diff --git a/critbit.c b/critbit.c
index c0606f9..1815449 100644
--- a/critbit.c
+++ b/critbit.c
@@ -258,14 +258,23 @@ int tt_dict_foreach(tt_arena_t *a,
   }
 }
 
+struct tt_dictset_union_context {
+  tt_arena_t *a;
+  tt_node_ptr_t result;
+};
+
+static int tt_dictset_union_f(void *context, tt_atom_t key, tt_node_ptr_t ignored_trie) {
+  struct tt_dictset_union_context *c = (struct tt_dictset_union_context *) context;
+  tt_node_ptr_t new_result = tt_grab(c->a, tt_dict_set(c->a, c->result, key, TT_EMPTY));
+  tt_drop(c->a, c->result);
+  c->result = new_result;
+  return !TT_NO_PTR_P(c->result);
+}
+
 tt_node_ptr_t tt_dictset_union(tt_arena_t *a, tt_node_ptr_t s1, tt_node_ptr_t s2) {
-  tt_node_ptr_t result = TT_NO_PTR; /* grab'd */
-  int f(void *context, tt_atom_t key, tt_node_ptr_t ignored_trie) {
-    tt_node_ptr_t new_result = tt_grab(a, tt_dict_set(a, result, key, TT_EMPTY));
-    tt_drop(a, result);
-    result = new_result;
-    return !TT_NO_PTR_P(result);
-  }
+  struct tt_dictset_union_context context;
+  context.a = a;
+  context.result = TT_NO_PTR; /* grab'd */
 
   if (tt_dict_size(a, s1) < tt_dict_size(a, s2)) {
     tt_node_ptr_t tmp = s2;
@@ -273,55 +282,76 @@ tt_node_ptr_t tt_dictset_union(tt_arena_t *a, tt_node_ptr_t s1, tt_node_ptr_t s2
     s1 = tmp;
   }
   /* Now s1 is larger, s2 is smaller. */
-  result = tt_grab(a, s1);
-  tt_dict_foreach(a, s2, NULL, f);
-  return result;
+  context.result = tt_grab(a, s1);
+  tt_dict_foreach(a, s2, &context, tt_dictset_union_f);
+  return context.result;
+}
+
+struct tt_dictset_intersection_context {
+  tt_arena_t *a;
+  tt_node_ptr_t s1;
+  tt_node_ptr_t result;
+};
+
+static int tt_dictset_intersection_f(void *context, tt_atom_t key, tt_node_ptr_t ignored_trie) {
+  struct tt_dictset_intersection_context *c = (struct tt_dictset_intersection_context *) context;
+  if (!TT_NO_PTR_P(tt_dict_get(c->a, c->s1, key))) {
+    tt_node_ptr_t new_result = tt_grab(c->a, tt_dict_set(c->a, c->result, key, TT_EMPTY));
+    tt_drop(c->a, c->result);
+    c->result = new_result;
+  }
+  return !TT_NO_PTR_P(c->result);
 }
 
 tt_node_ptr_t tt_dictset_intersection(tt_arena_t *a, tt_node_ptr_t s1, tt_node_ptr_t s2) {
-  tt_node_ptr_t result = TT_NO_PTR; /* grab'd */
-  int f(void *context, tt_atom_t key, tt_node_ptr_t ignored_trie) {
-    if (!TT_NO_PTR_P(tt_dict_get(a, s1, key))) {
-      tt_node_ptr_t new_result = tt_grab(a, tt_dict_set(a, result, key, TT_EMPTY));
-      tt_drop(a, result);
-      result = new_result;
-    }
-    return !TT_NO_PTR_P(result);
-  }
-
+  struct tt_dictset_intersection_context context;
   if (tt_dict_size(a, s1) < tt_dict_size(a, s2)) {
     tt_node_ptr_t tmp = s2;
     s2 = s1;
     s1 = tmp;
   }
   /* Now s1 is larger, s2 is smaller. */
-  result = TT_EMPTY_DICT;
-  tt_dict_foreach(a, s2, NULL, f);
-  return result;
+  context.a = a;
+  context.s1 = s1;
+  context.result = TT_EMPTY_DICT; /* grab'd */
+  tt_dict_foreach(a, s2, &context, tt_dictset_intersection_f);
+  return context.result;
+}
+
+struct tt_dictset_difference_context {
+  tt_arena_t *a;
+  tt_node_ptr_t s2;
+  tt_node_ptr_t result;
+};
+
+static int tt_dictset_difference_f1(void *context, tt_atom_t key, tt_node_ptr_t ignored_trie) {
+  struct tt_dictset_difference_context *c = (struct tt_dictset_difference_context *) context;
+  if (!TT_NO_PTR_P(tt_dict_get(c->a, c->s2, key))) {
+    tt_node_ptr_t new_result = tt_grab(c->a, tt_dict_set(c->a, c->result, key, TT_EMPTY));
+    tt_drop(c->a, c->result);
