diff --git a/libguile/list.c b/libguile/list.c
index a343dfda5..bb38ddfc5 100644
--- a/libguile/list.c
+++ b/libguile/list.c
@@ -54,8 +54,9 @@
 #endif
 
 
+/* creating lists */
 
-
+/* SCM_P won't help us deal with varargs here.  */
 #ifdef __STDC__
 SCM
 scm_listify (SCM elt, ...)
@@ -64,7 +65,6 @@ SCM
 scm_listify (elt, va_alist)
      SCM elt;
      va_dcl
-
 #endif
 {
   va_list foo;
@@ -85,14 +85,9 @@ scm_listify (elt, va_alist)
 
 
 SCM_PROC(s_list, "list", 0, 0, 1, scm_list);
-#ifdef __STDC__
-SCM
-scm_list(SCM objs)
-#else
 SCM
 scm_list(objs)
      SCM objs;
-#endif
 {
   return objs;
 }
@@ -100,29 +95,20 @@ scm_list(objs)
 
 
 
+/* general questions about lists --- null?, list?, length, etc.  */
 
 SCM_PROC(s_null_p, "null?", 1, 0, 0, scm_null_p);
-#ifdef __STDC__
-SCM
-scm_null_p(SCM x)
-#else
 SCM
 scm_null_p(x)
      SCM x;
-#endif
 {
  return SCM_NULLP(x) ? SCM_BOOL_T : SCM_BOOL_F;
 }
 
 SCM_PROC(s_list_p, "list?", 1, 0, 0, scm_list_p);
-#ifdef __STDC__
-SCM
-scm_list_p(SCM x)
-#else
 SCM
 scm_list_p(x)
      SCM x;
-#endif
 {
   if (scm_ilength(x)<0)
     return SCM_BOOL_F;
@@ -131,41 +117,41 @@ scm_list_p(x)
 }
 
 
-#ifdef __STDC__
-long
-scm_ilength(SCM sx)
-#else
+/* Return the length of SX, or -1 if it's not a proper list.
+   This uses the "tortise and hare" algorithm to detect "infinitely
+   long" lists (i.e. lists with cycles in their cdrs), and returns -1
+   if it does find one.  */
 long
 scm_ilength(sx)
      SCM sx;
-#endif
 {
   register long i = 0;
-  register SCM x = sx;
+  register SCM tortise = sx;
+  register SCM hare = sx;
+
   do {
-    if SCM_IMP(x) return SCM_NULLP(x) ? i : -1;
-    if SCM_NCONSP(x) return -1;
-    x = SCM_CDR(x);
+    if SCM_IMP(hare) return SCM_NULLP(hare) ? i : -1;
+    if SCM_NCONSP(hare) return -1;
+    hare = SCM_CDR(hare);
     i++;
-    if SCM_IMP(x) return SCM_NULLP(x) ? i : -1;
-    if SCM_NCONSP(x) return -1;
-    x = SCM_CDR(x);
+    if SCM_IMP(hare) return SCM_NULLP(hare) ? i : -1;
+    if SCM_NCONSP(hare) return -1;
+    hare = SCM_CDR(hare);
     i++;
-    sx = SCM_CDR(sx);
+    /* For every two steps the hare takes, the tortise takes one.  */
+    tortise = SCM_CDR(tortise);
   }
-  while (x != sx);
+  while (hare != tortise);
+
+  /* If the tortise ever catches the hare, then the list must contain
+     a cycle.  */
   return -1;
 }
 
 SCM_PROC(s_list_length, "list-length", 1, 0, 0, scm_list_length);
-#ifdef __STDC__
-SCM
-scm_list_length(SCM x)
-#else
 SCM
 scm_list_length(x)
      SCM x;
-#endif
 {
   int i;
   i = scm_ilength(x);
@@ -175,16 +161,12 @@ scm_list_length(x)
 
 
 
+/* appending lists */
 
 SCM_PROC (s_list_append, "list-append", 0, 0, 1, scm_list_append);
-#ifdef __STDC__
-SCM
-scm_list_append(SCM args)
-#else
 SCM
 scm_list_append(args)
      SCM args;
-#endif
 {
   SCM res = SCM_EOL;
   SCM *lloc = &res, arg;
@@ -213,14 +195,9 @@ scm_list_append(args)
 
