* Makefile (OBJS): New object file, combi.o.

* dep.mk: Updated.

* eval.c: Removed combination and permutation functions; they
now reside in combi.c.
(generate): Changed from static to external linkage.

* eval.h (generate): Declared.

* combi.c: New file.

* combi.h: New file.

* txr.vim: Regenerated.

8 files changed, 703 insertions, 614 deletions

diff --git a/ChangeLog b/ChangeLog
index 48d91ce2..b5524435 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,23 @@
 2014-02-10  Kaz Kylheku  <kaz@kylheku.com>
 
+	* Makefile (OBJS): New object file, combi.o.
+
+	* dep.mk: Updated.
+
+	* eval.c: Removed combination and permutation functions; they
+	now reside in combi.c.
+	(generate): Changed from static to external linkage.
+
+	* eval.h (generate): Declared.
+
+	* combi.c: New file.
+
+	* combi.h: New file.
+
+	* txr.vim: Regenerated.
+
+2014-02-10  Kaz Kylheku  <kaz@kylheku.com>
+
 	* eval.c (rcomb_gen_fun_common): Streamlined implementation.
 	Got rid of stack that is consed up on each call.
 
diff --git a/Makefile b/Makefile
index 99d0b66f..9fd20178 100644
--- a/Makefile
+++ b/Makefile
@@ -39,7 +39,7 @@ endif
 