+    c->result = new_result;
+  }
+  return !TT_NO_PTR_P(c->result);
+}
+
+static int tt_dictset_difference_f2(void *context, tt_atom_t key, tt_node_ptr_t ignored_trie) {
+  struct tt_dictset_difference_context *c = (struct tt_dictset_difference_context *) context;
+  tt_node_ptr_t new_result = tt_grab(c->a, tt_dict_remove(c->a, c->result, key));
+  tt_drop(c->a, c->result);
+  c->result = new_result;
+  return !TT_NO_PTR_P(c->result);
 }
 
 tt_node_ptr_t tt_dictset_difference(tt_arena_t *a, tt_node_ptr_t s1, tt_node_ptr_t s2) {
-  tt_node_ptr_t result = TT_NO_PTR;
+  struct tt_dictset_difference_context context;
+  context.a = a;
+  context.s2 = s2;
   if (tt_dict_size(a, s1) < tt_dict_size(a, s2)) {
-    int f(void *context, tt_atom_t key, tt_node_ptr_t ignored_trie) {
-      if (!TT_NO_PTR_P(tt_dict_get(a, s2, key))) {
-	tt_node_ptr_t new_result = tt_grab(a, tt_dict_set(a, result, key, TT_EMPTY));
-	tt_drop(a, result);
-	result = new_result;
-      }
-      return !TT_NO_PTR_P(result);
-    }
-    result = TT_EMPTY_DICT;
-    tt_dict_foreach(a, s1, NULL, f);
+    context.result = TT_EMPTY_DICT;
+    tt_dict_foreach(a, s1, &context, tt_dictset_difference_f1);
   } else {
-    int f(void *context, tt_atom_t key, tt_node_ptr_t ignored_trie) {
-      tt_node_ptr_t new_result = tt_grab(a, tt_dict_remove(a, result, key));
-      tt_drop(a, result);
-      result = new_result;
-      return !TT_NO_PTR_P(result);
-    }
-    result = tt_grab(a, s1);
-    tt_dict_foreach(a, s2, NULL, f);
+    context.result = tt_grab(a, s1);
+    tt_dict_foreach(a, s2, &context, tt_dictset_difference_f2);
   }
-  return result;
+  return context.result;
 }
diff --git a/route.c b/route.c
index 1018c54..c58292b 100644
--- a/route.c
+++ b/route.c
@@ -160,6 +160,179 @@ static inline tt_node_ptr_t collapse(tt_arena_t *a, tt_node_ptr_t n) {
   return n;
 }
 
+struct tt_trie_combine_context {
+  tt_arena_t *a;
+  int left_empty_keep;
+  int right_empty_keep;
+  int left_base_keep;
+  int right_base_keep;
+  void *f_context;
+  /* Should return a tt_grab'd result. */
+  tt_node_ptr_t (*f)(void *f_context, tt_node_ptr_t r1, tt_node_ptr_t r2);
+};
+
+struct tt_trie_combine_examine_key_context {
+  struct tt_trie_combine_context *c;
+  tt_arena_t *a; /* the same as from tt_trie_combine_context */
+  tt_node_ptr_t w1;
+  tt_node_ptr_t w2;
+  tt_node_ptr_t dict1;
+  tt_node_ptr_t dict2;
+  tt_node_ptr_t result_wild; /* grab'd */
+  tt_node_ptr_t result_others; /* grab'd */
+};
+
+/* Forward declaration (mutual recursion) */
+static tt_node_ptr_t tt_trie_combine_g(struct tt_trie_combine_context *c,
+				       tt_node_ptr_t r1,
+				       tt_node_ptr_t r2);
+
+static int tt_trie_combine_examine_key(void *examine_key_context,
+				       tt_atom_t key,
+				       tt_node_ptr_t ignored_trie)
+{
+  struct tt_trie_combine_examine_key_context *c =
+    (struct tt_trie_combine_examine_key_context *) examine_key_context;
+  tt_arena_t *a = c->a;
+  tt_node_ptr_t trie1, trie2; /* Looked up in r1 and r2 */
+  tt_node_ptr_t new_trie; /* Combination of trie1 and trie2 */
+  tt_node_ptr_t new_result_others; /* Updated dictionary with key---new_trie association */
+
+  trie1 = tt_grab(a, rlookup_dict(a, c->w1, c->dict1, key));
+  if (TT_NO_PTR_P(trie1)) return 0;
+  trie2 = tt_grab(a, rlookup_dict(a, c->w2, c->dict2, key));
+  if (TT_NO_PTR_P(trie2)) {
+    tt_drop(a, trie1);
+    return 0;
+  }
+  /* printf("descending into key %d, trie1 %u/%u trie2 %u/%u\n", */
