s_expression, s_at_call_with_values);
diff --git a/libguile/evalext.c b/libguile/evalext.c
index a36ef687b..b19f94c21 100644
--- a/libguile/evalext.c
+++ b/libguile/evalext.c
@@ -1,4 +1,4 @@
-/*	Copyright (C) 1998, 1999, 2000 Free Software Foundation, Inc.
+/* Copyright (C) 1998,1999,2000,2001 Free Software Foundation, Inc.
  * 
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -56,7 +56,7 @@
 SCM_SYMBOL (scm_sym_setter, "setter");
 
 SCM 
-scm_m_generalized_set_x (SCM xorig, SCM env)
+scm_m_generalized_set_x (SCM xorig, SCM env SCM_UNUSED)
 {
   SCM x = SCM_CDR (xorig);
   SCM_ASSYNT (2 == scm_ilength (x), scm_s_expression, scm_s_set_x);
diff --git a/libguile/filesys.c b/libguile/filesys.c
index 0960300e6..56b4737d1 100644
--- a/libguile/filesys.c
+++ b/libguile/filesys.c
@@ -783,7 +783,7 @@ SCM_DEFINE (scm_closedir, "closedir", 1, 0, 0,
 
 
 static int 
-scm_dir_print (SCM exp, SCM port, scm_print_state *pstate)
+scm_dir_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   scm_puts ("#<", port);
   if (!SCM_DIR_OPEN_P (exp))
diff --git a/libguile/fluids.c b/libguile/fluids.c
index 718dc5f3f..b3a12d666 100644
--- a/libguile/fluids.c
+++ b/libguile/fluids.c
@@ -96,7 +96,7 @@ scm_copy_fluids (scm_root_state *root_state)
 }
 
 static int
-fluid_print (SCM exp, SCM port, scm_print_state *pstate)
+fluid_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   scm_puts ("#<fluid ", port);
   scm_intprint ((int) SCM_FLUID_NUM (exp), 10, port);
diff --git a/libguile/fports.c b/libguile/fports.c
index acf7b3f2f..f5c63d0d0 100644
--- a/libguile/fports.c
+++ b/libguile/fports.c
@@ -1,4 +1,4 @@
-/*	Copyright (C) 1995,1996,1997,1998,1999,2000,2001 Free Software Foundation, Inc.
+/* Copyright (C) 1995,1996,1997,1998,1999,2000,2001 Free Software Foundation, Inc.
  * 
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -441,7 +441,7 @@ fport_input_waiting (SCM port)
 
 
 static int 
-fport_print (SCM exp, SCM port, scm_print_state *pstate)
+fport_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   scm_puts ("#<", port);
   scm_print_port_mode (exp, port);    
diff --git a/libguile/gc.c b/libguile/gc.c
index 48f688b93..29eee3392 100644
--- a/libguile/gc.c
+++ b/libguile/gc.c
@@ -108,11 +108,19 @@ scm_bits_t scm_tc16_allocated;
  */
 unsigned int scm_debug_cell_accesses_p = 1;
 
+/* Set this to 0 if no additional gc's shall be performed, otherwise set it to
+ * the number of cell accesses after which a gc shall be called.
+ */
+static unsigned int debug_cells_gc_interval = 0;
+
 
 /* Assert that the given object is a valid reference to a valid cell.  This
  * test involves to determine whether the object is a cell pointer, whether
  * this pointer actually points into a heap segment and whether the cell
- * pointed to is not a free cell.
+ * pointed to is not a free cell.  Further, additional garbage collections may
+ * get executed after a user defined number of cell accesses.  This helps to
+ * find places in the C code where references are dropped for extremely short
+ * periods.
  */
 void
 scm_assert_cell_valid (SCM cell)
@@ -146,6 +154,24 @@ scm_assert_cell_valid (SCM cell)
                        (unsigned long) SCM_UNPACK (cell));
 	      abort ();
 	    }
+
+	  /* If desired, perform additional garbage collections after a user
+	   * defined number of cell accesses.
+	   */
+	  if (debug_cells_gc_interval)
+	    {
+	      static unsigned int counter = 0;
+	      
+	      if (counter != 0)
+		{
+		  --counter;
+		}
+	      else
+		{
+		  counter = debug_cells_gc_interval;
+		  scm_igc ("scm_assert_cell_valid");
+		}
+	    }
 	}
       already_running = 0;  /* re-enable */
     }
@@ -155,7 +181,11 @@ scm_assert_cell_valid (SCM cell)
 SCM_DEFINE (scm_set_debug_cell_accesses_x, "set-debug-cell-accesses!", 1, 0, 0,
 	    (SCM flag),
 	    "If @var{flag} is @code{#f}, cell access checking is disabled.\n"
-	    "If @var{flag} is @code{#t}, cell access checking is enabled.\n"
+	    "If @var{flag} is @code{#t}, cell access checking is enabled,\n"
+	    "but no additional calls to garbage collection are issued.\n"
+	    "If @var{flag} is a number, cell access checking is enabled,\n"
+	    "with an additional garbage collection after the given\n"
+	    "number of cell accesses.\n"
 	    "This procedure only exists when the compile-time flag\n"
 	    "@code{SCM_DEBUG_CELL_ACCESSES} was set to 1.")
 #define FUNC_NAME s_scm_set_debug_cell_accesses_x
@@ -163,6 +193,12 @@ SCM_DEFINE (scm_set_debug_cell_accesses_x, "set-debug-cell-accesses!", 1, 0, 0,
   if (SCM_FALSEP (flag)) {
     scm_debug_cell_accesses_p = 0;
   } else if (SCM_EQ_P (flag, SCM_BOOL_T)) {
+    debug_cells_gc_interval = 0;
+    scm_debug_cell_accesses_p = 1;
+  } else if (SCM_INUMP (flag)) {
+    long int f = SCM_INUM (flag);
+    if (f <= 0) SCM_OUT_OF_RANGE (1, flag);
+    debug_cells_gc_interval = f;
     scm_debug_cell_accesses_p = 1;
   } else {
     SCM_WRONG_TYPE_ARG (1, flag);
@@ -824,7 +860,7 @@ SCM_DEFINE (scm_gc_stats, "gc-stats", 0, 0, 0,
 
