diff --git a/.DS_Store b/.DS_Store
index 6308708..13aadb5 100644
Binary files a/.DS_Store and b/.DS_Store differ
diff --git a/.rope.sml.swp b/.rope.sml.swp
new file mode 100644
index 0000000..38d7d93
Binary files /dev/null and b/.rope.sml.swp differ
diff --git a/mlton b/mlton
new file mode 160000
index 0000000..fd6d870
--- /dev/null
+++ b/mlton
@@ -0,0 +1 @@
+Subproject commit fd6d8705780ea6e223c91a6b33553be1633c4eab
diff --git a/rope.sml b/rope.sml
index 218c9eb..fec75bb 100644
--- a/rope.sml
+++ b/rope.sml
@@ -1,398 +1,277 @@
-datatype rope = 
-  N0 of string
-  | N1 of rope
-  | N2 of rope * int * int * rope
-  | L2 of string * string
-  | N3 of rope * rope * rope
+signature ROPE = sig
+  type t
+  val empty : t
+  val of_string : string -> t
+  val size : t -> int
+  val insert : int * string * t -> t
+end
 
-val target_length = 1024
-val empty = N0 ""
-fun of_string string = N0 string
+structure Rope :> ROPE = struct
+  datatype t  
+    = N0 of string
+    | N1 of t
+    | N2 of t * int * t
+    | L2 of string * string
+    | N3 of t * t * t
 
-exception Size
-exception Ins
-exception Substring
-exception Delete
-exception To_string
+  datatype balance  
+    = AddedNode
+    | DeletedNode
+    | NoAction
 
-fun size rope = 
-   case rope of
-   N0 s => String.size s
-   | N1 t => size t
-   | N2(_, lm, rm, _) => lm + rm
-   | N3(t1, t2, t3) => 
-      let
-        val t1_size = size t1
-        val t2_size = size t2
-        val t3_size = size t3
-      in
-        t1_size + t2_size + t3_size
-      end
-  | _ => raise Size
+  val target_length = 1024
+  val empty = N0 ""
+  fun of_string string = N0 string
 
-fun root rope =
-  case rope of
-    L2(s1, s2) => N2(N0 s1, String.size s1, String.size s2, N0 s2)
-  | N3(t1, t2, t3) =>
-    let
-      val t1_size = size t1
-      val t2_size = size t2
-      val left = N2(t1, t1_size, t2_size, t2)
-      val left_size = t1_size + t2_size
-      val t3_size = size t3
-    in
-      N2(left, left_size, t3_size, N1 t3)
-    end
-  | t => t
+  fun is_less_than_target(str1, str2) =
+    String.size str1 + String.size str2 <= target_length
 
-fun n1 rope = 
-  case rope of
-    L2(s1, s2) => 
-      N2(N0 s1, String.size s1, String.size s2, N0 s2)
-  | N3(t1, t2, t3) =>
-      let
-        val t1_size = size t1
-        val t2_size = size t2
-        val left = N2(t1, t1_size, t2_size, t2)
-        val left_size = t1_size + t2_size
-        val t3_size = size t3
-      in
-        N2(left, left_size, t3_size, N1 t3)
-      end
-  | t => N1 t
+  exception AuxConstructor
 
-fun ins_n2_left left right = 
-  case (left, right) of
-    (L2(s1, s2), t3) => N3(N0 s1, N0 s2, t3)
-  | (N3(t1, t2, t3), N1 t4) =>
-      let
-        val t1_size = size t1
-        val t2_size = size t2 
-        val left = N2(t1, t1_size, t2_size, t2)
-        val left_size = t1_size + t2_size
-        val t3_size = size t3
-        val t4_size = size t4
-        val right = N2(t3, t3_size, t4_size, t4)
-        val right_size = t3_size + t4_size
-      in
-        N2(left, left_size, right_size, right)
-      end
-  | (N3(t1, t2, t3), t4 as N2 _) =>
-      let
-        val left = N2(t1, size t1, size t2, t2)
-      in
-        N3(left, N1 t3, t4)
-      end
-  | (N3(t1, t2, t3), t4) =>
-      let
-        val t1_size = size t1
-        val t2_size = size t2
-        val left = N2(t1, t1_size, t2_size, t2)
-        val t3_size = size t3
-        val t4_size = size t4
-        val right = N2(t3, t3_size, t4_size, t4)
-        val left_size = t1_size + t2_size
-        val right_size = t3_size + t4_size
-      in
-        N2(left, left_size, right_size, right)
-      end
-  | (l, r) =>
-      N2(l, size l, size r, r)
+  local
+    fun help_size(acc, rope) =
+      case rope of
+        N0 s => 
+          acc + String.size s
+      | N1 t => 
+          help_size(acc, t)
+      | N2(_, lm, r) =>
+          help_size(acc + lm, r)
+      | _ => raise AuxConstructor
+  in
+    fun size rope = help_size(0, rope)
+  end
 