+  /*        key, */
+  /*        tt_ptr_idx(trie1), */
+  /*        tt_ptr_tag(trie1), */
+  /*        tt_ptr_idx(trie2), */
+  /*        tt_ptr_tag(trie2)); */
+  new_trie = tt_trie_combine_g(c->c, trie1, trie2); /* already grabbed */
+  tt_drop(a, trie1);
+  tt_drop(a, trie2);
+  if (TT_NO_PTR_P(new_trie)) return 0;
+  new_result_others = tt_grab(a, rupdate_dict(a, c->result_wild, c->result_others, key, new_trie));
+  tt_drop(a, new_trie);
+  if (TT_NO_PTR_P(new_result_others)) return 0;
+  tt_drop(a, c->result_others);
+  c->result_others = new_result_others;
+  /* printf("after update key %d, result_others %u/%u\n", */
+  /*        key, */
+  /*        tt_ptr_idx(c->result_others), */
+  /*        tt_ptr_tag(c->result_others)); */
+  return 1;
+}
+
+/* N.B. Returns a tt_grab'd result. */
+static tt_node_ptr_t tt_trie_combine_g(struct tt_trie_combine_context *c,
+				       tt_node_ptr_t r1,
+				       tt_node_ptr_t r2)
+{
+  tt_arena_t *a = c->a;
+  tt_tag_t t1, t2;
+
+  if (TT_EMPTY_P(r1)) {
+    return c->left_empty_keep ? tt_grab(a, r2) : TT_EMPTY;
+  }
+  if (TT_EMPTY_P(r2)) {
+    return c->right_empty_keep ? tt_grab(a, r1) : TT_EMPTY;
+  }
+
+  t1 = tt_ptr_tag(r1);
+  t2 = tt_ptr_tag(r2);
+
+  if (t1 == TT_TAG_BRANCH && t2 == TT_TAG_BRANCH) {
+    tt_node_ptr_t result = TT_NO_PTR; /* grab'd */
+    struct tt_trie_combine_examine_key_context ekc;
+    int ok = 1;
+
+    ekc.c = c;
+    ekc.a = a;
+    ekc.w1 = TT_BRANCH_WILDCARD(a,r1);
+    ekc.w2 = TT_BRANCH_WILDCARD(a,r2);
+    ekc.dict1 = TT_BRANCH_OTHERS(a,r1);
+    ekc.dict2 = TT_BRANCH_OTHERS(a,r2);
+    ekc.result_wild = TT_EMPTY; /* grab'd */
+    ekc.result_others = TT_EMPTY_DICT; /* grab'd */
+
+    /* printf("{{{ combining %u/%u with %u/%u\n", */
+    /* 	     tt_ptr_idx(r1), */
+    /* 	     tt_ptr_tag(r1), */
+    /* 	     tt_ptr_idx(r2), */
+    /* 	     tt_ptr_tag(r2)); */
+    if (!TT_EMPTY_P(ekc.w1) && !TT_EMPTY_P(ekc.w2)) {
+      /* Two wildcards - worst case. Must loop over both dictionaries. */
+      ekc.result_wild = tt_trie_combine_g(c, ekc.w1, ekc.w2);
+      ok = !TT_NO_PTR_P(ekc.result_wild);
+      ok = ok && tt_dict_foreach(a, ekc.dict1, &ekc, tt_trie_combine_examine_key);
+      ok = ok && tt_dict_foreach(a, ekc.dict2, &ekc, tt_trie_combine_examine_key);
+    } else if ((!TT_EMPTY_P(ekc.w1)) ||
+	       (TT_EMPTY_P(ekc.w2) &&
+		(tt_dict_size(a, ekc.dict1) >= tt_dict_size(a, ekc.dict2)))) {
+      /* Either a wildcard on the left, or no wildcard at all but the left is larger */
+      if (c->left_base_keep) {
+	ekc.result_wild = tt_grab(a, ekc.w1);
+	ekc.result_others = tt_grab(a, ekc.dict1);
+      }
+      ok = ok && tt_dict_foreach(a, ekc.dict2, &ekc, tt_trie_combine_examine_key);
+    } else {
+      /* Either a wildcard on the right, or no wildcard at all but the right is larger */
+      if (c->right_base_keep) {
+	ekc.result_wild = tt_grab(a, ekc.w2);
+	ekc.result_others = tt_grab(a, ekc.dict2);
+      }
+      ok = ok && tt_dict_foreach(a, ekc.dict1, &ekc, tt_trie_combine_examine_key);
+    }
+
+    if (ok) {
+      result = tt_grab(a, rbranch(a, ekc.result_wild, ekc.result_others));
+      if (!TT_NO_PTR_P(result)) {
+	tt_node_ptr_t collapsed = tt_grab(a, collapse(a, result));
+	tt_drop(a, result);
+	result = collapsed;
+      }
+    }
+    /* printf("}}} result %u/%u\n", */
+    /* 	     tt_ptr_idx(result), */
+    /* 	     tt_ptr_tag(result)); */
+
+    tt_drop(a, ekc.result_wild);
+    tt_drop(a, ekc.result_others);