 
 static void
-gc_start_stats (const char *what)
+gc_start_stats (const char *what SCM_UNUSED)
 {
   t_before_gc = scm_c_get_internal_run_time ();
   scm_gc_cells_swept = 0;
@@ -2449,19 +2485,19 @@ alloc_some_heap (scm_freelist_t *freelist, policy_on_error error_policy)
  */
 
 void
-scm_remember_upto_here_1 (SCM obj)
+scm_remember_upto_here_1 (SCM obj SCM_UNUSED)
 {
   /* Empty.  Protects a single object from garbage collection. */
 }
 
 void
-scm_remember_upto_here_2 (SCM obj1, SCM obj2)
+scm_remember_upto_here_2 (SCM obj1 SCM_UNUSED, SCM obj2 SCM_UNUSED)
 {
   /* Empty.  Protects two objects from garbage collection. */
 }
 
 void
-scm_remember_upto_here (SCM obj, ...)
+scm_remember_upto_here (SCM obj SCM_UNUSED, ...)
 {
   /* Empty.  Protects any number of objects from garbage collection. */
 }
@@ -2828,9 +2864,41 @@ gc_async_thunk (void)
  * gc_async_thunk).
  */
 static void *
-mark_gc_async (void * hook_data, void *func_data, void *data)
+mark_gc_async (void * hook_data SCM_UNUSED,
+	       void *func_data SCM_UNUSED,
+	       void *data SCM_UNUSED)
 {
+  /* If cell access debugging is enabled, the user may choose to perform
+   * additional garbage collections after an arbitrary number of cell
+   * accesses.  We don't want the scheme level after-gc-hook to be performed
+   * for each of these garbage collections for the following reason: The
+   * execution of the after-gc-hook causes cell accesses itself.  Thus, if the
+   * after-gc-hook was performed with every gc, and if the gc was performed
+   * after a very small number of cell accesses, then the number of cell
+   * accesses during the execution of the after-gc-hook will suffice to cause
+   * the execution of the next gc.  Then, guile would keep executing the
+   * after-gc-hook over and over again, and would never come to do other
+   * things.
+   * 
+   * To overcome this problem, if cell access debugging with additional
+   * garbage collections is enabled, the after-gc-hook is never run by the
+   * garbage collecter.  When running guile with cell access debugging and the
+   * execution of the after-gc-hook is desired, then it is necessary to run
+   * the hook explicitly from the user code.  This has the effect, that from
+   * the scheme level point of view it seems that garbage collection is
+   * performed with a much lower frequency than it actually is.  Obviously,
+   * this will not work for code that depends on a fixed one to one
+   * relationship between the execution counts of the C level garbage
+   * collection hooks and the execution count of the scheme level
+   * after-gc-hook.
+   */
+#if (SCM_DEBUG_CELL_ACCESSES == 1)
+  if (debug_cells_gc_interval == 0)
+    scm_system_async_mark (gc_async);
+#else
   scm_system_async_mark (gc_async);
+#endif
+
   return NULL;
 }
 
diff --git a/libguile/gh_init.c b/libguile/gh_init.c
index 5dbc7daad..62b684d29 100644
--- a/libguile/gh_init.c
+++ b/libguile/gh_init.c
@@ -1,5 +1,5 @@
-/*      Copyright (C) 1995,1996,1997, 2000 Free Software Foundation, Inc.
-
+/* Copyright (C) 1995,1996,1997,2000,2001 Free Software Foundation, Inc.
+ *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2, or (at your option)
@@ -94,7 +94,7 @@ gh_catch (SCM tag, scm_catch_body_t body, void *body_data,
 }
 