 # TXR objects
 OBJS := txr.o lex.yy.o y.tab.o match.o lib.o regex.o gc.o unwind.o stream.o
-OBJS += arith.o hash.o utf8.o filter.o eval.o rand.o
+OBJS += arith.o hash.o utf8.o filter.o eval.o rand.o combi.o
 OBJS-$(debug_support) += debug.o
 OBJS-$(have_syslog) += syslog.o
 OBJS-$(have_posix_sigs) += signal.o
diff --git a/combi.c b/combi.c
new file mode 100644
index 00000000..2af2a051
--- /dev/null
+++ b/combi.c
@@ -0,0 +1,581 @@
+/* Copyright 2010-2014
+ * Kaz Kylheku <kaz@kylheku.com>
+ * Vancouver, Canada
+ * All rights reserved.
+ *
+ * BSD License:
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *   1. Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *   2. Redistributions in binary form must reproduce the above copyright
+ *      notice, this list of conditions and the following disclaimer in
+ *      the documentation and/or other materials provided with the
+ *      distribution.
+ *   3. The name of the author may not be used to endorse or promote
+ *      products derived from this software without specific prior
+ *      written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+#include <wctype.h>
+#include <setjmp.h>
+#include <wchar.h>
+#include <signal.h>
+#include "config.h"
+#include "lib.h"
+#include "signal.h"
+#include "unwind.h"
+#include "eval.h"
+#include "combi.h"
+
+static val perm_while_fun(val state)
+{
+  val p = vecref(state, zero);
+  cnum k = c_num(vecref(state, one));
+  val c = vecref(state, two);
+  cnum n = c_num(length(p));
+  cnum i, j; 
+
+  for (i = k - 1, j = n - k + 1; i >= 0; i--, j++) {
+    cnum ci = c_num(c->v.vec[i]) + 1;
+
+    if (ci >= j) {
+      if (i == 0)
+        return nil;
+      c->v.vec[i] = zero;
+    } else {
+      c->v.vec[i] = num_fast(ci);
+      break;
+    }
+  }
+
+  return t;
+}
+
+static cnum perm_index(cnum n, val b)
+{
+  cnum i, j;
+
+  for (i = 0, j = 0; i < n; i++, j++) {
+    while (b->v.vec[j])
+      j++;
+  }
+
+  while (b->v.vec[j])
+    j++;
+
+  return j;
+}
+
+static void perm_gen_fun_common(val state, val out,
+                                void (*fill)(val out, cnum i, val v))
+{
+  val p = vecref(state, zero);
+  val kk = vecref(state, one);
+  val c = vecref(state, two);
+  val nn = length(p);
+  val b = vector(nn, nil);
+  cnum k = c_num(kk);
+  cnum i; 
+
+  for (i = 0; i < k; i++) {
+    cnum ci = c_num(c->v.vec[i]);
+    cnum j = perm_index(ci, b);
+    fill(out, i, p->v.vec[j]);
+    b->v.vec[j] = t;
+  }
+}
+
+static val perm_init_common(val p, val k_null)
+{
+  uses_or2;
+  val n = length(p);
+  val k = or2(k_null, n);
+
+  if (gt(k, n)) {
+    return nil;
+  } else {
+    val state = vector(three, nil);
+    val c = vector(k, zero);
+    *vecref_l(state, zero) = p;
+    *vecref_l(state, one) = k;
+    *vecref_l(state, two) = c;
+    *vecref_l(c, negone) = negone;
+    return state;
+  }
+}
+
+static void perm_vec_gen_fill(val out, cnum i, val v)
+{
+  out->v.vec[i] = v;
+}
+
+static val perm_vec_gen_fun(val state)
+{
+  val kk = vecref(state, one);
+  val out = vector(kk, nil);
+  perm_gen_fun_common(state, out, perm_vec_gen_fill);
+  return out;
+}
+
+static val perm_vec(val p, val k)
+{
+  k = default_arg(k, length_vec(p));
+
+  if (k == zero) {
+    return cons(vector(zero, nil), nil);
+  } else {
+    val state = perm_init_common(p, k);
+    if (!state)
+      return nil;
+    return generate(func_f0(state, perm_while_fun),
+                    func_f0(state, perm_vec_gen_fun));
+  }
+}
+
+static void perm_list_gen_fill(val out, cnum i, val v)
+{
+  val tail = cdr(out);
+  val nc = cons(v, nil);
+  if (tail)
+    rplacd(tail, nc);
+  else
+    rplaca(out, nc);
+  rplacd(out, nc);
+}
+
+static val perm_list_gen_fun(val state)
+{
+  val out = cons(nil, nil);
+  perm_gen_fun_common(state, out, perm_list_gen_fill);
+  return car(out);
+}
+
+static val perm_list(val p, val k)
+{
+  if (k == zero || (!k && !p)) {
+    return cons(nil, nil);
+  } else {
+    val state = perm_init_common(vector_list(p), k);
+    if (!state)
+      return nil;
+    return generate(func_f0(state, perm_while_fun),
+                    func_f0(state, perm_list_gen_fun));
+  }
+}
+
+static void perm_str_gen_fill(val out, cnum i, val v)
+{
+  out->st.str[i] = c_chr(v);
+}
+
+static val perm_str_gen_fun(val state)
+{
+  val kk = vecref(state, one);
+  val out = mkustring(kk);
+  perm_gen_fun_common(state, out, perm_str_gen_fill);
+  out->st.str[c_num(kk)] = 0;
+  return out;
+}
+
+static val perm_str(val p, val k)
+{
+  k = default_arg(k, length_str(p));
+
+  if (k == zero) {
+    return cons(string(L""), nil);
+  } else {
+    val state = perm_init_common(vector_list(list_str(p)), k);
+    if (!state)
+      return nil;
+    return generate(func_f0(state, perm_while_fun),
+                    func_f0(state, perm_str_gen_fun));
+  }
+}
+
+val perm(val seq, val k)
+{
+  if (null_or_missing_p(k)) {
+    k = nil;
+  } else {
+    if (!integerp(k))
+      type_mismatch(lit("perm: ~s is not an integer"), k, nao);
+
+    if (lt(k, zero))
+      uw_throwf(numeric_error_s, lit("perm: ~s is not a positive integer"),
+                k, nao);
+  }
+
+  switch (type(seq)) {
+  case CONS:
+  case LCONS:
+  case NIL:
+    return perm_list(seq, k);
+  case VEC:
+    return perm_vec(seq, k);
+  case STR:
+  case LSTR:
+  case LIT:
+    return perm_str(seq, k);
+  default:
+    type_mismatch(lit("perm: ~s is not a sequence"), seq, nao);
+  }
+}
+
+static val rperm_while_fun(val env)
+{
+  val vec = cdr(env);
+  return consp(vecref(vec, zero));
+}
+
+static val rperm_gen_fun(val env)
+{
+  cons_bind (list, vec, env);