 
 SCM_PROC (s_list_append_x, "list-append!", 0, 0, 1, scm_list_append_x);
-#ifdef __STDC__
-SCM
-scm_list_append_x(SCM args)
-#else
 SCM
 scm_list_append_x(args)
      SCM args;
-#endif
 {
   SCM arg;
  tail:
@@ -235,18 +212,37 @@ scm_list_append_x(args)
 }
 
 
-
+SCM_PROC(s_last_pair, "last-pair", 1, 0, 0, scm_last_pair);
+SCM
+scm_last_pair(sx)
+     SCM sx;
+{
+  register SCM res = sx;
+  register SCM x;
 
+  if (SCM_NULLP (sx))
+    return SCM_EOL;
+
+  SCM_ASSERT(SCM_NIMP(res) && SCM_CONSP(res), res, SCM_ARG1, s_last_pair);
+  while (!0) {
+    x = SCM_CDR(res);
+    if (SCM_IMP(x) || SCM_NCONSP(x)) return res;
+    res = x;
+    x = SCM_CDR(res);
+    if (SCM_IMP(x) || SCM_NCONSP(x)) return res;
+    res = x;
+    sx = SCM_CDR(sx);
+    SCM_ASSERT(x != sx, sx, SCM_ARG1, s_last_pair);
+  }
+}
+
+
+/* reversing lists */
 
 SCM_PROC (s_list_reverse, "list-reverse", 1, 0, 0, scm_list_reverse);
-#ifdef __STDC__
-SCM
-scm_list_reverse(SCM lst)
-#else
 SCM
 scm_list_reverse(lst)
      SCM lst;
-#endif
 {
 	SCM res = SCM_EOL;
 	SCM p = lst;
@@ -259,15 +255,10 @@ scm_list_reverse(lst)
 }
 
 SCM_PROC (s_list_reverse_x, "list-reverse!", 1, 1, 0, scm_list_reverse_x);
-#ifdef __STDC__
-SCM
-scm_list_reverse_x (SCM lst, SCM newtail)
-#else
 SCM
 scm_list_reverse_x (lst, newtail)
      SCM lst;
      SCM newtail;
-#endif
 {
   SCM old_tail;
   if (newtail == SCM_UNDEFINED)
@@ -289,18 +280,13 @@ scm_list_reverse_x (lst, newtail)
 
 
 
-
+/* indexing lists by element number */
 
 SCM_PROC(s_list_ref, "list-ref", 2, 0, 0, scm_list_ref);
-#ifdef __STDC__
-SCM
-scm_list_ref(SCM lst, SCM k)
-#else
 SCM
 scm_list_ref(lst, k)
      SCM lst;
      SCM k;
-#endif
 {
 	register long i;
 	SCM_ASSERT(SCM_INUMP(k), k, SCM_ARG2, s_list_ref);
@@ -316,16 +302,11 @@ erout:	SCM_ASSERT(SCM_NIMP(lst) && SCM_CONSP(lst),
 }
 
 SCM_PROC(s_list_set_x, "list-set!", 3, 0, 0, scm_list_set_x);
-#ifdef __STDC__
-SCM
-scm_list_set_x(SCM lst, SCM k, SCM val)
-#else
 SCM
 scm_list_set_x(lst, k, val)
      SCM lst;
      SCM k;
      SCM val;
-#endif
 {
 	register long i;
 	SCM_ASSERT(SCM_INUMP(k), k, SCM_ARG2, s_list_set_x);
@@ -342,18 +323,30 @@ erout:	SCM_ASSERT(SCM_NIMP(lst) && SCM_CONSP(lst),
 }
 
 
+SCM_PROC(s_list_cdr_ref, "list-cdr-ref", 2, 0, 0, scm_list_tail);
+SCM_PROC(s_list_tail, "list-tail", 2, 0, 0, scm_list_tail);
+SCM
+scm_list_tail(lst, k)
+     SCM lst;
+     SCM k;
+{
+  register long i;
+  SCM_ASSERT(SCM_INUMP(k), k, SCM_ARG2, s_list_tail);
+  i = SCM_INUM(k);
+  while (i-- > 0) {
+    SCM_ASSERT(SCM_NIMP(lst) && SCM_CONSP(lst), lst, SCM_ARG1, s_list_tail);
+    lst = SCM_CDR(lst);
+  }
+  return lst;
+}
+
 