 SCM 
-gh_standard_handler (void *data, SCM tag, SCM throw_args)
+gh_standard_handler (void *data SCM_UNUSED, SCM tag, SCM throw_args SCM_UNUSED)
 {
   fprintf (stderr, "\nJust got an error; tag is\n        ");
   scm_display (tag, scm_current_output_port ());
diff --git a/libguile/goops.c b/libguile/goops.c
index a85f4975c..4ea756a10 100644
--- a/libguile/goops.c
+++ b/libguile/goops.c
@@ -1047,7 +1047,7 @@ slot_definition_using_name (SCM class, SCM slot_name)
 }
 
 static SCM
-get_slot_value (SCM class, SCM obj, SCM slotdef)
+get_slot_value (SCM class SCM_UNUSED, SCM obj, SCM slotdef)
 {
   SCM access = SCM_CDDR (slotdef);
   /* Two cases here:
@@ -1084,7 +1084,7 @@ get_slot_value_using_name (SCM class, SCM obj, SCM slot_name)
 }
 
 static SCM
-set_slot_value (SCM class, SCM obj, SCM slotdef, SCM value)
+set_slot_value (SCM class SCM_UNUSED, SCM obj, SCM slotdef, SCM value)
 {
   SCM access = SCM_CDDR (slotdef);
   /* Two cases here:
@@ -1125,7 +1125,7 @@ set_slot_value_using_name (SCM class, SCM obj, SCM slot_name, SCM value)
 }
 
 static SCM
-test_slot_existence (SCM class, SCM obj, SCM slot_name)
+test_slot_existence (SCM class SCM_UNUSED, SCM obj, SCM slot_name)
 {
   register SCM l;
 
@@ -1518,7 +1518,7 @@ purgatory (void *args)
 }
 
 void
-scm_change_object_class (SCM obj, SCM old_class, SCM new_class)
+scm_change_object_class (SCM obj, SCM old_class SCM_UNUSED, SCM new_class)
 {
   if (!burnin (obj))
     scm_internal_dynamic_wind (go_to_hell, purgatory, go_to_heaven,
@@ -1868,7 +1868,7 @@ SCM_VARIABLE_INIT (var_compute_applicable_methods, "compute-applicable-methods",
 SCM_SYNTAX (s_atslot_ref, "@slot-ref", scm_makmmacro, scm_m_atslot_ref);
 
 SCM
-scm_m_atslot_ref (SCM xorig, SCM env)
+scm_m_atslot_ref (SCM xorig, SCM env SCM_UNUSED)
 #define FUNC_NAME s_atslot_ref
 {
   SCM x = SCM_CDR (xorig);
@@ -1882,7 +1882,7 @@ scm_m_atslot_ref (SCM xorig, SCM env)
 SCM_SYNTAX (s_atslot_set_x, "@slot-set!", scm_makmmacro, scm_m_atslot_set_x);
 
 SCM
-scm_m_atslot_set_x (SCM xorig, SCM env)
+scm_m_atslot_set_x (SCM xorig, SCM env SCM_UNUSED)
 #define FUNC_NAME s_atslot_set_x
 {
   SCM x = SCM_CDR (xorig);
@@ -2413,7 +2413,8 @@ create_port_classes (void)
 }
 
 static SCM
-make_struct_class (void *closure, SCM key, SCM data, SCM prev)
+make_struct_class (void *closure SCM_UNUSED, SCM key SCM_UNUSED, 
+		   SCM data, SCM prev SCM_UNUSED)
 {
   if (SCM_NFALSEP (SCM_STRUCT_TABLE_NAME (data)))
     SCM_SET_STRUCT_TABLE_CLASS (data,
@@ -2499,7 +2500,7 @@ SCM_KEYWORD (k_accessor, "accessor");
 SCM_KEYWORD (k_getter, "getter");
 
 static SCM
-default_setter (SCM obj, SCM c)
+default_setter (SCM obj SCM_UNUSED, SCM c SCM_UNUSED)
 {
   scm_misc_error ("slot-set!", "read-only slot", SCM_EOL);
   return 0;
diff --git a/libguile/guardians.c b/libguile/guardians.c
index c41f048bd..b62d8088d 100644
--- a/libguile/guardians.c
+++ b/libguile/guardians.c
@@ -184,7 +184,7 @@ guardian_free (SCM ptr)
 
 
 static int
-guardian_print (SCM guardian, SCM port, scm_print_state *pstate)
+guardian_print (SCM guardian, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   guardian_t *g = GUARDIAN (guardian);
   
@@ -428,7 +428,9 @@ SCM_DEFINE (scm_destroy_guardian_x, "destroy-guardian!", 1, 0, 0,
             
 /* called before gc mark phase begins to initialise the live guardian list. */
 static void *
-guardian_gc_init (void *dummy1, void *dummy2, void *dummy3)
+guardian_gc_init (void *dummy1 SCM_UNUSED,
+		  void *dummy2 SCM_UNUSED,
+		  void *dummy3 SCM_UNUSED)
 {
   greedy_guardians = sharing_guardians = NULL;
 