+  list_collect_decl(out, ptail);
+  cnum i;
+  cnum len = c_num(length_vec(vec));
+
+  for (i = 0; i < len; i++)
+    list_collect(ptail, car(vec->v.vec[i]));
+
+  for (i = len-1; i >= 0; i--) {
+    pop(&vec->v.vec[i]);
+    if (atom(vec->v.vec[i]) && i > 0)
+      vec->v.vec[i] = list;
+    else
+      break;
+  }
+
+  return out;
+}
+
+static val rperm_list(val list, val k)
+{
+  val vec = vector(k, list);
+  val env = cons(list, vec);
+  return generate(func_f0(env, rperm_while_fun),
+                  func_f0(env, rperm_gen_fun));
+}
+
+static val rperm_vec_gen_fun(val env)
+{
+  val list = rperm_gen_fun(env);
+  return vector_list(list);
+}
+
+static val rperm_vec(val ve, val k)
+{
+  val list = list_vector(ve);
+  val vec = vector(k, list);
+  val env = cons(list, vec);
+  return generate(func_f0(env, rperm_while_fun),
+                  func_f0(env, rperm_vec_gen_fun));
+}
+
+static val rperm_str_gen_fun(val env)
+{
+  val list = rperm_gen_fun(env);
+  return cat_str(list, nil);
+}
+
+static val rperm_str(val str, val k)
+{
+  val list = list_str(str);
+  val vec = vector(k, list);
+  val env = cons(list, vec);
+  return generate(func_f0(env, rperm_while_fun),
+                  func_f0(env, rperm_str_gen_fun));
+}
+
+val rperm(val seq, val k)
+{
+  if (!integerp(k))
+    type_mismatch(lit("rperm: ~s is not an integer"), k, nao);
+
+  if (lt(k, zero))
+    uw_throwf(numeric_error_s, lit("rperm: ~s is not a positive integer"),
+              k, nao);
+
+  switch (type(seq)) {
+  case NIL:
+    if (zerop(k))
+      return cons(nil, nil);
+    return nil;
+  case CONS:
+  case LCONS:
+    if (zerop(k))
+      return cons(nil, nil);
+    return rperm_list(seq, k);
+  case VEC:
+    if (zerop(k))
+      return cons(vector(zero, nil), nil);
+    return rperm_vec(seq, k);
+  case STR:
+  case LSTR:
+  case LIT:
+    if (zerop(k))
+      return cons(string(L""), nil);
+    return rperm_str(seq, k);
+  default:
+    type_mismatch(lit("rperm: ~s is not a sequence"), seq, nao);
+  }
+}
+
+
+static val k_conses(val list, val k)
+{
+  val iter = list, i = k;
+  list_collect_decl (out, ptail);
+
+  for (; consp(iter) && gt(i, zero); iter = cdr(iter), i = minus(i, one))
+    ptail = list_collect(ptail, iter);
+
+  return (i != zero) ? nil : out;
+}
+
+static val comb_while_fun(val state)
+{
+  return car(state);
+}
+
+static void comb_gen_fun_common(val state)
+{
+  val iter;
+  val prev = nil;
+
+  for (iter = state; consp(iter); iter = cdr(iter)) {
+    val curr = first(iter);
+    val curr_rest = rest(curr);
+    if (curr_rest != prev && consp(curr_rest)) {
+      *car_l(iter) = curr_rest;
+      return;
+    } else if (rest(iter)) {
+      val next = second(iter);
+      val next_rest = rest(next);
+      val next_rest_rest = rest(next_rest);
+      prev = curr;
+      if (next_rest != curr && consp(next_rest_rest))
+        prev = *car_l(iter) = next_rest_rest;
+    } 
+  }
+
+  *car_l(state) = nil;
+}
+
+static val comb_list_gen_fun(val state)
+{
+  val out = nreverse(mapcar(car_f, state));
+  comb_gen_fun_common(state);
+  return out;
+}
+
+static val comb_list(val list, val k)
+{
+  val state = nreverse(k_conses(list, k));
+  return state ? generate(func_f0(state, comb_while_fun),
+                          func_f0(state, comb_list_gen_fun))
+               : nil;
+}
+
+static val comb_vec_gen_fun(val state)
+{
+  val nn = length_list(state);
+  cnum i, n = c_num(nn);
+  val iter, out = vector(nn, nil);
+
+  for (iter = state, i = n - 1; i >= 0; iter = cdr(iter), i--)
+    out->v.vec[i] = car(car(iter));
+
+  comb_gen_fun_common(state);
+  return out;
+}
+
+static val comb_vec(val vec, val k)
+{
+  val state = nreverse(k_conses(list_vector(vec), k));
+  return generate(func_f0(state, comb_while_fun),
+                  func_f0(state, comb_vec_gen_fun));
+}
+
+static val comb_str_gen_fun(val state)
+{
+  val nn = length_list(state);
+  cnum i, n = c_num(nn);
+  val iter, out = mkustring(nn);
+
+  out->st.str[n] = 0;
+
+  for (iter = state, i = n - 1; i >= 0; iter = cdr(iter), i--)
+    out->st.str[i] = c_chr(car(car(iter)));
+
+  comb_gen_fun_common(state);
+  return out;
+}
+
+static val comb_str(val str, val k)
+{
+  val state = nreverse(k_conses(list_str(str), k));
+  return generate(func_f0(state, comb_while_fun),
+                  func_f0(state, comb_str_gen_fun));
+}
+
+val comb(val seq, val k)
+{
+  if (!integerp(k))
+    type_mismatch(lit("comb: ~s is not an integer"), k, nao);
+
+  if (lt(k, zero))
+    uw_throwf(numeric_error_s, lit("comb: ~s is not a positive integer"),
+              k, nao);
+
+  switch (type(seq)) {
+  case CONS:
+  case LCONS:
+  case NIL:
+    if (k == zero)
+      return cons(nil, nil);
+    return comb_list(seq, k);
+  case VEC:
+    if (k == zero)
+      return cons(vector(zero, nil), nil);
+    if (gt(k, length(seq)))
+      return nil;
+    return comb_vec(seq, k);
+  case STR:
+  case LSTR:
+  case LIT:
+    if (k == zero)
+      return cons(string(L""), nil);
+    if (gt(k, length(seq)))
+      return nil;
+    return comb_str(seq, k);
+  default:
+    type_mismatch(lit("comb: ~s is not a sequence"), seq, nao);
+  }
+}
+
+static val rcomb_while_fun(val state)
+{
+  return car(state);
+}
+
+static void rcomb_gen_fun_common(val state)
+{
+  val iter;
+  val next;
+
+  for (iter = state, next = cdr(state);
+       consp(iter);
+       iter = next, next = cdr(iter))
+  {
+    val curr = first(iter);
+    val curr_rest = rest(curr);
+
+    if (consp(curr_rest)) {
+      val jter;
+      for (jter = state; jter != next; jter = cdr(jter))
+        *car_l(jter) = curr_rest;