+    return result;
+  }
+
+  if (t1 == TT_TAG_TAIL) {
+    if (t2 == TT_TAG_TAIL) {
+      tt_node_ptr_t combined =
+	RET_IF_NO_PTR(tt_trie_combine_g(c, TT_TAIL_TRIE(a,r1), TT_TAIL_TRIE(a,r2)));
+      tt_node_ptr_t result = tt_grab(a, rwildseq(a, combined));
+      tt_drop(a, combined);
+      return result;
+    } else {
+      tt_node_ptr_t r1_expanded = tt_grab(a, RET_IF_NO_PTR(expand(a, r1)));
+      tt_node_ptr_t result = tt_trie_combine_g(c, r1_expanded, r2);
+      tt_drop(a, r1_expanded);
+      return result;
+    }
+  } else if (t2 == TT_TAG_TAIL) {
+    tt_node_ptr_t r2_expanded = tt_grab(a, RET_IF_NO_PTR(expand(a, r2)));
+    tt_node_ptr_t result = tt_trie_combine_g(c, r1, r2_expanded);
+    tt_drop(a, r2_expanded);
+    return result;
+  }
+
+  if (t1 == TT_TAG_OK || t2 == TT_TAG_OK) {
+    return c->f(c->f_context, r1, r2);
+  }
+
+  /* There is no legitimate combination of tags that should let us get here. */
+  assert(0);
+}
+
 /* N.B. Returns a tt_grab'd result. */
 tt_node_ptr_t tt_trie_combine(tt_arena_t *a,
 			      tt_node_ptr_t r1,
@@ -174,174 +347,64 @@ tt_node_ptr_t tt_trie_combine(tt_arena_t *a,
 						 tt_node_ptr_t r1,
 						 tt_node_ptr_t r2))
 {
-  /* N.B. Returns a tt_grab'd result. */
-  tt_node_ptr_t g(tt_node_ptr_t r1, tt_node_ptr_t r2) {
-    tt_tag_t t1, t2;
+  struct tt_trie_combine_context context;
+  context.a = a;
+  context.left_empty_keep = left_empty_keep;
+  context.right_empty_keep = right_empty_keep;
+  context.left_base_keep = left_base_keep;
+  context.right_base_keep = right_base_keep;
+  context.f_context = f_context;
+  context.f = f;
+  /* No need for tt_grab here - tt_trie_combine_g has already done that for us */
+  return tt_trie_combine_g(&context, r1, r2);
+}
 
-    if (TT_EMPTY_P(r1)) {
-      return left_empty_keep ? tt_grab(a, r2) : TT_EMPTY;
-    }
-    if (TT_EMPTY_P(r2)) {
-      return right_empty_keep ? tt_grab(a, r1) : TT_EMPTY;
-    }
-
-    t1 = tt_ptr_tag(r1);
-    t2 = tt_ptr_tag(r2);
-
-    if (t1 == TT_TAG_BRANCH && t2 == TT_TAG_BRANCH) {
-      tt_node_ptr_t w1 = TT_BRANCH_WILDCARD(a,r1);
-      tt_node_ptr_t w2 = TT_BRANCH_WILDCARD(a,r2);
-      tt_node_ptr_t dict1 = TT_BRANCH_OTHERS(a,r1);
-      tt_node_ptr_t dict2 = TT_BRANCH_OTHERS(a,r2);
-      tt_node_ptr_t result_wild = TT_EMPTY; /* grab'd */
-      tt_node_ptr_t result_others = TT_EMPTY_DICT; /* grab'd */
-      tt_node_ptr_t result = TT_NO_PTR; /* grab'd */
-      int ok = 1;
-
-      int examine_key(void *examine_key_context, tt_atom_t key, tt_node_ptr_t ignored_trie) {
-	tt_node_ptr_t trie1, trie2; /* Looked up in r1 and r2 */
-	tt_node_ptr_t new_trie; /* Combination of trie1 and trie2 */
-	tt_node_ptr_t new_result_others; /* Updated dictionary with key---new_trie association */
-	trie1 = tt_grab(a, rlookup_dict(a, w1, dict1, key));
-	if (TT_NO_PTR_P(trie1)) return 0;
-	trie2 = tt_grab(a, rlookup_dict(a, w2, dict2, key));
-	if (TT_NO_PTR_P(trie2)) {
-	  tt_drop(a, trie1);
-	  return 0;
-	}
-	/* printf("descending into key %d, trie1 %u/%u trie2 %u/%u\n", */
-	/*        key, */
-	/*        tt_ptr_idx(trie1), */
-	/*        tt_ptr_tag(trie1), */
-	/*        tt_ptr_idx(trie2), */
-	/*        tt_ptr_tag(trie2)); */
-	new_trie = g(trie1, trie2); /* already grabbed */
-	tt_drop(a, trie1);
-	tt_drop(a, trie2);
-	if (TT_NO_PTR_P(new_trie)) return 0;
-	new_result_others = tt_grab(a, rupdate_dict(a, result_wild, result_others, key, new_trie));
-	tt_drop(a, new_trie);
-	if (TT_NO_PTR_P(new_result_others)) return 0;