@@ -530,7 +532,9 @@ mark_and_zombify (guardian_t *g)
    phases.  for each marked guardian, it moves any unmarked object in
    its live list (tconc) to its zombie list (tconc).  */
 static void *
-guardian_zombify (void *dummy1, void *dummy2, void *dummy3)
+guardian_zombify (void *dummy1 SCM_UNUSED,
+		  void *dummy2 SCM_UNUSED,
+		  void *dummy3 SCM_UNUSED)
 {
   guardian_t *last_greedy_guardian = NULL;
   guardian_t *last_sharing_guardian = NULL;
@@ -588,7 +592,9 @@ guardian_zombify (void *dummy1, void *dummy2, void *dummy3)
 }
 
 static void *
-whine_about_self_centered_zombies (void *dummy1, void *dummy2, void *dummy3)
+whine_about_self_centered_zombies (void *dummy1 SCM_UNUSED,
+				   void *dummy2 SCM_UNUSED,
+				   void *dummy3 SCM_UNUSED)
 {
   if (! SCM_NULLP (SCM_CDR (self_centered_zombies)))
     {
diff --git a/libguile/guile.c b/libguile/guile.c
index aed12f4f8..21be17871 100644
--- a/libguile/guile.c
+++ b/libguile/guile.c
@@ -1,4 +1,4 @@
-/*	Copyright (C) 1996, 1997, 2000 Free Software Foundation, Inc.
+/* Copyright (C) 1996,1997,2000,2001 Free Software Foundation, Inc.
  * 
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -61,7 +61,7 @@
 GDB_INTERFACE;
 
 static void
-inner_main (void *closure, int argc, char **argv)
+inner_main (void *closure SCM_UNUSED, int argc, char **argv)
 {
   /* module initializations would go here */
   scm_shell (argc, argv);
diff --git a/libguile/init.c b/libguile/init.c
index 0cb54f3ad..0c7e04578 100644
--- a/libguile/init.c
+++ b/libguile/init.c
@@ -279,7 +279,9 @@ stream_body (void *data)
 
 /* exception handler for stream_body.  */
 static SCM
-stream_handler (void *data, SCM tag, SCM throw_args)
+stream_handler (void *data SCM_UNUSED,
+		SCM tag SCM_UNUSED,
+		SCM throw_args SCM_UNUSED)
 {
   return SCM_BOOL_F;
 }
diff --git a/libguile/keywords.c b/libguile/keywords.c
index 53f457c1a..cea7ac526 100644
--- a/libguile/keywords.c
+++ b/libguile/keywords.c
@@ -59,7 +59,7 @@
 scm_bits_t scm_tc16_keyword;
 
 static int
-keyword_print (SCM exp, SCM port, scm_print_state *pstate)
+keyword_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   scm_puts ("#:", port);
   scm_print_symbol_name (SCM_SYMBOL_CHARS (SCM_CDR (exp)) + 1,
diff --git a/libguile/mallocs.c b/libguile/mallocs.c
index 0a6a1db61..168f0632e 100644
--- a/libguile/mallocs.c
+++ b/libguile/mallocs.c
@@ -74,7 +74,7 @@ malloc_free (SCM ptr)
 
 
 static int
-malloc_print (SCM exp, SCM port, scm_print_state *pstate)
+malloc_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   scm_puts("#<malloc ", port);
   scm_intprint (SCM_CELL_WORD_1 (exp), 16, port);
diff --git a/libguile/numbers.c b/libguile/numbers.c
index 993b722ca..0beb8b2f0 100644
--- a/libguile/numbers.c
+++ b/libguile/numbers.c
@@ -2205,7 +2205,7 @@ SCM_DEFINE (scm_number_to_string, "number->string", 1, 1, 0,
    SCM_BIGDIG conditionals */
 
 int
-scm_print_real (SCM sexp, SCM port, scm_print_state *pstate)
+scm_print_real (SCM sexp, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   char num_buf[FLOBUFLEN];
   scm_lfwrite (num_buf, iflo2str (sexp, num_buf), port);
@@ -2213,7 +2213,7 @@ scm_print_real (SCM sexp, SCM port, scm_print_state *pstate)
 }
 
 int
-scm_print_complex (SCM sexp, SCM port, scm_print_state *pstate)
+scm_print_complex (SCM sexp, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   char num_buf[FLOBUFLEN];
   scm_lfwrite (num_buf, iflo2str (sexp, num_buf), port);
@@ -2221,7 +2221,7 @@ scm_print_complex (SCM sexp, SCM port, scm_print_state *pstate)
 }
 
 int
-scm_bigprint (SCM exp, SCM port, scm_print_state *pstate)
+scm_bigprint (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
 #ifdef SCM_BIGDIG
   exp = big2str (exp, (unsigned int) 10);
diff --git a/libguile/pairs.c b/libguile/pairs.c
index 812c39235..48db366b3 100644
--- a/libguile/pairs.c
+++ b/libguile/pairs.c
@@ -1,4 +1,4 @@
-/*	Copyright (C) 1995,1996, 2000 Free Software Foundation, Inc.
+/* Copyright (C) 1995,1996,2000,2001 Free Software Foundation, Inc.
  * 
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -54,6 +54,20 @@
 /* {Pairs}
  */
 