+      return;
+    } else if (next) {
+      val next = second(iter);
+      if (curr != next)
+        *car_l(iter) = rest(next);
+    } 
+  }
+
+  *car_l(state) = nil;
+}
+
+static val rcomb_list_gen_fun(val state)
+{
+  val out = nreverse(mapcar(car_f, state));
+  rcomb_gen_fun_common(state);
+  return out;
+}
+
+static val rcomb_list(val list, val k)
+{
+  val state = nreverse(list_vector(vector(k, list)));
+  return generate(func_f0(state, rcomb_while_fun),
+                  func_f0(state, rcomb_list_gen_fun));
+}
+
+static val rcomb_vec_gen_fun(val state)
+{
+  val nn = length_list(state);
+  cnum i, n = c_num(nn);
+  val iter, out = vector(nn, nil);
+
+  for (iter = state, i = n - 1; i >= 0; iter = cdr(iter), i--)
+    out->v.vec[i] = car(car(iter));
+
+  rcomb_gen_fun_common(state);
+  return out;
+}
+
+static val rcomb_vec(val vec, val k)
+{
+  val state = nreverse(list_vector(vector(k, list_vector(vec))));
+  return generate(func_f0(state, rcomb_while_fun),
+                  func_f0(state, rcomb_vec_gen_fun));
+}
+
+static val rcomb_str_gen_fun(val state)
+{
+  val nn = length_list(state);
+  cnum i, n = c_num(nn);
+  val iter, out = mkustring(nn);
+
+  out->st.str[n] = 0;
+
+  for (iter = state, i = n - 1; i >= 0; iter = cdr(iter), i--)
+    out->st.str[i] = c_chr(car(car(iter)));
+
+  rcomb_gen_fun_common(state);
+  return out;
+}
+
+static val rcomb_str(val str, val k)
+{
+  val state = nreverse(list_vector(vector(k, list_str(str))));
+  return generate(func_f0(state, rcomb_while_fun),
+                  func_f0(state, rcomb_str_gen_fun));
+}
+
+val rcomb(val seq, val k)
+{
+  if (!integerp(k))
+    type_mismatch(lit("rcomb: ~s is not an integer"), k, nao);
+
+  if (lt(k, zero))
+    uw_throwf(numeric_error_s, lit("rcomb: ~s is not a positive integer"),
+              k, nao);
+
+  switch (type(seq)) {
+  case CONS:
+  case LCONS:
+  case NIL:
+    if (k == zero)
+      return cons(nil, nil);
+    return rcomb_list(seq, k);
+  case VEC:
+    if (k == zero)
+      return cons(vector(zero, nil), nil);
+    return rcomb_vec(seq, k);
+  case STR:
+  case LSTR:
+  case LIT:
+    if (k == zero)
+      return cons(string(L""), nil);
+    return rcomb_str(seq, k);
+  default:
+    type_mismatch(lit("rcomb: ~s is not a sequence"), seq, nao);
+  }
+}
diff --git a/combi.h b/combi.h
new file mode 100644
index 00000000..51c41f94
--- /dev/null
+++ b/combi.h
@@ -0,0 +1,30 @@
+/* Copyright 2012-2014
+ * Kaz Kylheku <kaz@kylheku.com>
+ * Vancouver, Canada
+ * All rights reserved.
+ *
+ * BSD License:
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *   1. Redistributions of source code must retain the above copyright
+ *      notice, this list of conditions and the following disclaimer.
+ *   2. Redistributions in binary form must reproduce the above copyright
+ *      notice, this list of conditions and the following disclaimer in
+ *      the documentation and/or other materials provided with the
+ *      distribution.
+ *   3. The name of the author may not be used to endorse or promote
+ *      products derived from this software without specific prior
+ *      written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+val perm(val seq, val k);
+val rperm(val seq, val k);
+val comb(val seq, val k);
+val rcomb(val seq, val k);
diff --git a/dep.mk b/dep.mk
index 27bc8311..7fe347af 100644
--- a/dep.mk
+++ b/dep.mk
@@ -11,8 +11,9 @@
 ./hash.o: config.h $(top_srcdir)/./lib.h $(top_srcdir)/./gc.h $(top_srcdir)/./signal.h $(top_srcdir)/./unwind.h $(top_srcdir)/./stream.h $(top_srcdir)/./hash.h
 ./utf8.o: config.h $(top_srcdir)/./lib.h $(top_srcdir)/./signal.h $(top_srcdir)/./unwind.h $(top_srcdir)/./utf8.h
 ./filter.o: config.h $(top_srcdir)/./lib.h $(top_srcdir)/./hash.h $(top_srcdir)/./signal.h $(top_srcdir)/./unwind.h $(top_srcdir)/./match.h $(top_srcdir)/./filter.h $(top_srcdir)/./gc.h $(top_srcdir)/./stream.h
-./eval.o: config.h $(top_srcdir)/./lib.h $(top_srcdir)/./gc.h $(top_srcdir)/./arith.h $(top_srcdir)/./signal.h $(top_srcdir)/./unwind.h $(top_srcdir)/./regex.h $(top_srcdir)/./stream.h $(top_srcdir)/./parser.h $(top_srcdir)/./hash.h $(top_srcdir)/./debug.h $(top_srcdir)/./match.h $(top_srcdir)/./rand.h $(top_srcdir)/./filter.h $(top_srcdir)/./txr.h $(top_srcdir)/./syslog.h $(top_srcdir)/./eval.h
+./eval.o: config.h $(top_srcdir)/./lib.h $(top_srcdir)/./gc.h $(top_srcdir)/./arith.h $(top_srcdir)/./signal.h $(top_srcdir)/./unwind.h $(top_srcdir)/./regex.h $(top_srcdir)/./stream.h $(top_srcdir)/./parser.h $(top_srcdir)/./hash.h $(top_srcdir)/./debug.h $(top_srcdir)/./match.h $(top_srcdir)/./rand.h $(top_srcdir)/./filter.h $(top_srcdir)/./txr.h $(top_srcdir)/./syslog.h $(top_srcdir)/./combi.h $(top_srcdir)/./eval.h
 ./rand.o: config.h $(top_srcdir)/./lib.h $(top_srcdir)/./signal.h $(top_srcdir)/./unwind.h $(top_srcdir)/./gc.h $(top_srcdir)/./arith.h $(top_srcdir)/./rand.h
+./combi.o: config.h $(top_srcdir)/./lib.h $(top_srcdir)/./signal.h $(top_srcdir)/./unwind.h $(top_srcdir)/./eval.h $(top_srcdir)/./combi.h
 mpi-1.8.6/mpi.o: config.h $(top_srcdir)/mpi-1.8.6/mpi.h $(top_srcdir)/mpi-1.8.6/logtab.h
 mpi-1.8.6/mplogic.o: config.h $(top_srcdir)/mpi-1.8.6/mplogic.h
 ./debug.o: config.h $(top_srcdir)/./lib.h $(top_srcdir)/./debug.h $(top_srcdir)/./gc.h $(top_srcdir)/./signal.h $(top_srcdir)/./unwind.h $(top_srcdir)/./stream.h $(top_srcdir)/./parser.h $(top_srcdir)/./txr.h
diff --git a/eval.c b/eval.c
index 6d1d425f..13ec8e0c 100644
--- a/eval.c
+++ b/eval.c
@@ -61,6 +61,7 @@
 #ifdef HAVE_SYSLOG
 #include "syslog.h"
 #endif
+#include "combi.h"
 #include "eval.h"
 