-	tt_drop(a, result_others);
-	result_others = new_result_others;
-	/* printf("after update key %d, result_others %u/%u\n", */
-	/*        key, */
-	/*        tt_ptr_idx(result_others), */
-	/*        tt_ptr_tag(result_others)); */
-	return 1;
-      }
-
-      /* printf("{{{ combining %u/%u with %u/%u\n", */
-      /* 	     tt_ptr_idx(r1), */
-      /* 	     tt_ptr_tag(r1), */
-      /* 	     tt_ptr_idx(r2), */
-      /* 	     tt_ptr_tag(r2)); */
-      if (!TT_EMPTY_P(w1) && !TT_EMPTY_P(w2)) {
-	/* Two wildcards - worst case. Must loop over both dictionaries. */
-	result_wild = g(w1, w2);
-	ok = !TT_NO_PTR_P(result_wild);
-	ok = ok && tt_dict_foreach(a, dict1, NULL, examine_key);
-	ok = ok && tt_dict_foreach(a, dict2, NULL, examine_key);
-      } else if ((!TT_EMPTY_P(w1)) ||
-		 (TT_EMPTY_P(w2) &&
-		  (tt_dict_size(a, dict1) >= tt_dict_size(a, dict2)))) {
-	/* Either a wildcard on the left, or no wildcard at all but the left is larger */
-	if (left_base_keep) {
-	  result_wild = tt_grab(a, w1);
-	  result_others = tt_grab(a, dict1);
-	}
-	ok = ok && tt_dict_foreach(a, dict2, NULL, examine_key);
-      } else {
-	/* Either a wildcard on the right, or no wildcard at all but the right is larger */
-	if (right_base_keep) {
-	  result_wild = tt_grab(a, w2);
-	  result_others = tt_grab(a, dict2);
-	}
-	ok = ok && tt_dict_foreach(a, dict1, NULL, examine_key);
-      }
-
-      if (ok) {
-	result = tt_grab(a, rbranch(a, result_wild, result_others));
-	if (!TT_NO_PTR_P(result)) {
-	  tt_node_ptr_t collapsed = tt_grab(a, collapse(a, result));
-	  tt_drop(a, result);
-	  result = collapsed;
-	}
-      }
-      /* printf("}}} result %u/%u\n", */
-      /* 	     tt_ptr_idx(result), */
-      /* 	     tt_ptr_tag(result)); */
-
-      tt_drop(a, result_wild);
-      tt_drop(a, result_others);
-      return result;
-    }
-
-    if (t1 == TT_TAG_TAIL) {
-      if (t2 == TT_TAG_TAIL) {
-	tt_node_ptr_t combined = RET_IF_NO_PTR(g(TT_TAIL_TRIE(a,r1), TT_TAIL_TRIE(a,r2)));
-	tt_node_ptr_t result = tt_grab(a, rwildseq(a, combined));
-	tt_drop(a, combined);
-	return result;
-      } else {
-	tt_node_ptr_t r1_expanded = tt_grab(a, RET_IF_NO_PTR(expand(a, r1)));
-	tt_node_ptr_t result = g(r1_expanded, r2);
-	tt_drop(a, r1_expanded);
-	return result;
-      }
-    } else if (t2 == TT_TAG_TAIL) {
-      tt_node_ptr_t r2_expanded = tt_grab(a, RET_IF_NO_PTR(expand(a, r2)));
-      tt_node_ptr_t result = g(r1, r2_expanded);
-      tt_drop(a, r2_expanded);
-      return result;
-    }
-
-    if (t1 == TT_TAG_OK || t2 == TT_TAG_OK) {
-      return f(f_context, r1, r2);
-    }
-
-    /* There is no legitimate combination of tags that should let us get here. */
-    assert(0);
+static tt_node_ptr_t f_union_map(void *f_context, tt_node_ptr_t r1, tt_node_ptr_t r2) {
+  tt_arena_t *a = (tt_arena_t *) f_context;
+  tt_tag_t t1 = tt_ptr_tag(r1);
+  tt_tag_t t2 = tt_ptr_tag(r2);
+  if (t1 != TT_TAG_OK) {
+    /* t2 must be ok. */
+    return tt_grab(a, r2);
+  } else if (t2 != TT_TAG_OK) {
+    return tt_grab(a, r1);
+  } else {
+    tt_node_ptr_t s = RET_IF_NO_PTR(tt_dictset_union(a, TT_OK_DICT(a,r1), TT_OK_DICT(a,r2)));
+    tt_node_ptr_t result = tt_cons_ok(a, s);
+    tt_drop(a, s);
+    return tt_grab(a, result);
   }
-
-  /* No need for tt_grab here - g has already done that for us */
-  return g(r1, r2);
 }
 
 tt_node_ptr_t tt_trie_union_map(tt_arena_t *a, tt_node_ptr_t r1, tt_node_ptr_t r2) {
-  tt_node_ptr_t f_union_map(void *f_context, tt_node_ptr_t r1, tt_node_ptr_t r2) {