+#if (SCM_DEBUG_PAIR_ACCESSES == 1)
+
+#include "libguile/ports.h"
+#include "libguile/strings.h"
+
+void scm_error_pair_access (SCM non_pair)
+{
+  SCM message = scm_makfrom0str ("Non-pair accessed with SCM_C[AD]R: `~Sī\n");
+  scm_simple_format (scm_current_error_port (), message, SCM_LIST1 (non_pair));
+  abort ();
+}
+
+#endif
+
 SCM_DEFINE (scm_cons, "cons", 2, 0, 0,
 	    (SCM x, SCM y),
 	    "Return a newly allocated pair whose car is @var{x} and whose\n"
diff --git a/libguile/pairs.h b/libguile/pairs.h
index 96b0e47d7..17aa76cd1 100644
--- a/libguile/pairs.h
+++ b/libguile/pairs.h
@@ -1,8 +1,8 @@
 /* classes: h_files */
 
-#ifndef PAIRSH
-#define PAIRSH
-/* Copyright (C) 1995,1996,2000 Free Software Foundation, Inc.
+#ifndef SCM_PAIRS_H
+#define SCM_PAIRS_H
+/* Copyright (C) 1995,1996,2000,2001 Free Software Foundation, Inc.
  * 
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -52,14 +52,22 @@
 
 
 
+#if (SCM_DEBUG_PAIR_ACCESSES == 1)
+# include "libguile/struct.h"
+# define SCM_VALIDATE_PAIR(cell, expr) \
+    ((!SCM_ECONSP (cell) ? scm_error_pair_access (cell), 0 : 0), (expr))
+#else
+# define SCM_VALIDATE_PAIR(cell, expr) (expr)
+#endif
+
 #define SCM_NULLP(x)		(SCM_EQ_P ((x), SCM_EOL))
 #define SCM_NNULLP(x)		(!SCM_NULLP (x))
 
-#define SCM_CAR(x)		(SCM_CELL_OBJECT_0 (x))
-#define SCM_CDR(x)		(SCM_CELL_OBJECT_1 (x))
+#define SCM_CAR(x)		(SCM_VALIDATE_PAIR (x, SCM_CELL_OBJECT_0 (x)))
+#define SCM_CDR(x)		(SCM_VALIDATE_PAIR (x, SCM_CELL_OBJECT_1 (x)))
 
-#define SCM_SETCAR(x, v)	(SCM_SET_CELL_OBJECT_0 ((x), (v)))
-#define SCM_SETCDR(x, v)	(SCM_SET_CELL_OBJECT_1 ((x), (v)))
+#define SCM_SETCAR(x, v)	(SCM_VALIDATE_PAIR (x, SCM_SET_CELL_OBJECT_0 ((x), (v))))
+#define SCM_SETCDR(x, v)	(SCM_VALIDATE_PAIR (x, SCM_SET_CELL_OBJECT_1 ((x), (v))))
 
 #define SCM_CAAR(OBJ)		SCM_CAR (SCM_CAR (OBJ))
 #define SCM_CDAR(OBJ)		SCM_CDR (SCM_CAR (OBJ))
@@ -94,6 +102,9 @@
 
 
 
+#if (SCM_DEBUG_PAIR_ACCESSES == 1)
+extern void scm_error_pair_access (SCM) SCM_NORETURN;
+#endif
 extern SCM scm_cons (SCM x, SCM y);
 extern SCM scm_cons2 (SCM w, SCM x, SCM y);
 extern SCM scm_pair_p (SCM x);
@@ -101,7 +112,7 @@ extern SCM scm_set_car_x (SCM pair, SCM value);
 extern SCM scm_set_cdr_x (SCM pair, SCM value);
 extern void scm_init_pairs (void);
 
-#endif  /* PAIRSH */
+#endif  /* SCM_PAIRS_H */
 
 /*
   Local Variables:
diff --git a/libguile/ports.c b/libguile/ports.c
index 9bc8168bd..cf1ac56c7 100644
--- a/libguile/ports.c
+++ b/libguile/ports.c
@@ -108,12 +108,12 @@ scm_markstream (SCM ptr)
  */
 
 static void
-flush_port_default (SCM port)
+flush_port_default (SCM port SCM_UNUSED)
 {
 }
 
 static void
-end_input_default (SCM port, int offset)
+end_input_default (SCM port SCM_UNUSED, int offset SCM_UNUSED)
 {
 }
 