 typedef val (*opfun_t)(val, val);
@@ -2060,7 +2061,7 @@ static val generate_func(val env, val lcons)
   return nil;
 }
 
-static val generate(val while_pred, val gen_fun)
+val generate(val while_pred, val gen_fun)
 {
   if (!funcall(while_pred)) {
     return nil;
@@ -2125,550 +2126,6 @@ static val force(val promise)
   return rplacd(promise, funcall(cdr(promise)));
 }
 
-static val rperm_while_fun(val env)
-{
-  val vec = cdr(env);
-  return consp(vecref(vec, zero));
-}
-
-static val rperm_gen_fun(val env)
-{
-  cons_bind (list, vec, env);
-  list_collect_decl(out, ptail);
-  cnum i;
-  cnum len = c_num(length_vec(vec));
-
-  for (i = 0; i < len; i++)
-    list_collect(ptail, car(vec->v.vec[i]));
-
-  for (i = len-1; i >= 0; i--) {
-    pop(&vec->v.vec[i]);
-    if (atom(vec->v.vec[i]) && i > 0)
-      vec->v.vec[i] = list;
-    else
-      break;
-  }
-
-  return out;
-}
-
-static val rperm_list(val list, val k)
-{
-  val vec = vector(k, list);
-  val env = cons(list, vec);
-  return generate(func_f0(env, rperm_while_fun),
-                  func_f0(env, rperm_gen_fun));
-}
-
-static val rperm_vec_gen_fun(val env)
-{
-  val list = rperm_gen_fun(env);
-  return vector_list(list);
-}
-
-static val rperm_vec(val ve, val k)
-{
-  val list = list_vector(ve);
-  val vec = vector(k, list);
-  val env = cons(list, vec);
-  return generate(func_f0(env, rperm_while_fun),
-                  func_f0(env, rperm_vec_gen_fun));
-}
-
-static val rperm_str_gen_fun(val env)
-{
-  val list = rperm_gen_fun(env);
-  return cat_str(list, nil);
-}
-
-static val rperm_str(val str, val k)
-{
-  val list = list_str(str);
-  val vec = vector(k, list);
-  val env = cons(list, vec);
-  return generate(func_f0(env, rperm_while_fun),
-                  func_f0(env, rperm_str_gen_fun));
-}
-
-static val rperm(val seq, val k)
-{
-  if (!integerp(k))
-    type_mismatch(lit("rperm: ~s is not an integer"), k, nao);
-
-  if (lt(k, zero))
-    uw_throwf(numeric_error_s, lit("rperm: ~s is not a positive integer"),
-              k, nao);
-
-  switch (type(seq)) {
-  case NIL:
-    if (zerop(k))
-      return cons(nil, nil);
-    return nil;
-  case CONS:
-  case LCONS:
-    if (zerop(k))
-      return cons(nil, nil);
-    return rperm_list(seq, k);
-  case VEC:
-    if (zerop(k))
-      return cons(vector(zero, nil), nil);
-    return rperm_vec(seq, k);
-  case STR:
-  case LSTR:
-  case LIT:
-    if (zerop(k))
-      return cons(string(L""), nil);
-    return rperm_str(seq, k);
-  default:
-    type_mismatch(lit("rperm: ~s is not a sequence"), seq, nao);
-  }
-}
-
-static val perm_while_fun(val state)
-{
-  val p = vecref(state, zero);
-  cnum k = c_num(vecref(state, one));
-  val c = vecref(state, two);
-  cnum n = c_num(length(p));
-  cnum i, j; 
-
-  for (i = k - 1, j = n - k + 1; i >= 0; i--, j++) {
-    cnum ci = c_num(c->v.vec[i]) + 1;
-
-    if (ci >= j) {
-      if (i == 0)
-        return nil;
-      c->v.vec[i] = zero;
-    } else {
-      c->v.vec[i] = num_fast(ci);
-      break;
-    }
-  }
-
-  return t;
-}
-
-static cnum perm_index(cnum n, val b)
-{
-  cnum i, j;
-
-  for (i = 0, j = 0; i < n; i++, j++) {
-    while (b->v.vec[j])
-      j++;
-  }
-
-  while (b->v.vec[j])
-    j++;
-
-  return j;
-}
-
-static void perm_gen_fun_common(val state, val out,
-                                void (*fill)(val out, cnum i, val v))
-{
-  val p = vecref(state, zero);
-  val kk = vecref(state, one);
-  val c = vecref(state, two);
-  val nn = length(p);
-  val b = vector(nn, nil);
-  cnum k = c_num(kk);
-  cnum i; 
-
-  for (i = 0; i < k; i++) {
-    cnum ci = c_num(c->v.vec[i]);
-    cnum j = perm_index(ci, b);
-    fill(out, i, p->v.vec[j]);
-    b->v.vec[j] = t;
-  }
-}
-
-static val perm_init_common(val p, val k_null)
-{
-  uses_or2;
-  val n = length(p);
-  val k = or2(k_null, n);
-
-  if (gt(k, n)) {
-    return nil;
-  } else {
-    val state = vector(three, nil);
-    val c = vector(k, zero);
-    *vecref_l(state, zero) = p;
-    *vecref_l(state, one) = k;
-    *vecref_l(state, two) = c;
-    *vecref_l(c, negone) = negone;
-    return state;
-  }
-}
-
-static void perm_vec_gen_fill(val out, cnum i, val v)
-{
-  out->v.vec[i] = v;
-}
-
-static val perm_vec_gen_fun(val state)
-{
-  val kk = vecref(state, one);
-  val out = vector(kk, nil);
-  perm_gen_fun_common(state, out, perm_vec_gen_fill);
-  return out;
-}
-
-static val perm_vec(val p, val k)
-{
-  k = default_arg(k, length_vec(p));
-
-  if (k == zero) {
-    return cons(vector(zero, nil), nil);
-  } else {
-    val state = perm_init_common(p, k);
-    if (!state)
-      return nil;
-    return generate(func_f0(state, perm_while_fun),
-                    func_f0(state, perm_vec_gen_fun));
-  }
-}
-
-static void perm_list_gen_fill(val out, cnum i, val v)
-{
-  val tail = cdr(out);
-  val nc = cons(v, nil);
-  if (tail)
-    rplacd(tail, nc);
-  else
-    rplaca(out, nc);
-  rplacd(out, nc);
-}
-
-static val perm_list_gen_fun(val state)
-{
-  val out = cons(nil, nil);
-  perm_gen_fun_common(state, out, perm_list_gen_fill);
-  return car(out);
-}
-
-static val perm_list(val p, val k)
-{
-  if (k == zero || (!k && !p)) {
-    return cons(nil, nil);
-  } else {
-    val state = perm_init_common(vector_list(p), k);
-    if (!state)
-      return nil;
-    return generate(func_f0(state, perm_while_fun),
-                    func_f0(state, perm_list_gen_fun));
-  }
-}
-
-static void perm_str_gen_fill(val out, cnum i, val v)
-{
-  out->st.str[i] = c_chr(v);
-}
-
-static val perm_str_gen_fun(val state)
-{
-  val kk = vecref(state, one);
-  val out = mkustring(kk);
-  perm_gen_fun_common(state, out, perm_str_gen_fill);
-  out->st.str[c_num(kk)] = 0;
-  return out;
-}
-
-static val perm_str(val p, val k)
-{
-  k = default_arg(k, length_str(p));
-
-  if (k == zero) {
-    return cons(string(L""), nil);
-  } else {
-    val state = perm_init_common(vector_list(list_str(p)), k);
-    if (!state)
-      return nil;
-    return generate(func_f0(state, perm_while_fun),
-                    func_f0(state, perm_str_gen_fun));
-  }
-}
-
-static val perm(val seq, val k)
-{
-  if (null_or_missing_p(k)) {
-    k = nil;
-  } else {
-    if (!integerp(k))
-      type_mismatch(lit("perm: ~s is not an integer"), k, nao);
-
-    if (lt(k, zero))
-      uw_throwf(numeric_error_s, lit("perm: ~s is not a positive integer"),
-                k, nao);
-  }
-
-  switch (type(seq)) {
-  case CONS:
-  case LCONS:
-  case NIL:
-    return perm_list(seq, k);
-  case VEC:
-    return perm_vec(seq, k);
-  case STR:
-  case LSTR:
-  case LIT:
-    return perm_str(seq, k);
-  default:
-    type_mismatch(lit("perm: ~s is not a sequence"), seq, nao);
-  }
-}
-
-static val k_conses(val list, val k)
-{
-  val iter = list, i = k;
-  list_collect_decl (out, ptail);
-
-  for (; consp(iter) && gt(i, zero); iter = cdr(iter), i = minus(i, one))
-    ptail = list_collect(ptail, iter);
-
-  return (i != zero) ? nil : out;
-}
-
-static val comb_while_fun(val state)
-{
-  return car(state);
-}
-
-static void comb_gen_fun_common(val state)
-{
-  val iter;
-  val prev = nil;
-
-  for (iter = state; consp(iter); iter = cdr(iter)) {
-    val curr = first(iter);
-    val curr_rest = rest(curr);
-    if (curr_rest != prev && consp(curr_rest)) {
-      *car_l(iter) = curr_rest;
-      return;
-    } else if (rest(iter)) {
-      val next = second(iter);
-      val next_rest = rest(next);
-      val next_rest_rest = rest(next_rest);
-      prev = curr;
-      if (next_rest != curr && consp(next_rest_rest))
-        prev = *car_l(iter) = next_rest_rest;
-    } 
-  }
-
-  *car_l(state) = nil;
-}
-
-static val comb_list_gen_fun(val state)
-{
-  val out = nreverse(mapcar(car_f, state));
-  comb_gen_fun_common(state);
-  return out;
-}
-
-static val comb_list(val list, val k)
-{
-  val state = nreverse(k_conses(list, k));
-  return state ? generate(func_f0(state, comb_while_fun),
-                          func_f0(state, comb_list_gen_fun))
-               : nil;
-}
-
-static val comb_vec_gen_fun(val state)
-{
-  val nn = length_list(state);
-  cnum i, n = c_num(nn);
-  val iter, out = vector(nn, nil);
-
-  for (iter = state, i = n - 1; i >= 0; iter = cdr(iter), i--)
-    out->v.vec[i] = car(car(iter));
-
-  comb_gen_fun_common(state);
-  return out;
-}
-
-static val comb_vec(val vec, val k)
-{
-  val state = nreverse(k_conses(list_vector(vec), k));
-  return generate(func_f0(state, comb_while_fun),
-                  func_f0(state, comb_vec_gen_fun));
-}
-
-static val comb_str_gen_fun(val state)
-{
-  val nn = length_list(state);
-  cnum i, n = c_num(nn);
-  val iter, out = mkustring(nn);
-
-  out->st.str[n] = 0;
-
-  for (iter = state, i = n - 1; i >= 0; iter = cdr(iter), i--)
-    out->st.str[i] = c_chr(car(car(iter)));
-
-  comb_gen_fun_common(state);
-  return out;
-}
-
-static val comb_str(val str, val k)
-{
-  val state = nreverse(k_conses(list_str(str), k));
-  return generate(func_f0(state, comb_while_fun),
-                  func_f0(state, comb_str_gen_fun));
-}
-
-static val comb(val seq, val k)
-{
-  if (!integerp(k))
-    type_mismatch(lit("comb: ~s is not an integer"), k, nao);
-
-  if (lt(k, zero))
-    uw_throwf(numeric_error_s, lit("comb: ~s is not a positive integer"),
-              k, nao);
-
-  switch (type(seq)) {
-  case CONS:
-  case LCONS:
-  case NIL:
-    if (k == zero)
-      return cons(nil, nil);
-    return comb_list(seq, k);
-  case VEC:
-    if (k == zero)
-      return cons(vector(zero, nil), nil);
-    if (gt(k, length(seq)))
-      return nil;
-    return comb_vec(seq, k);
-  case STR:
-  case LSTR:
-  case LIT:
-    if (k == zero)
-      return cons(string(L""), nil);
-    if (gt(k, length(seq)))
-      return nil;
-    return comb_str(seq, k);
-  default:
-    type_mismatch(lit("comb: ~s is not a sequence"), seq, nao);
-  }
-}
-
-static val rcomb_while_fun(val state)
-{
-  return car(state);
-}
-
-static void rcomb_gen_fun_common(val state)
-{
-  val iter;
-  val next;
-
-  for (iter = state, next = cdr(state);
-       consp(iter);
-       iter = next, next = cdr(iter))
-  {
-    val curr = first(iter);
-    val curr_rest = rest(curr);
-
-    if (consp(curr_rest)) {
-      val jter;
-      for (jter = state; jter != next; jter = cdr(jter))
-        *car_l(jter) = curr_rest;
-      return;
-    } else if (next) {
-      val next = second(iter);
-      if (curr != next)
-        *car_l(iter) = rest(next);
-    } 
-  }
-
-  *car_l(state) = nil;
-}
-
-static val rcomb_list_gen_fun(val state)
-{
-  val out = nreverse(mapcar(car_f, state));
-  rcomb_gen_fun_common(state);
-  return out;
-}
-
-static val rcomb_list(val list, val k)
-{
-  val state = nreverse(list_vector(vector(k, list)));
-  return generate(func_f0(state, rcomb_while_fun),
-                  func_f0(state, rcomb_list_gen_fun));
-}
-
-static val rcomb_vec_gen_fun(val state)
-{
-  val nn = length_list(state);
-  cnum i, n = c_num(nn);
-  val iter, out = vector(nn, nil);
-
-  for (iter = state, i = n - 1; i >= 0; iter = cdr(iter), i--)
-    out->v.vec[i] = car(car(iter));
-
-  rcomb_gen_fun_common(state);
-  return out;
-}
-
-static val rcomb_vec(val vec, val k)
-{
-  val state = nreverse(list_vector(vector(k, list_vector(vec))));
-  return generate(func_f0(state, rcomb_while_fun),
-                  func_f0(state, rcomb_vec_gen_fun));
-}
-
-static val rcomb_str_gen_fun(val state)
-{
-  val nn = length_list(state);
-  cnum i, n = c_num(nn);
-  val iter, out = mkustring(nn);
-
-  out->st.str[n] = 0;
-
-  for (iter = state, i = n - 1; i >= 0; iter = cdr(iter), i--)
-    out->st.str[i] = c_chr(car(car(iter)));
-
-  rcomb_gen_fun_common(state);
-  return out;
-}
-
-static val rcomb_str(val str, val k)
-{
-  val state = nreverse(list_vector(vector(k, list_str(str))));
-  return generate(func_f0(state, rcomb_while_fun),
-                  func_f0(state, rcomb_str_gen_fun));
-}
-
-static val rcomb(val seq, val k)
-{
-  if (!integerp(k))
-    type_mismatch(lit("rcomb: ~s is not an integer"), k, nao);
-
-  if (lt(k, zero))
-    uw_throwf(numeric_error_s, lit("rcomb: ~s is not a positive integer"),
-              k, nao);
-
-  switch (type(seq)) {
-  case CONS:
-  case LCONS:
-  case NIL:
-    if (k == zero)
-      return cons(nil, nil);
-    return rcomb_list(seq, k);
-  case VEC:
-    if (k == zero)
-      return cons(vector(zero, nil), nil);
-    return rcomb_vec(seq, k);
-  case STR:
-  case LSTR:
-  case LIT:
-    if (k == zero)
-      return cons(string(L""), nil);
-    return rcomb_str(seq, k);
-  default:
-    type_mismatch(lit("rcomb: ~s is not a sequence"), seq, nao);
-  }
-}
-
 static val errno_wrap(val newval)
 {
   val oldval = num(errno);
diff --git a/eval.h b/eval.h
index 5389320d..03bfea23 100644
--- a/eval.h
+++ b/eval.h
@@ -42,5 +42,6 @@ val expand(val form);
 val expand_forms(val forms);
 val bindable(val obj);
 val mapcarv(val fun, val list_of_lists);
+val generate(val while_pred, val gen_fun);
 