-fun ins_n2_right left right =
-  case (left, right) of
-    (t1, L2(s1, s2)) => N3(t1, N0 s1, N0 s2)
-  | (N1 t1, N3(t2, t3, t4)) =>
-      let
-        val t1_size = size t1
-        val t2_size = size t2
-        val left = N2(t1, t1_size, t2_size, t2)
-        val t3_size = size t3
-        val t4_size = size t4
-        val right = N2(t3, t3_size, t4_size, t4)
-        val right_size = t3_size + t4_size
-        val left_size = t1_size + t2_size
-      in
-        N2(left, left_size, right_size, right)
-      end
-  | (t1 as N2 _, N3(t2, t3, t4)) =>
-      let
-        val right = N2(t3, size t3, size t4, t4)
-      in
-        N3(t1, N1 t2, right)
-      end
-  | (t1, N3(t2, t3, t4)) =>
-      let
-        val t1_size = size t1
-        val t2_size = size t2
-        val left = N2(t1, t1_size, t2_size, t2)
-        val t3_size = size t3
-        val t4_size = size t4
-        val right = N2(t3, t3_size, t4_size, t4)
-        val right_size = t3_size + t4_size
-        val left_size = t1_size + t2_size
-      in
-        N2(left, left_size, right_size, right)
-      end
-  | (l, r) =>
-      N2(l, size l, size r, r)
-
-fun ins cur_index string rope =
-  case rope of
-    N0 str =>
-      let
-        val old_str_size = String.size str 
-        val ins_str_size = String.size string
-        val total_str_size = old_str_size + ins_str_size
-        val left_size = ins_str_size + cur_index
-        val prefer_left = left_size <= target_length
-        val right_size = ins_str_size - cur_index
-        val prefer_right = right_size <= target_length
-      in
-        if cur_index <= 0 then
-            if total_str_size <= target_length then
-              N0(string ^ str)
-            else L2(string, str)
-        else if cur_index >= old_str_size then
-            if total_str_size <= target_length then
-              N0(str ^ string)
-            else L2(str, string)
-        else if total_str_size <= target_length then
-            let
-              val str1 = String.substring(str, 0, cur_index)
-              val str3 = String.substring(str, cur_index, old_str_size - cur_index)
-            in
-              N0(String.concat [str1, string, str3])
-            end
-        else 
-            let
-              val str1 = String.substring(str, 0, cur_index)
-              val str3 = String.substring(str, cur_index, old_str_size - cur_index)
-            in
-              if prefer_left then
-                L2(str1 ^ string, str3)
-              else if prefer_right then
-                L2(str1, string ^ str3)
-              else
-                N3(N0 str1, N0 string, N0 str3)
-            end
-      end
-    | N1 t =>
+  fun ins_root rope =
+    case rope of
+      L2(s1, s2) => 
+        N2(N0 s1, String.size s1, N0 s2)
+    | N3(t1, t2, t3) =>
         let
-          val t = ins cur_index string t
+          val t1_size = size t1
+          val left = N2(t1, t1_size, t2)
+          val t2_size = size t2
         in
-          n1 t
+          N2(left, t1_size + t2_size, N1 t3)
         end
-    | N2(l, lm, _, r) =>
-        if cur_index < lm then
-          let
-            val l = ins cur_index string l
-          in
-            ins_n2_left l r
-          end
-        else
+    | t =>
+        N1 t
+
+  fun del_root rope =
+    case rope of
+      N1 t => t
+    | t => t
+
+  fun ins_n1 rope =
+    case rope of
+        L2 (s1, s2) =>
+          N2(N0 s1, String.size s1, N0 s2)
+      | N3(t1, t2, t3) =>
           let 
-            val next_index = cur_index - lm
-            val r = ins next_index string r
+            val left = N2(t1, size t1, t2)
           in
-            ins_n2_right l r
+            N2(left, size left, t2)
           end
-    | _ => raise Ins
+      | t =>
+          N1 t
 