@@ -1487,7 +1487,7 @@ scm_print_port_mode (SCM exp, SCM port)
 }
 
 int
-scm_port_print (SCM exp, SCM port, scm_print_state *pstate)
+scm_port_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   char *type = SCM_PTOBNAME (SCM_PTOBNUM (exp));
   if (!type)
@@ -1514,13 +1514,15 @@ scm_ports_prehistory ()
 
 scm_bits_t scm_tc16_void_port = 0;
 
-static int fill_input_void_port (SCM port)
+static int fill_input_void_port (SCM port SCM_UNUSED)
 {
   return EOF;
 }
 
 static void
-write_void_port (SCM port, const void *data, size_t size)
+write_void_port (SCM port SCM_UNUSED,
+		 const void *data SCM_UNUSED,
+		 size_t size SCM_UNUSED)
 {
 }
 
diff --git a/libguile/ramap.c b/libguile/ramap.c
index 74e281c65..4c169753b 100644
--- a/libguile/ramap.c
+++ b/libguile/ramap.c
@@ -475,7 +475,7 @@ SCM_DEFINE (scm_array_fill_x, "array-fill!", 2, 0, 0,
 /* to be used as cproc in scm_ramapc to fill an array dimension with
    "fill". */
 int 
-scm_array_fill_int (SCM ra, SCM fill, SCM ignore)
+scm_array_fill_int (SCM ra, SCM fill, SCM ignore SCM_UNUSED)
 #define FUNC_NAME s_scm_array_fill_x
 {
   unsigned long i;
diff --git a/libguile/rdelim.c b/libguile/rdelim.c
index c029b3f8c..b8fde12e2 100644
--- a/libguile/rdelim.c
+++ b/libguile/rdelim.c
@@ -1,4 +1,4 @@
-/* 	Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
+/* Copyright (C) 1995,1996,1997,1998,1999,2000,2001 Free Software Foundation, Inc.
  * 
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
diff --git a/libguile/root.c b/libguile/root.c
index f3d6edd86..e37d77b8f 100644
--- a/libguile/root.c
+++ b/libguile/root.c
@@ -1,4 +1,4 @@
-/*	Copyright (C) 1995,1996,1997,1998, 1999, 2000 Free Software Foundation, Inc.
+/* Copyright (C) 1995,1996,1997,1998,1999,2000 Free Software Foundation, Inc.
  * 
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -92,7 +92,7 @@ root_mark (SCM root)
 
 
 static int
-root_print (SCM exp, SCM port, scm_print_state *pstate)
+root_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   scm_puts ("#<root ", port);
   scm_intprint(SCM_SEQ (SCM_ROOT_STATE (exp) -> rootcont), 16, port);
diff --git a/libguile/smob.c b/libguile/smob.c
index e2d9fcb7c..558adc979 100644
--- a/libguile/smob.c
+++ b/libguile/smob.c
@@ -84,7 +84,7 @@ scm_smob_descriptor scm_smobs[MAX_SMOB_COUNT];
    to make their links fail.  */
 
 SCM 
-scm_mark0 (SCM ptr)
+scm_mark0 (SCM ptr SCM_UNUSED)
 {
   return SCM_BOOL_F;
 }
@@ -101,7 +101,7 @@ scm_markcdr (SCM ptr)
  */
 
 size_t 
-scm_free0 (SCM ptr)
+scm_free0 (SCM ptr SCM_UNUSED)
 {
   return 0;
 }
@@ -117,7 +117,7 @@ scm_smob_free (SCM obj)
  */
 
 int
-scm_smob_print (SCM exp, SCM port, scm_print_state *pstate)
+scm_smob_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   long n = SCM_SMOBNUM (exp);
   scm_puts ("#<", port);
@@ -216,7 +216,7 @@ scm_smob_apply_1_021 (SCM smob, SCM a1)
 }
 
 static SCM
-scm_smob_apply_1_error (SCM smob, SCM a1)
+scm_smob_apply_1_error (SCM smob, SCM a1 SCM_UNUSED)
 {
   scm_wrong_num_args (smob);
 }
@@ -246,7 +246,7 @@ scm_smob_apply_2_021 (SCM smob, SCM a1, SCM a2)
 }
 
 static SCM
-scm_smob_apply_2_error (SCM smob, SCM a1, SCM a2)
+scm_smob_apply_2_error (SCM smob, SCM a1 SCM_UNUSED, SCM a2 SCM_UNUSED)
 {
   scm_wrong_num_args (smob);
 }
@@ -278,7 +278,10 @@ scm_smob_apply_3_021 (SCM smob, SCM a1, SCM a2, SCM rst)
 }
 
 static SCM
-scm_smob_apply_3_error (SCM smob, SCM a1, SCM a2, SCM rst)
+scm_smob_apply_3_error (SCM smob,
+			SCM a1 SCM_UNUSED,
+			SCM a2 SCM_UNUSED,
+			SCM rst SCM_UNUSED)
 {
   scm_wrong_num_args (smob);
 }
@@ -512,7 +515,7 @@ scm_set_smob_mfpe (long tc,
  */
 