 void eval_init(void);
diff --git a/txr.vim b/txr.vim
index 37eedda5..cd49e35d 100644
--- a/txr.vim
+++ b/txr.vim
@@ -52,73 +52,74 @@ syn keyword txl_keyword contained chr-isgraph chr-islower chr-isprint chr-ispunc
 syn keyword txl_keyword contained chr-isspace chr-isupper chr-isxdigit chr-num
 syn keyword txl_keyword contained chr-str chr-str-set chr-tolower chr-toupper
 syn keyword txl_keyword contained chrp close-stream closelog collect-each
-syn keyword txl_keyword contained collect-each* compl-span-str cond cons
-syn keyword txl_keyword contained conses conses* consp copy-alist
-syn keyword txl_keyword contained copy-cons copy-hash copy-list copy-str
-syn keyword txl_keyword contained copy-vec cos count-if countq
-syn keyword txl_keyword contained countql countqual cum-norm-dist daemon
-syn keyword txl_keyword contained dec defun defvar del
-syn keyword txl_keyword contained delete-package do dohash downcase-str
-syn keyword txl_keyword contained dwim each each* eq
-syn keyword txl_keyword contained eql equal errno error
-syn keyword txl_keyword contained eval evenp exit exp
-syn keyword txl_keyword contained expand expt exptmod fboundp
-syn keyword txl_keyword contained fifth find find-if find-package
-syn keyword txl_keyword contained first fixnump flatten flatten*
-syn keyword txl_keyword contained flip flo-int flo-str floatp
-syn keyword txl_keyword contained floor flush-stream for for*
-syn keyword txl_keyword contained force format fourth fun
-syn keyword txl_keyword contained func-get-env func-get-form func-set-env functionp
-syn keyword txl_keyword contained gcd generate gensym get-byte
-syn keyword txl_keyword contained get-char get-hash-userdata get-line get-list-from-stream
-syn keyword txl_keyword contained get-sig-handler get-string-from-stream gethash group-by
-syn keyword txl_keyword contained hash hash-alist hash-construct hash-count
-syn keyword txl_keyword contained hash-diff hash-eql hash-equal hash-isec
-syn keyword txl_keyword contained hash-keys hash-pairs hash-uni hash-update
-syn keyword txl_keyword contained hash-values hashp identity if
-syn keyword txl_keyword contained iff iffi inc int-flo
-syn keyword txl_keyword contained int-str integerp intern interp-fun-p
-syn keyword txl_keyword contained isqrt keep-if keep-if* keywordp
-syn keyword txl_keyword contained lambda lazy-str lazy-str-force lazy-str-force-upto
-syn keyword txl_keyword contained lazy-str-get-trailing-list lazy-stream-cons lazy-stringp lcons-fun
-syn keyword txl_keyword contained ldiff length length-list length-str
-syn keyword txl_keyword contained length-str-< length-str-<= length-str-> length-str->=
-syn keyword txl_keyword contained length-vec let let* lisp-parse
-syn keyword txl_keyword contained list list* list-str list-vector
-syn keyword txl_keyword contained listp log log-alert log-auth
-syn keyword txl_keyword contained log-authpriv log-cons log-crit log-daemon
-syn keyword txl_keyword contained log-debug log-emerg log-err log-info
-syn keyword txl_keyword contained log-ndelay log-notice log-nowait log-odelay
-syn keyword txl_keyword contained log-perror log-pid log-user log-warning
-syn keyword txl_keyword contained logand logior lognot logtest
-syn keyword txl_keyword contained logtrunc logxor make-catenated-stream make-hash
-syn keyword txl_keyword contained make-lazy-cons make-package make-random-state make-similar-hash
-syn keyword txl_keyword contained make-string-byte-input-stream make-string-input-stream make-string-output-stream make-strlist-output-stream
-syn keyword txl_keyword contained make-sym make-time make-time-utc mapcar
-syn keyword txl_keyword contained mapcar* maphash mappend mappend*
-syn keyword txl_keyword contained mask match-fun match-regex match-regex-right
-syn keyword txl_keyword contained match-str match-str-tree max memq
-syn keyword txl_keyword contained memql memqual merge min
-syn keyword txl_keyword contained mkstring mod multi-sort n-choose-k
-syn keyword txl_keyword contained n-perm-k none not nreverse
-syn keyword txl_keyword contained null num-chr num-str numberp
-syn keyword txl_keyword contained oddp op open-command open-directory
-syn keyword txl_keyword contained open-file open-pipe open-process open-tail
-syn keyword txl_keyword contained openlog or orf packagep
-syn keyword txl_keyword contained pop pprint print prog1
-syn keyword txl_keyword contained progn prop proper-listp push
-syn keyword txl_keyword contained pushhash put-byte put-char put-line
-syn keyword txl_keyword contained put-string qquote quasi quote
-syn keyword txl_keyword contained rand random random-fixnum random-state-p
-syn keyword txl_keyword contained range range* read real-time-stream-p
-syn keyword txl_keyword contained reduce-left reduce-right ref refset
-syn keyword txl_keyword contained regex-compile regex-parse regexp regsub
-syn keyword txl_keyword contained rehome-sym remhash remove-if remove-if*
-syn keyword txl_keyword contained remove-path remq remq* remql
-syn keyword txl_keyword contained remql* remqual remqual* rename-path
-syn keyword txl_keyword contained repeat replace replace-list replace-str
-syn keyword txl_keyword contained replace-vec rest return return-from