-fun insert index string rope =
-  let
-    val rope = ins index string rope
-  in
-    root rope
-  end
+  fun ins_n2_left (left, right) =
+    case (left, right) of
+      (L2(s1, s2), t3) =>
+        N3(N0 s1, N0 s2, t3)
+    | (N3(t1, t2, t3), N1 t4) =>
+        let
+          val t1_size = size t1
+          val left = N2(t1, t1_size, t2)
+          val t3_size = size t3
+          val right = N2(t3, t3_size, t4)
+          val t2_size = size t2
+          val left_size = t1_size + t2_size
+        in
+          N2(left, left_size, right)
+        end
+    | (N3(t1, t2, t3), t4) =>
+        let 
+          val left = N2(t1, size t2, t2)
+        in
+          N3(left, N1 t3, t4)
+        end
+    | (l, r) =>
+        N2(l, size l, r)
 
-fun sub start_idx end_idx acc rope =
-  case rope of
-    N0 str =>
-      let 
-        val str_size = String.size str
-        val before_start = start_idx <= 0
-        val after_start = start_idx >= 0
-        val after_end = end_idx >= str_size
-        val before_end = end_idx <= str_size
-      in
-        if before_start andalso after_end then
-          (str :: acc)
-        else if after_start andalso before_start then
-          let
-            val len = end_idx - start_idx
-            val str = String.substring(str, start_idx, len)
-          in
-            (str :: acc)
-          end
-        else if after_start andalso after_end then
-          let
-            val len = str_size - start_idx
-            val str = String.substring(str, start_idx, len)
-          in
-            (str :: acc)
-          end
+  fun del_n2_left(left, right) = 
+    case (left, right) of
+      (N1 t1, N1 t2) =>
+        N1(N2(t1, size t1, t2))
+    | (N1 (N1 t1), N2(N1 t2, _, (t3 as N2 _))) =>
+        let
+          val left = N2(t1, size t1, t2)
+          val inner = N2(left, size left, t3)
+        in
+          N1 (inner)
+        end
+    | (N1 (N1 t1), N2(N2(t2, _, t3), _, N1 t4)) =>
+        let
+          val left = N2(t1, size t1, t2)
+          val right = N2(t3, size t3, t4)
+          val inner = N2(left, size left, right)
+        in
+          N1 inner
+        end
+    | (N1 (t1 as N1 _), N2((t2 as N2 _), _, (t3 as N2 _))) =>
+        let
+          val left = N2(t1, size t1, t2)
+          val right = N1 t3
+        in
+          N2(left, size left, right)
+        end
+    | (l, r) =>
+        N2(l, size l, r)
+
+  fun ins_n2_right (left, right) =
+    case (left, right) of
+      (t1, L2(s1, s2)) =>
+        N3(t1, N0 s1, N0 s2)
+    | (N1 t1, N3(t2, t3, t4)) =>
+        let
+          val left = N2(t1, size t1, t2)
+          val t3_size = size t3
+          val right = N2(t3, t3_size, t4)
+        in
+          N2(left, size left, right)
+        end
+    | (t1, N3(t2, t3, t4)) =>
+        let
+          val right = N2(t3, size t3, t4)
+        in
+          N3(t1, N1 t2, right)
+        end
+    | (l, r) =>
+        N2(l, size l, r)
+
+  fun del_n2_right(left, right) =
+    case (left, right) of
+      (N2(N1 t1, _, N2(t2, _, t3)), N1 t4) =>
+        let
+          val left = N2(t1, size t1, t2)
+          val right = N2(t3, size t3, t4)
+          val inner = N2(left, size left, right)
+        in
+          N1 inner
+        end
+    | (N2((t1 as N2 _), lm, N1 t2), N1 (N1 t3)) =>
+        let
+          val right = N2(t2, size t2, t3)
+          val inner = N2(t1, lm, right)
+        in
+          N1 inner
+        end
+    | (N2( (t1 as N2 _), _, (t2 as N2 _)), N1 (N1 t3)) =>
+        let
+          val left_size = size t1
+          val left = N1 t1
+          val right = N2(t2, size t2, t3)
+        in
+          N2(left, left_size, right)
+        end
+    | (l, r) =>
+        N2(l, size l, r)
+
+  local
+    fun ins_leaf(cur_index, new_str, rope, old_str) =
+      if cur_index <= 0 then
+        if is_less_than_target(old_str, new_str) then
+          (N0(new_str ^ old_str), NoAction)
         else
-          let
-            val str = String.substring(str, 0, end_idx)
-          in
-            (str::acc)
-          end
-      end
-    | N1 t =>
-        sub start_idx end_idx acc t
-    | N2(l, lm, _, r) =>
+          (L2(new_str, old_str), AddedNode)
+      else if cur_index >= String.size old_str then
+        if is_less_than_target(old_str, new_str) then
+          (N0(old_str ^ new_str), NoAction)
+        else
+          (L2(old_str, new_str), AddedNode)
+      else
+        (* Need to split in middle of string. *)
         let
-          val starts_before = lm > start_idx
-          val ends_before = lm > end_idx
-          val starts_after = lm < start_idx
-          val ends_after = lm < end_idx
+          val sub1 = String.substring(old_str, 0, cur_index)
+          val sub2_len = String.size old_str - cur_index
+          val sub2 = String.substring(old_str, cur_index, sub2_len)
         in
-          if starts_before andalso ends_before then
-            sub start_idx end_idx acc l
-          else if starts_after andalso ends_after then
-            let
-              val next_start = start_idx - lm
-              val next_end = end_idx - lm
-            in
-              sub next_start next_end acc r
-            end
+          if is_less_than_target(old_str, new_str) then
+            (N0(sub1 ^ new_str ^ sub2), NoAction)
+          else if cur_index + String.size new_str <= target_length then
+            (L2(sub1 ^ new_str, sub2), AddedNode)
+          else if (String.size old_str - cur_index) + String.size new_str <= target_length then
+            (L2(sub1, new_str ^ sub2), AddedNode)
           else
-            let
-              val next_start = start_idx - lm
-              val next_end = end_idx - lm
-              val sub_acc = sub next_start next_end acc r
-            in
-              sub start_idx end_idx sub_acc l
-            end
+            (N3(N0 sub1, N0 new_str, N0 sub2), AddedNode)
         end
-    | _ => raise Substring
-