 SCM_PROC(s_list_cdr_set_x, "list-cdr-set!", 3, 0, 0, scm_list_cdr_set_x);
-#ifdef __STDC__
-SCM
-scm_list_cdr_set_x(SCM lst, SCM k, SCM val)
-#else
 SCM
 scm_list_cdr_set_x(lst, k, val)
      SCM lst;
      SCM k;
      SCM val;
-#endif
 {
 	register long i;
 	SCM_ASSERT(SCM_INUMP(k), k, SCM_ARG2, s_list_cdr_set_x);
@@ -371,71 +364,13 @@ erout:	SCM_ASSERT(SCM_NIMP(lst) && SCM_CONSP(lst),
 
 
 
-
-
-
-SCM_PROC(s_last_pair, "last-pair", 1, 0, 0, scm_last_pair);
-#ifdef __STDC__
-SCM
-scm_last_pair(SCM sx)
-#else
-SCM
-scm_last_pair(sx)
-     SCM sx;
-#endif
-{
-  register SCM res = sx;
-  register SCM x;
-
-  if (SCM_NULLP (sx))
-    return SCM_EOL;
-
-  SCM_ASSERT(SCM_NIMP(res) && SCM_CONSP(res), res, SCM_ARG1, s_last_pair);
-  while (!0) {
-    x = SCM_CDR(res);
-    if (SCM_IMP(x) || SCM_NCONSP(x)) return res;
-    res = x;
-    x = SCM_CDR(res);
-    if (SCM_IMP(x) || SCM_NCONSP(x)) return res;
-    res = x;
-    sx = SCM_CDR(sx);
-    SCM_ASSERT(x != sx, sx, SCM_ARG1, s_last_pair);
-  }
-}
-
-SCM_PROC(s_list_cdr_ref, "list-cdr-ref", 2, 0, 0, scm_list_tail);
-SCM_PROC(s_list_tail, "list-tail", 2, 0, 0, scm_list_tail);
-#ifdef __STDC__
-SCM
-scm_list_tail(SCM lst, SCM k)
-#else
-SCM
-scm_list_tail(lst, k)
-     SCM lst;
-     SCM k;
-#endif
-{
-  register long i;
-  SCM_ASSERT(SCM_INUMP(k), k, SCM_ARG2, s_list_tail);
-  i = SCM_INUM(k);
-  while (i-- > 0) {
-    SCM_ASSERT(SCM_NIMP(lst) && SCM_CONSP(lst), lst, SCM_ARG1, s_list_tail);
-    lst = SCM_CDR(lst);
-  }
-  return lst;
-}
-
+/* copying lists, perhaps partially */
 
 SCM_PROC(s_list_head, "list-head", 2, 0, 0, scm_list_head);
-#ifdef __STDC__
-SCM
-scm_list_head(SCM lst, SCM k)
-#else
 SCM
 scm_list_head(lst, k)
      SCM lst;
      SCM k;
-#endif
 {
   SCM answer;
   SCM * pos;
@@ -456,33 +391,50 @@ scm_list_head(lst, k)
 }
 
 
-
+SCM_PROC (s_list_copy, "list-copy", 1, 0, 0, scm_list_copy);
+SCM 
+scm_list_copy (lst)
+     SCM lst;
+{
+  SCM newlst;
+  SCM * fill_here;
+  SCM from_here;
+
+  newlst = SCM_EOL;
+  fill_here = &newlst;
+  from_here = lst;
+
+  while (SCM_NIMP (from_here) && SCM_CONSP (from_here))
+    {
+      SCM c;
+      c = scm_cons (SCM_CAR (from_here), SCM_CDR (from_here));
+      *fill_here = c;
+      fill_here = &SCM_CDR (c);
+      from_here = SCM_CDR (from_here);
+    }
+  return newlst;
+}
+
+
+/* membership tests (memq, memv, etc.) */ 
+
+static void sloppy_mem_check SCM_P ((SCM obj, char * where, char * why));
 
-#ifdef __STDC__
-static void
-sloppy_mem_check (SCM obj, char * where, char * why)
-#else
 static void
 sloppy_mem_check (obj, where, why)
      SCM obj;
      char * where;
      char * why;
-#endif
 {
   SCM_ASSERT ((scm_ilength (obj) >= 0), obj, where, why);
 }
 