-    tt_tag_t t1 = tt_ptr_tag(r1);
-    tt_tag_t t2 = tt_ptr_tag(r2);
-    if (t1 != TT_TAG_OK) {
-      /* t2 must be ok. */
-      return tt_grab(a, r2);
-    } else if (t2 != TT_TAG_OK) {
-      return tt_grab(a, r1);
-    } else {
-      tt_node_ptr_t s = RET_IF_NO_PTR(tt_dictset_union(a, TT_OK_DICT(a,r1), TT_OK_DICT(a,r2)));
-      tt_node_ptr_t result = tt_cons_ok(a, s);
-      tt_drop(a, s);
-      return tt_grab(a, result);
-    }
-  }
-  return tt_trie_combine(a, r1, r2, 1, 1, 1, 1, NULL, f_union_map);
+  return tt_trie_combine(a, r1, r2, 1, 1, 1, 1, a, f_union_map);
+}
+
+struct f_union_set_context {
+  tt_arena_t *a;
+  tt_node_ptr_t emptyset;
+};
+
+static tt_node_ptr_t f_union_set(void *f_context, tt_node_ptr_t r1, tt_node_ptr_t r2) {
+  struct f_union_set_context *c = (struct f_union_set_context *) f_context;
+  return tt_grab(c->a, c->emptyset);
 }
 
 tt_node_ptr_t tt_trie_union_set(tt_arena_t *a, tt_node_ptr_t r1, tt_node_ptr_t r2) {
-  tt_node_ptr_t emptyset = tt_grab(a, RET_IF_NO_PTR(tt_cons_ok(a, TT_EMPTY_DICT)));
+  struct f_union_set_context context;
   tt_node_ptr_t result;
-  tt_node_ptr_t f_union_map(void *f_context, tt_node_ptr_t r1, tt_node_ptr_t r2) {
-    return tt_grab(a, emptyset);
-  }
-  result = tt_trie_combine(a, r1, r2, 1, 1, 1, 1, NULL, f_union_map);
-  tt_drop(a, emptyset);
+  context.a = a;
+  context.emptyset = tt_grab(a, RET_IF_NO_PTR(tt_cons_ok(a, TT_EMPTY_DICT)));
+  result = tt_trie_combine(a, r1, r2, 1, 1, 1, 1, &context, f_union_set);
+  tt_drop(a, context.emptyset);
   return result;
 }
 
+static tt_node_ptr_t f_subtract_set(void *f_context, tt_node_ptr_t r1, tt_node_ptr_t r2) {
+  return TT_EMPTY;
+}
+
 tt_node_ptr_t tt_trie_subtract_set(tt_arena_t *a, tt_node_ptr_t r1, tt_node_ptr_t r2) {
-  tt_node_ptr_t f_subtract_set(void *f_context, tt_node_ptr_t r1, tt_node_ptr_t r2) {
-    return TT_EMPTY;
-  }
   return tt_trie_combine(a, r1, r2, 0, 1, 1, 0, NULL, f_subtract_set);
 }
 
@@ -365,59 +428,74 @@ tt_node_ptr_t tt_trie_step(tt_arena_t *a, tt_node_ptr_t r, tt_atom_t key) {
   }
 }
 
+struct tt_trie_relabel_visit_edge_context {
+  tt_arena_t *a;
+  void *f_context;
+  tt_node_ptr_t (*f)(void *f_context, tt_node_ptr_t oldlabel);
+  tt_node_ptr_t wild;
+  tt_node_ptr_t others;
+};
+
+static int tt_trie_relabel_visit_edge(void *context, tt_atom_t key, tt_node_ptr_t trie) {
+  struct tt_trie_relabel_visit_edge_context *c =
+    (struct tt_trie_relabel_visit_edge_context *) context;
+  tt_arena_t *a = c->a;
+  tt_node_ptr_t new_trie = tt_grab(a, tt_trie_relabel(a, trie, c->f_context, c->f));
+  tt_node_ptr_t new_others;
+  if (TT_NO_PTR_P(new_trie)) return 0;
+  new_others = tt_grab(a, rupdate_dict(a, c->wild, c->others, key, new_trie));
+  tt_drop(a, new_trie);
+  if (TT_NO_PTR_P(new_others)) return 0;
+  tt_drop(a, c->others);
+  c->others = new_others;
+  return 1;
+}
+
 tt_node_ptr_t tt_trie_relabel(tt_arena_t *a,
 			      tt_node_ptr_t r,
 			      void *f_context,
 			      tt_node_ptr_t (*f)(void *f_context,
 						 tt_node_ptr_t oldlabel))
 {
-  tt_node_ptr_t walk(tt_node_ptr_t r) {
-    if (TT_EMPTY_P(r)) {
-      return r;
-    }
-
-    switch (tt_ptr_tag(r)) {
-      case TT_TAG_OK:
-	return tt_cons_ok(a, RET_IF_NO_PTR(f(f_context, TT_OK_DICT(a, r))));
-
-      case TT_TAG_TAIL:
-	return tt_cons_tail(a, RET_IF_NO_PTR(walk(TT_TAIL_TRIE(a, r))));
-
-      case TT_TAG_BRANCH: {
-	tt_node_ptr_t wild = tt_grab(a, RET_IF_NO_PTR(walk(TT_BRANCH_WILDCARD(a, r))));