-syn keyword txl_keyword contained reverse rplaca rplacd s-ifblk
+syn keyword txl_keyword contained collect-each* comb compl-span-str cond
+syn keyword txl_keyword contained cons conses conses* consp
+syn keyword txl_keyword contained copy-alist copy-cons copy-hash copy-list
+syn keyword txl_keyword contained copy-str copy-vec cos count-if
+syn keyword txl_keyword contained countq countql countqual cum-norm-dist
+syn keyword txl_keyword contained daemon dec defun defvar
+syn keyword txl_keyword contained del delete-package do dohash
+syn keyword txl_keyword contained downcase-str dwim each each*
+syn keyword txl_keyword contained eq eql equal errno
+syn keyword txl_keyword contained error eval evenp exit
+syn keyword txl_keyword contained exp expand expt exptmod
+syn keyword txl_keyword contained fboundp fifth find find-if
+syn keyword txl_keyword contained find-package first fixnump flatten
+syn keyword txl_keyword contained flatten* flip flo-int flo-str
+syn keyword txl_keyword contained floatp floor flush-stream for
+syn keyword txl_keyword contained for* force format fourth
+syn keyword txl_keyword contained fun func-get-env func-get-form func-set-env
+syn keyword txl_keyword contained functionp gcd generate gensym
+syn keyword txl_keyword contained get-byte get-char get-hash-userdata get-line
+syn keyword txl_keyword contained get-list-from-stream get-sig-handler get-string-from-stream gethash
+syn keyword txl_keyword contained group-by hash hash-alist hash-construct
+syn keyword txl_keyword contained hash-count hash-diff hash-eql hash-equal
+syn keyword txl_keyword contained hash-isec hash-keys hash-pairs hash-uni
+syn keyword txl_keyword contained hash-update hash-values hashp identity
+syn keyword txl_keyword contained if iff iffi inc
+syn keyword txl_keyword contained int-flo int-str integerp intern
+syn keyword txl_keyword contained interp-fun-p isqrt keep-if keep-if*
+syn keyword txl_keyword contained keywordp lambda lazy-str lazy-str-force
+syn keyword txl_keyword contained lazy-str-force-upto lazy-str-get-trailing-list lazy-stream-cons lazy-stringp
+syn keyword txl_keyword contained lcons-fun ldiff length length-list
+syn keyword txl_keyword contained length-str length-str-< length-str-<= length-str->
+syn keyword txl_keyword contained length-str->= length-vec let let*
+syn keyword txl_keyword contained lisp-parse list list* list-str
+syn keyword txl_keyword contained list-vector listp log log-alert
+syn keyword txl_keyword contained log-auth log-authpriv log-cons log-crit
+syn keyword txl_keyword contained log-daemon log-debug log-emerg log-err
+syn keyword txl_keyword contained log-info log-ndelay log-notice log-nowait
+syn keyword txl_keyword contained log-odelay log-perror log-pid log-user
+syn keyword txl_keyword contained log-warning logand logior lognot
+syn keyword txl_keyword contained logtest logtrunc logxor make-catenated-stream
+syn keyword txl_keyword contained make-hash make-lazy-cons make-package make-random-state
+syn keyword txl_keyword contained make-similar-hash make-string-byte-input-stream make-string-input-stream make-string-output-stream
+syn keyword txl_keyword contained make-strlist-output-stream make-sym make-time make-time-utc
+syn keyword txl_keyword contained mapcar mapcar* maphash mappend
+syn keyword txl_keyword contained mappend* mask match-fun match-regex
+syn keyword txl_keyword contained match-regex-right match-str match-str-tree max
+syn keyword txl_keyword contained memq memql memqual merge
+syn keyword txl_keyword contained min mkstring mod multi-sort
+syn keyword txl_keyword contained n-choose-k n-perm-k none not
+syn keyword txl_keyword contained nreverse null num-chr num-str
+syn keyword txl_keyword contained numberp oddp op open-command
+syn keyword txl_keyword contained open-directory open-file open-pipe open-process
+syn keyword txl_keyword contained open-tail openlog or orf
+syn keyword txl_keyword contained packagep perm pop pprint
+syn keyword txl_keyword contained print prog1 progn prop
+syn keyword txl_keyword contained proper-listp push pushhash put-byte
+syn keyword txl_keyword contained put-char put-line put-string qquote
+syn keyword txl_keyword contained quasi quote rand random
+syn keyword txl_keyword contained random-fixnum random-state-p range range*
+syn keyword txl_keyword contained rcomb read real-time-stream-p reduce-left
+syn keyword txl_keyword contained reduce-right ref refset regex-compile
+syn keyword txl_keyword contained regex-parse regexp regsub rehome-sym
+syn keyword txl_keyword contained remhash remove-if remove-if* remove-path
+syn keyword txl_keyword contained remq remq* remql remql*
+syn keyword txl_keyword contained remqual remqual* rename-path repeat
+syn keyword txl_keyword contained replace replace-list replace-str replace-vec
+syn keyword txl_keyword contained rest return return-from reverse
+syn keyword txl_keyword contained rperm rplaca rplacd s-ifblk
 syn keyword txl_keyword contained s-ifchr s-ifdir s-ififo s-iflnk
 syn keyword txl_keyword contained s-ifmt s-ifreg s-irgrp s-iroth
 syn keyword txl_keyword contained s-irusr s-irwxg s-irwxo s-irwxu