 
 SCM_PROC (s_sloppy_memq, "sloppy-memq", 2, 0, 0, scm_sloppy_memq);
-#ifdef __STDC__
-SCM
-scm_sloppy_memq(SCM x, SCM lst)
-#else
 SCM
 scm_sloppy_memq(x, lst)
      SCM x;
      SCM lst;
-#endif
 {
   for(;  SCM_NIMP(lst) && SCM_CONSP (lst);  lst = SCM_CDR(lst))
     {
@@ -494,15 +446,10 @@ scm_sloppy_memq(x, lst)
 
 
 SCM_PROC (s_sloppy_memv, "sloppy-memv", 2, 0, 0, scm_sloppy_memv);
-#ifdef __STDC__
-SCM
-scm_sloppy_memv(SCM x, SCM lst)
-#else
 SCM
 scm_sloppy_memv(x, lst)
      SCM x;
      SCM lst;
-#endif
 {
   for(;  SCM_NIMP(lst) && SCM_CONSP (lst);  lst = SCM_CDR(lst))
     {
@@ -514,15 +461,10 @@ scm_sloppy_memv(x, lst)
 
 
 SCM_PROC (s_sloppy_member, "sloppy-member", 2, 0, 0, scm_sloppy_member);
-#ifdef __STDC__
-SCM
-scm_sloppy_member (SCM x, SCM lst)
-#else
 SCM
 scm_sloppy_member (x, lst)
      SCM x;
      SCM lst;
-#endif
 {
   for(;  SCM_NIMP(lst) && SCM_CONSP (lst);  lst = SCM_CDR(lst))
     {
@@ -535,72 +477,53 @@ scm_sloppy_member (x, lst)
 
 
 SCM_PROC(s_memq, "memq", 2, 0, 0, scm_memq);
-#ifdef __STDC__
-SCM
-scm_memq(SCM x, SCM lst)
-#else
 SCM
 scm_memq(x, lst)
      SCM x;
      SCM lst;
-#endif
 {
   SCM answer;
   answer = scm_sloppy_memq (x, lst);
   sloppy_mem_check (answer, (char *)SCM_ARG2, s_memq);
-  return answer;
+  return (answer == SCM_EOL) ? SCM_BOOL_F : answer;
 }
 
 
 
 SCM_PROC(s_memv, "memv", 2, 0, 0, scm_memv);
-#ifdef __STDC__
-SCM
-scm_memv(SCM x, SCM lst)
-#else
 SCM
 scm_memv(x, lst)
      SCM x;
      SCM lst;
-#endif
 {
   SCM answer;
   answer = scm_sloppy_memv (x, lst);
   sloppy_mem_check (answer, (char *)SCM_ARG2, s_memv);
-  return answer;
+  return (answer == SCM_EOL) ? SCM_BOOL_F : answer;
 }
 
 
 SCM_PROC(s_member, "member", 2, 0, 0, scm_member);
-#ifdef __STDC__
-SCM
-scm_member(SCM x, SCM lst)
-#else
 SCM
 scm_member(x, lst)
      SCM x;
      SCM lst;
-#endif
 {
   SCM answer;
   answer = scm_sloppy_member (x, lst);
   sloppy_mem_check (answer, (char *)SCM_ARG2, s_member);
-  return answer;
+  return (answer == SCM_EOL) ? SCM_BOOL_F : answer;
 }
 
 
 
+/* deleting elements from a list (delq, etc.) */
 
 SCM_PROC(s_delq_x, "delq!", 2, 0, 0, scm_delq_x);
-#ifdef __STDC__
-SCM
-scm_delq_x (SCM item, SCM lst)
-#else
 SCM
 scm_delq_x (item, lst)
      SCM item;
      SCM lst;
-#endif
 {
   SCM start;
 
@@ -626,15 +549,10 @@ scm_delq_x (item, lst)
 
 
 SCM_PROC(s_delv_x, "delv!", 2, 0, 0, scm_delv_x);
-#ifdef __STDC__
-SCM
-scm_delv_x (SCM item, SCM lst)
-#else
 SCM
 scm_delv_x (item, lst)
      SCM item;
      SCM lst;
-#endif
 {
   SCM start;
 