-fun substring start length rope =
-  let
-    val finish = start + length
-    val lst = sub start finish [] rope
-  in
-    String.concat lst
-  end
-
-fun del start_idx end_idx rope =
-  case rope of
-    N0 str =>
-        let
-          val str_size = String.size str
-          val before_start = start_idx <= 0
-          val after_end = end_idx >= str_size
-          val after_start = start_idx >= 0
-          val before_end = end_idx <= str_size
-        in
-          if before_start andalso after_end then
-            (N0 "", false)
-          else if after_start andalso before_end then
-            let
-              val str1 = String.substring(str, 0, start_idx)
-              val del_len = str_size - end_idx
-              val str2 = String.substring(str, start_idx, del_len)
-              val new_len = str_size - del_len
-            in
-              if new_len <= target_length then
-                (N0(str1 ^ str2), false)
-              else
-                (L2(str1, str2), true)
-            end
-          else if after_start andalso after_end then
-            let
-              val str = String.substring(str, 0, start_idx)
-            in
-              (N0 str, false)
-            end
-          else
+    fun ins(cur_index, new_str, rope) =
+      case rope of
+        N2(l, lm, r) =>
+          if cur_index < lm then
             let 
-              val len = str_size - end_idx
-              val str = String.substring(str, end_idx, len)
+              val (l, action) = ins(cur_index, new_str, l)
             in
-              (N0 str, false)
-            end
-        end
-    | N1 t =>
-        let
-          val (t, did_ins) = del start_idx end_idx t 
-          val t = if did_ins then n1 t else t
-        in
-          (t, did_ins)
-        end
-    | N2(l, lm, rm, r) =>
-        let
-          val start_is_less = lm > start_idx
-          val end_is_less = lm > end_idx
-          val start_is_more = lm < start_idx
-          val end_is_more = lm < end_idx
-        in
-          if start_is_less andalso end_is_less then
-            let
-              val (l, did_ins) = del start_idx end_idx l
-            in
-              case did_ins of
-                false =>
-                  (N2(l, size l, rm, r), false)
-              | true =>
-                  (ins_n2_left l r, true)
-            end
-          else if start_is_more andalso end_is_more then
-            let
-              val next_start = start_idx - lm
-              val next_end = end_idx - lm
-              val (r, did_ins) = del next_start next_end r
-            in
-              case did_ins of
-                  false =>
-                    (N2(l, lm, size r, r), false)
-                | true =>
-                    (ins_n2_right l r, true)
+              (case action of
+                NoAction => 
+                  (case (l, r) of
+                    (N0 s1, N0 s2) =>
+                      if is_less_than_target(s1, s2) then
+                        (N0 (s1 ^ s2), DeletedNode)
+                      else
+                        (N2(l, lm + String.size new_str, r), action)
+                  | _ =>
+                    (N2(l, lm + String.size new_str, r), action))
+              | AddedNode =>
+                  (ins_n2_left(l, r), action)
+              | DeletedNode =>
+                  (del_n2_left(l, r), action))
             end
           else
             let
-              val (l, did_ins_l) = del start_idx end_idx l
-              val r_start = start_idx - lm
-              val r_end = end_idx - lm
-              val (r, did_ins_r) = del r_start r_end r
+              val (r, action) = ins(cur_index - lm, new_str, r)
             in
-              if did_ins_l then
-                (ins_n2_left l r, true)
-              else if did_ins_r then
-                (ins_n2_right l r, true)
-              else 
-                (N2(l, size l, size r, r), false)
+              (case action of
+                NoAction =>
+                  (case (l, r) of
+                    (N0 s1, N0 s2) =>
+                      if is_less_than_target(s1, s2) then
+                        (N0 (s1 ^ s2), DeletedNode)
+                      else
+                        (N2(l, lm, r), action)
+                    | _ =>
+                        (N2(l, lm, r), action))
+                | AddedNode =>
+                    (ins_n2_right(l, r), action)
+                | DeletedNode =>
+                    (del_n2_right(l, r), action))
             end
-        end
-    | _ => raise Delete
-
-fun delete start length rope =
-  let
-    val finish = start + length
-    val (t, did_ins) = del start finish rope
-    val t = if did_ins then root rope else rope
-  in
-    t
-  end
-
-fun to_str acc rope =
-  case rope of
-    N0 str =>
-      (str::acc)
-  | N1 t => 
-      to_str acc t
-  | N2 (l, _, _, r) =>
+      | N1 t =>
+          let
+            val (t, action) = ins(cur_index, new_str, t)
+          in
+            (case action of
+              AddedNode =>
+                (ins_n1 t, action)
+            | _ =>
+                (N1 t, action))
+          end
+      | N0 old_str => 
+          ins_leaf(cur_index, new_str, rope, old_str)
+      | _ =>
+          raise AuxConstructor
+   in
+    fun insert (index, str, rope) =
       let
-        val acc = to_str acc r
+        val (rope, action) = ins(index, str, rope)
       in
-        to_str acc l
+        (case action of
+          NoAction =>
+            rope
+        | AddedNode =>
+            ins_root rope
+        | DeletedNode =>
+            del_root rope)
       end
-  | _ => raise To_string
-
-fun to_string rope =
-  let
-    val lst = to_str [] rope
-  in
-    String.concat lst
   end
+end
diff --git a/utils.sml b/utils.sml
index 726869b..a1cf381 100644
--- a/utils.sml
+++ b/utils.sml
@@ -50,9 +50,15 @@ fun run_to_string_time title rope =
     time_func title f
   end
 