 static int
-free_print (SCM exp, SCM port, scm_print_state *pstate)
+free_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   char buf[100];
 
diff --git a/libguile/stime.c b/libguile/stime.c
index ac99a1587..f99656da4 100644
--- a/libguile/stime.c
+++ b/libguile/stime.c
@@ -325,7 +325,7 @@ setzone (SCM zone, int pos, const char *subr)
 }
 
 static void
-restorezone (SCM zone, char **oldenv, const char *subr)
+restorezone (SCM zone, char **oldenv, const char *subr SCM_UNUSED)
 {
   if (!SCM_UNBNDP (zone))
     {
diff --git a/libguile/strings.c b/libguile/strings.c
index b87864973..a60c03ac1 100644
--- a/libguile/strings.c
+++ b/libguile/strings.c
@@ -192,7 +192,7 @@ scm_take0str (char *s)
 }
 
 SCM 
-scm_makfromstr (const char *src, size_t len, int dummy)
+scm_makfromstr (const char *src, size_t len, int dummy SCM_UNUSED)
 {
   SCM s = scm_allocate_string (len);
   char *dst = SCM_STRING_CHARS (s);
diff --git a/libguile/struct.c b/libguile/struct.c
index b13a8c1c8..dc9b7d981 100644
--- a/libguile/struct.c
+++ b/libguile/struct.c
@@ -332,7 +332,8 @@ scm_alloc_struct (int n_words, int n_extra, char *who)
 }
 
 size_t
-scm_struct_free_0 (scm_bits_t * vtable, scm_bits_t * data)
+scm_struct_free_0 (scm_bits_t * vtable SCM_UNUSED,
+		   scm_bits_t * data SCM_UNUSED)
 {
   return 0;
 }
@@ -345,7 +346,7 @@ scm_struct_free_light (scm_bits_t * vtable, scm_bits_t * data)
 }
 
 size_t
-scm_struct_free_standard (scm_bits_t * vtable, scm_bits_t * data)
+scm_struct_free_standard (scm_bits_t * vtable SCM_UNUSED, scm_bits_t * data)
 {
   size_t n = (data[scm_struct_i_n_words] + scm_struct_n_extra_words)
 	     * sizeof (scm_bits_t) + 7;
@@ -354,7 +355,7 @@ scm_struct_free_standard (scm_bits_t * vtable, scm_bits_t * data)
 }
 
 size_t
-scm_struct_free_entity (scm_bits_t * vtable, scm_bits_t * data)
+scm_struct_free_entity (scm_bits_t * vtable SCM_UNUSED, scm_bits_t * data)
 {
   size_t n = (data[scm_struct_i_n_words] + scm_struct_entity_n_extra_words)
 	     * sizeof (scm_bits_t) + 7;
@@ -363,14 +364,18 @@ scm_struct_free_entity (scm_bits_t * vtable, scm_bits_t * data)
 }
 
 static void *
-scm_struct_gc_init (void *dummy1, void *dummy2, void *dummy3)
+scm_struct_gc_init (void *dummy1 SCM_UNUSED,
+		    void *dummy2 SCM_UNUSED,
+		    void *dummy3 SCM_UNUSED)
 {
   scm_structs_to_free = SCM_EOL;
   return 0;
 }
 
 static void *
-scm_free_structs (void *dummy1, void *dummy2, void *dummy3)
+scm_free_structs (void *dummy1 SCM_UNUSED,
+		  void *dummy2 SCM_UNUSED,
+		  void *dummy3 SCM_UNUSED)
 {
   SCM newchain = scm_structs_to_free;
   do
diff --git a/libguile/symbols.c b/libguile/symbols.c
index 83cddc0da..448c9d85f 100644
--- a/libguile/symbols.c
+++ b/libguile/symbols.c
@@ -1,4 +1,4 @@
-/*	Copyright (C) 1995,1996,1997,1998, 2000, 2001 Free Software Foundation, Inc.
+/* Copyright (C) 1995,1996,1997,1998,2000,2001 Free Software Foundation, Inc.
  * 
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
diff --git a/libguile/throw.c b/libguile/throw.c
index 63af28650..765924bf6 100644
--- a/libguile/throw.c
+++ b/libguile/throw.c
@@ -84,7 +84,7 @@ static scm_bits_t tc16_jmpbuffer;
 #endif
 
 static int
-jmpbuffer_print (SCM exp, SCM port, scm_print_state *pstate)
+jmpbuffer_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   scm_puts ("#<jmpbuffer ", port);
   scm_puts (JBACTIVE(exp) ? "(active) " : "(inactive) ", port);
@@ -238,7 +238,7 @@ struct lazy_catch {
    appear in normal data structures, only in the wind list.  However,
    it might be nice for debugging someday... */
 static int
-lazy_catch_print (SCM closure, SCM port, scm_print_state *pstate)
+lazy_catch_print (SCM closure, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   struct lazy_catch *c = (struct lazy_catch *) SCM_CELL_WORD_1 (closure);
   char buf[200];
@@ -295,7 +295,7 @@ scm_internal_lazy_catch (SCM tag, scm_catch_body_t body, void *body_data, scm_ca
    scm_the_last_stack_fluid_var on error. */
 
 static SCM
-ss_handler (void *data, SCM tag, SCM throw_args)
+ss_handler (void *data SCM_UNUSED, SCM tag, SCM throw_args)
 {
   /* Save the stack */
   scm_fluid_set_x (SCM_VARIABLE_REF (scm_the_last_stack_fluid_var),
@@ -503,7 +503,7 @@ scm_handle_by_message_noexit (void *handler_data, SCM tag, SCM args)
 