@@ -661,15 +579,10 @@ scm_delv_x (item, lst)
 
 
 SCM_PROC(s_delete_x, "delete!", 2, 0, 0, scm_delete_x);
-#ifdef __STDC__
-SCM
-scm_delete_x (SCM item, SCM lst)
-#else
 SCM
 scm_delete_x (item, lst)
      SCM item;
      SCM lst;
-#endif
 {
   SCM start;
 
@@ -696,47 +609,12 @@ scm_delete_x (item, lst)
 
 
 
-SCM_PROC (s_list_copy, "list-copy", 1, 0, 0, scm_list_copy);
-#ifdef __STDC__
-SCM 
-scm_list_copy (SCM lst)
-#else
-SCM 
-scm_list_copy (lst)
-     SCM lst;
-#endif
-{
-  SCM newlst;
-  SCM * fill_here;
-  SCM from_here;
-
-  newlst = SCM_EOL;
-  fill_here = &newlst;
-  from_here = lst;
-
-  while (SCM_NIMP (from_here) && SCM_CONSP (from_here))
-    {
-      SCM c;
-      c = scm_cons (SCM_CAR (from_here), SCM_CDR (from_here));
-      *fill_here = c;
-      fill_here = &SCM_CDR (c);
-      from_here = SCM_CDR (from_here);
-    }
-  return newlst;
-}
-
-
 
 SCM_PROC (s_delq, "delq", 2, 0, 0, scm_delq);
-#ifdef __STDC__
-SCM
-scm_delq (SCM item, SCM lst)
-#else
 SCM
 scm_delq (item, lst)
      SCM item;
      SCM lst;
-#endif
 {
   SCM copy;
 
@@ -745,15 +623,10 @@ scm_delq (item, lst)
 }
 
 SCM_PROC (s_delv, "delv", 2, 0, 0, scm_delv);
-#ifdef __STDC__
-SCM
-scm_delv (SCM item, SCM lst)
-#else
 SCM
 scm_delv (item, lst)
      SCM item;
      SCM lst;
-#endif
 {
   SCM copy;
 
@@ -762,15 +635,10 @@ scm_delv (item, lst)
 }
 
 SCM_PROC (s_delete, "delete", 2, 0, 0, scm_delete);
-#ifdef __STDC__
-SCM
-scm_delete (SCM item, SCM lst)
-#else
 SCM
 scm_delete (item, lst)
      SCM item;
      SCM lst;
-#endif
 {
   SCM copy;
 
@@ -780,15 +648,8 @@ scm_delete (item, lst)
 
 
 
-
-#ifdef __STDC__
-void
-scm_init_list (void)
-#else
 void
 scm_init_list ()
-#endif
 {
 #include "list.x"
 }
-
diff --git a/libguile/list.h b/libguile/list.h
index a969b46fa..82d560673 100644
--- a/libguile/list.h
+++ b/libguile/list.h
@@ -47,82 +47,36 @@
 #include "libguile/__scm.h"
 