-fun run_txns_1000_times counter arr acc =
+fun run_txns_1000_times (counter, arr, total) =
   if counter = 1000 then
-    acc
+    let
+      val divisor = Int.toLarge 1000
+      val total = total div divisor
+      val str = LargeInt.toString total
+    in
+      print str
+    end
   else
     let
       val start_time = Time.now()
@@ -63,9 +69,10 @@ fun run_txns_1000_times counter arr acc =
       val end_time = Time.now()
       val end_time = Time.toMilliseconds end_time
       val time_diff = end_time - start_time 
-      val time_diff = LargeInt.toString time_diff
+      val counter = counter + 1
+      val total = time_diff + total
     in
-      run_txns_1000_times (counter + 1) arr (time_diff::acc)
+      run_txns_1000_times (counter, arr, total)
     end
 
 fun write_file filename acc =
@@ -80,17 +87,14 @@ fun write_file filename acc =
 
 val _ =
   let
-    val svelte = run_txns_1000_times 0 svelte_arr []
-    val _ = write_file "svelte_edit_traces.csv" svelte
+    val start_time = LargeInt.fromInt 0
+    val svelte = run_txns_1000_times (999 ,svelte_arr, start_time )
 
-    val rust = run_txns_1000_times 0 rust_arr []
-    val _ = write_file "rust_edit_traces.csv" rust
+    val rust = run_txns_1000_times (999 ,rust_arr, start_time )
 
-    val seph = run_txns_1000_times 0 seph_arr []
-    val _ = write_file "seph_edit_traces.csv" seph
+    val seph = run_txns_1000_times (999, seph_arr, start_time)
 
-    val automerge = run_txns_1000_times 0 automerge_arr []
-    val _ = write_file "automerge_edit_traces.csv" automerge
+    val automerge = run_txns_1000_times (999, automerge_arr , start_time)
   in
     ()
   end