-	tt_node_ptr_t others = TT_EMPTY_DICT; /* grab'd */
-	tt_node_ptr_t result = TT_NO_PTR;
-	int visit_edge(void *context, tt_atom_t key, tt_node_ptr_t trie) {
-	  tt_node_ptr_t new_trie = tt_grab(a, walk(trie));
-	  tt_node_ptr_t new_others;
-	  if (TT_NO_PTR_P(new_trie)) return 0;
-	  new_others = tt_grab(a, rupdate_dict(a, wild, others, key, new_trie));
-	  tt_drop(a, new_trie);
-	  if (TT_NO_PTR_P(new_others)) return 0;
-	  tt_drop(a, others);
-	  others = new_others;
-	  return 1;
-	}
-	if (tt_dict_foreach(a, TT_BRANCH_OTHERS(a, r), NULL, visit_edge)) {
-	  result = rbranch(a, wild, others);
-	}
-	tt_drop(a, wild);
-	tt_drop(a, others);
-	return result;
-      }
-
-      default:
-	assert(0);
-    }
+  if (TT_EMPTY_P(r)) {
+    return r;
   }
-  return walk(r);
+
+  switch (tt_ptr_tag(r)) {
+    case TT_TAG_OK:
+      return tt_cons_ok(a, RET_IF_NO_PTR(f(f_context, TT_OK_DICT(a, r))));
+
+    case TT_TAG_TAIL:
+      return tt_cons_tail(a, RET_IF_NO_PTR(tt_trie_relabel(a, TT_TAIL_TRIE(a, r), f_context, f)));
+
+    case TT_TAG_BRANCH: {
+      struct tt_trie_relabel_visit_edge_context context;
+      context.a = a;
+      context.f_context = f_context;
+      context.f = f;
+      context.wild =
+	tt_grab(a, RET_IF_NO_PTR(tt_trie_relabel(a, TT_BRANCH_WILDCARD(a, r), f_context, f)));
+      context.others = TT_EMPTY_DICT; /* grab'd */
+      tt_node_ptr_t result = TT_NO_PTR;
+      if (tt_dict_foreach(a, TT_BRANCH_OTHERS(a, r), &context, tt_trie_relabel_visit_edge)) {
+	result = rbranch(a, context.wild, context.others);
+      }
+      tt_drop(a, context.wild);
+      tt_drop(a, context.others);
+      return result;
+    }
+
+    default:
+      assert(0);
+  }
+}
+
+static tt_node_ptr_t relabel_to_const(void *context, tt_node_ptr_t oldlabel) {
+  return *((tt_node_ptr_t *) context);
 }
 
 tt_node_ptr_t tt_trie_relabel_const(tt_arena_t *a, tt_node_ptr_t r, tt_node_ptr_t newlabel) {
-  tt_node_ptr_t relabel_to_const(void *context, tt_node_ptr_t oldlabel) {
-    return newlabel;
-  }
-  return tt_trie_relabel(a, r, NULL, relabel_to_const);
+  return tt_trie_relabel(a, r, &newlabel, relabel_to_const);
 }
 
 tt_node_ptr_t tt_begin_path(tt_arena_t *a, tt_node_ptr_t ok_dict) {
@@ -450,73 +528,91 @@ static size_t gross_approximate_utf8_strlen(char const *c) {
   return count;
 }
 
-void tt_dump_routingtable(tt_arena_t *a, tt_node_ptr_t r, int initial_indent) {
-  void walk(int indent, tt_node_ptr_t r) {
-    switch (tt_ptr_tag(r)) {
-      case TT_TAG_TAIL:
-	printf(" ...>");
-	walk(indent + 5, TT_TAIL_TRIE(a, r));
-	break;
-      case TT_TAG_OK: {
-	int need_space = 0;
-	int pkey(void *context, tt_atom_t key, tt_node_ptr_t ignored_trie) {
-	  if (need_space) {
-	    putchar(' ');
-	  } else {
-	    need_space = 1;
-	  }
-	  printf("%d", key);
-	  return 1;
-	}
-	fputs(" {", stdout);
-	tt_dict_foreach(a, TT_OK_DICT(a, r), NULL, pkey);
-	putchar('}');
-	break;
-      }
-      case TT_TAG_BRANCH: {
-	int need_sep = 0;
-	int pedge(void *context, tt_atom_t key, tt_node_ptr_t node) {
-	  char keystr[256]; /* not very tight */
-	  if (need_sep) {
-	    putchar('\n');
-	    print_indent(indent);
-	  } else {
-	    need_sep = 1;
-	  }
-	  keystr[sizeof(keystr) - 1] = '\0';
-	  switch (key) {
-	    case TT_WILD: snprintf(keystr, sizeof(keystr) - 1, " ★"); break;
-	    case TT_BOS: snprintf(keystr, sizeof(keystr) - 1, " <"); break;
-	    case TT_EOS: snprintf(keystr, sizeof(keystr) - 1, " >"); break;
-	    case TT_BOC: snprintf(keystr, sizeof(keystr) - 1, " {"); break;