 
 SCM
-scm_handle_by_throw (void *handler_data, SCM tag, SCM args)
+scm_handle_by_throw (void *handler_data SCM_UNUSED, SCM tag, SCM args)
 {
   scm_ithrow (tag, args, 1);
   return SCM_UNSPECIFIED;  /* never returns */
@@ -602,7 +602,7 @@ SCM_DEFINE (scm_throw, "throw", 1, 0, 1,
 #undef FUNC_NAME
 
 SCM
-scm_ithrow (SCM key, SCM args, int noreturn)
+scm_ithrow (SCM key, SCM args, int noreturn SCM_UNUSED)
 {
   SCM jmpbuf = SCM_UNDEFINED;
   SCM wind_goal;
diff --git a/libguile/weaks.c b/libguile/weaks.c
index 4bfe975a0..144f32cb9 100644
--- a/libguile/weaks.c
+++ b/libguile/weaks.c
@@ -217,7 +217,9 @@ SCM_DEFINE (scm_doubly_weak_hash_table_p, "doubly-weak-hash-table?", 1, 0, 0,
 #undef FUNC_NAME
 
 static void *
-scm_weak_vector_gc_init (void *dummy1, void *dummy2, void *dummy3)
+scm_weak_vector_gc_init (void *dummy1 SCM_UNUSED,
+			 void *dummy2 SCM_UNUSED,
+			 void *dummy3 SCM_UNUSED)
 {
   scm_weak_vectors = SCM_EOL;
 
@@ -225,7 +227,9 @@ scm_weak_vector_gc_init (void *dummy1, void *dummy2, void *dummy3)
 }
 
 static void *
-scm_mark_weak_vector_spines (void *dummy1, void *dummy2, void *dummy3)
+scm_mark_weak_vector_spines (void *dummy1 SCM_UNUSED,
+			     void *dummy2 SCM_UNUSED,
+			     void *dummy3 SCM_UNUSED)
 {
   SCM w;
 
@@ -262,7 +266,9 @@ scm_mark_weak_vector_spines (void *dummy1, void *dummy2, void *dummy3)
 }
 
 static void *
-scm_scan_weak_vectors (void *dummy1, void *dummy2, void *dummy3)
+scm_scan_weak_vectors (void *dummy1 SCM_UNUSED,
+		       void *dummy2 SCM_UNUSED,
+		       void *dummy3 SCM_UNUSED)
 {
   SCM *ptr, w;
   for (w = scm_weak_vectors; !SCM_NULLP (w); w = SCM_WVECT_GC_CHAIN (w))
diff --git a/srfi/ChangeLog b/srfi/ChangeLog
index dd808e359..ea5726b38 100644
--- a/srfi/ChangeLog
+++ b/srfi/ChangeLog
@@ -1,3 +1,8 @@
+2001-06-07  Dirk Herrmann  <D.Herrmann@tu-bs.de>
+
+	* srfi-14.c (charset_print): Mark unused parameters with
+	SCM_UNUSED.
+
 2001-06-07  Martin Grabmueller  <mgrabmue@cs.tu-berlin.de>
 
 	* srfi-1.scm (fold, fold-pair): Fixed a buggy call to apply.
@@ -5,7 +10,6 @@
 	retained, as required.
 	(member, assoc): Fixed wrong order of equality predicate
 	application.
-	
 
 2001-06-06  Martin Grabmueller  <mgrabmue@cs.tu-berlin.de>
 
diff --git a/srfi/srfi-14.c b/srfi/srfi-14.c
index 2cb7dc9e3..de9713bd9 100644
--- a/srfi/srfi-14.c
+++ b/srfi/srfi-14.c
@@ -1,6 +1,6 @@
 /* srfi-14.c --- SRFI-14 procedures for Guile
  *
- * 	Copyright (C) 2001 Free Software Foundation, Inc.
+ * Copyright (C) 2001 Free Software Foundation, Inc.
  * 
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as
@@ -60,7 +60,7 @@ int scm_tc16_charset = 0;
 
 /* Smob print hook for character sets.  */
 static int
-charset_print (SCM charset, SCM port, scm_print_state *pstate)
+charset_print (SCM charset, SCM port, scm_print_state *pstate SCM_UNUSED)
 {
   int i;
   int first = 1;