 
-
-
-
-
-#ifdef __STDC__
-extern SCM scm_list_head (SCM lst, SCM k);
-extern SCM scm_listify (SCM elt, ...);
-extern SCM scm_list(SCM objs);
-extern SCM scm_null_p(SCM x);
-extern SCM scm_list_p(SCM x);
-extern long scm_ilength(SCM sx);
-extern SCM scm_list_length(SCM x);
-extern SCM scm_list_append(SCM args);
-extern SCM scm_list_append_x(SCM args);
-extern SCM scm_list_reverse(SCM lst);
-extern SCM scm_list_reverse_x (SCM lst, SCM newtail);
-extern SCM scm_list_ref(SCM lst, SCM k);
-extern SCM scm_list_set_x(SCM lst, SCM k, SCM val);
-extern SCM scm_list_cdr_ref(SCM lst, SCM k);
-extern SCM scm_list_cdr_set_x(SCM lst, SCM k, SCM val);
-extern SCM scm_last_pair(SCM sx);
-extern SCM scm_list_tail(SCM lst, SCM k);
-extern SCM scm_sloppy_memq(SCM x, SCM lst);
-extern SCM scm_sloppy_memv(SCM x, SCM lst);
-extern SCM scm_sloppy_member (SCM x, SCM lst);
-extern SCM scm_memq(SCM x, SCM lst);
-extern SCM scm_memv(SCM x, SCM lst);
-extern SCM scm_member(SCM x, SCM lst);
-extern SCM scm_delq_x (SCM item, SCM lst);
-extern SCM scm_delv_x (SCM item, SCM lst);
-extern SCM scm_delete_x (SCM item, SCM lst);
-extern SCM scm_list_copy (SCM lst);
-extern SCM scm_delq (SCM item, SCM lst);
-extern SCM scm_delv (SCM item, SCM lst);
-extern SCM scm_delete (SCM item, SCM lst);
-extern void scm_init_list (void);
-
-#else /* STDC */
-extern SCM scm_list_head ();
-extern SCM scm_listify ();
-extern SCM scm_list();
-extern SCM scm_null_p();
-extern SCM scm_list_p();
-extern long scm_ilength();
-extern SCM scm_list_length();
-extern SCM scm_list_append();
-extern SCM scm_list_append_x();
-extern SCM scm_list_reverse();
-extern SCM scm_list_reverse_x ();
-extern SCM scm_list_ref();
-extern SCM scm_list_set_x();
-extern SCM scm_list_cdr_ref();
-extern SCM scm_list_cdr_set_x();
-extern SCM scm_last_pair();
-extern SCM scm_list_tail();
-extern SCM scm_sloppy_memq();
-extern SCM scm_sloppy_memv();
-extern SCM scm_sloppy_member ();
-extern SCM scm_memq();
-extern SCM scm_memv();
-extern SCM scm_member();
-extern SCM scm_delq_x ();
-extern SCM scm_delv_x ();
-extern SCM scm_delete_x ();
-extern SCM scm_list_copy ();
-extern SCM scm_delq ();
-extern SCM scm_delv ();
-extern SCM scm_delete ();
-extern void scm_init_list ();
-
-#endif /* STDC */
-
-
-
-
-
-
+extern SCM scm_list_head SCM_P ((SCM lst, SCM k));
+extern SCM scm_listify SCM_P ((SCM elt, ...));
+extern SCM scm_list SCM_P ((SCM objs));
+extern SCM scm_null_p SCM_P ((SCM x));
+extern SCM scm_list_p SCM_P ((SCM x));
+extern long scm_ilength SCM_P ((SCM sx));
+extern SCM scm_list_length SCM_P ((SCM x));
+extern SCM scm_list_append SCM_P ((SCM args));
+extern SCM scm_list_append_x SCM_P ((SCM args));
+extern SCM scm_list_reverse SCM_P ((SCM lst));
+extern SCM scm_list_reverse_x SCM_P ((SCM lst, SCM newtail));
+extern SCM scm_list_ref SCM_P ((SCM lst, SCM k));
+extern SCM scm_list_set_x SCM_P ((SCM lst, SCM k, SCM val));
+extern SCM scm_list_cdr_ref SCM_P ((SCM lst, SCM k));
+extern SCM scm_list_cdr_set_x SCM_P ((SCM lst, SCM k, SCM val));
+extern SCM scm_last_pair SCM_P ((SCM sx));
+extern SCM scm_list_tail SCM_P ((SCM lst, SCM k));
+extern SCM scm_sloppy_memq SCM_P ((SCM x, SCM lst));
+extern SCM scm_sloppy_memv SCM_P ((SCM x, SCM lst));
+extern SCM scm_sloppy_member SCM_P ((SCM x, SCM lst));
+extern SCM scm_memq SCM_P ((SCM x, SCM lst));
+extern SCM scm_memv SCM_P ((SCM x, SCM lst));
+extern SCM scm_member SCM_P ((SCM x, SCM lst));
+extern SCM scm_delq_x SCM_P ((SCM item, SCM lst));
+extern SCM scm_delv_x SCM_P ((SCM item, SCM lst));
+extern SCM scm_delete_x SCM_P ((SCM item, SCM lst));
+extern SCM scm_list_copy SCM_P ((SCM lst));
+extern SCM scm_delq SCM_P ((SCM item, SCM lst));
+extern SCM scm_delv SCM_P ((SCM item, SCM lst));
+extern SCM scm_delete SCM_P ((SCM item, SCM lst));
+extern void scm_init_list SCM_P ((void));
 
 #endif  /* LISTH */