-	    case TT_EOC: snprintf(keystr, sizeof(keystr) - 1, " }"); break;
-	    default:
-	      snprintf(keystr, sizeof(keystr) - 1, " %d", key);
-	  }
-	  fputs(keystr, stdout);
-	  walk(indent + gross_approximate_utf8_strlen(keystr), node);
-	  return 1;
-	}
-	if (!TT_EMPTY_P(TT_BRANCH_WILDCARD(a, r))) {
-	  pedge(NULL, TT_WILD, TT_BRANCH_WILDCARD(a, r));
-	}
-	tt_dict_foreach(a, TT_BRANCH_OTHERS(a, r), NULL, pedge);
-	if (!need_sep) {
-	  printf(" ::: no edges!");
-	}
-	break;
-      }
-      case TT_TAG_SPECIAL:
-	if (TT_EMPTY_P(r)) {
-	  printf(" ::: nothing");
-	  break;
-	}
-	/* fall through */
-      default:
-	printf("?!?!?! %x", (unsigned int) r);
-	break;
-    }
+static int tt_dump_routingtable_pkey(void *context, tt_atom_t key, tt_node_ptr_t ignored_trie) {
+  int *need_space = (int *) context;
+  if (*need_space) {
+    putchar(' ');
+  } else {
+    *need_space = 1;
   }
-  walk(initial_indent, r);
+  printf("%d", key);
+  return 1;
+}
+
+/* Forward declaration (mutual recursion) */
+static void tt_dump_routingtable_walk(tt_arena_t *a, tt_node_ptr_t r, int indent);
+
+struct tt_dump_routingtable_pedge_context {
+  tt_arena_t *a;
+  int indent;
+  int need_sep;
+};
+
+static int tt_dump_routingtable_pedge(void *context, tt_atom_t key, tt_node_ptr_t node) {
+  struct tt_dump_routingtable_pedge_context *c =
+    (struct tt_dump_routingtable_pedge_context *) context;
+  char keystr[256]; /* not very tight */
+  if (c->need_sep) {
+    putchar('\n');
+    print_indent(c->indent);
+  } else {
+    c->need_sep = 1;
+  }
+  keystr[sizeof(keystr) - 1] = '\0';
+  switch (key) {
+    case TT_WILD: snprintf(keystr, sizeof(keystr) - 1, " ★"); break;
+    case TT_BOS: snprintf(keystr, sizeof(keystr) - 1, " <"); break;
+    case TT_EOS: snprintf(keystr, sizeof(keystr) - 1, " >"); break;
+    case TT_BOC: snprintf(keystr, sizeof(keystr) - 1, " {"); break;
+    case TT_EOC: snprintf(keystr, sizeof(keystr) - 1, " }"); break;
+    default:
+      snprintf(keystr, sizeof(keystr) - 1, " %d", key);
+  }
+  fputs(keystr, stdout);
+  tt_dump_routingtable_walk(c->a, node, c->indent + gross_approximate_utf8_strlen(keystr));
+  return 1;
+}
+
+static void tt_dump_routingtable_walk(tt_arena_t *a, tt_node_ptr_t r, int indent) {
+  switch (tt_ptr_tag(r)) {
+    case TT_TAG_TAIL:
+      printf(" ...>");
+      tt_dump_routingtable_walk(a, TT_TAIL_TRIE(a, r), indent + 5);
+      break;
+    case TT_TAG_OK: {
+      int need_space = 0;
+      fputs(" {", stdout);
+      tt_dict_foreach(a, TT_OK_DICT(a, r), &need_space, tt_dump_routingtable_pkey);
+      putchar('}');
+      break;
+    }
+    case TT_TAG_BRANCH: {
+      struct tt_dump_routingtable_pedge_context context;
+      context.a = a;
+      context.indent = indent;
+      context.need_sep = 0;
+      if (!TT_EMPTY_P(TT_BRANCH_WILDCARD(a, r))) {
+	tt_dump_routingtable_pedge(&context, TT_WILD, TT_BRANCH_WILDCARD(a, r));
+      }
+      tt_dict_foreach(a, TT_BRANCH_OTHERS(a, r), &context, tt_dump_routingtable_pedge);
+      if (!context.need_sep) {
+	printf(" ::: no edges!");
+      }
+      break;
+    }
+    case TT_TAG_SPECIAL:
+      if (TT_EMPTY_P(r)) {
+	printf(" ::: nothing");
+	break;
+      }
+      /* fall through */
+    default:
+      printf("?!?!?! %x", (unsigned int) r);
+      break;
+  }
+}
+
+void tt_dump_routingtable(tt_arena_t *a, tt_node_ptr_t r, int initial_indent) {
+  tt_dump_routingtable_walk(a, r, initial_indent);
   putchar('\n');
 }