add delete function to rope.sml

rope.sml

@@ -4,6 +4,7 @@ signature ROPE = sig
   val of_string : string -> t
   val size : t -> int
   val insert : int * string * t -> t
+  val delete : int * int * t -> t
 end
 
 structure Rope :> ROPE = struct
@@ -28,7 +29,6 @@ structure Rope :> ROPE = struct
 
   exception AuxConstructor
 
-  local
   fun help_size(acc, rope) =
     case rope of
       N0 s => 
@@ -38,9 +38,8 @@ structure Rope :> ROPE = struct
     | N2(_, lm, r) =>
         help_size(acc + lm, r)
     | _ => raise AuxConstructor
-  in
+
   fun size rope = help_size(0, rope)
-  end
 
   fun ins_root rope =
     case rope of
@@ -177,7 +176,6 @@ structure Rope :> ROPE = struct
     | (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
@@ -205,6 +203,7 @@ structure Rope :> ROPE = struct
           else
             (N3(N0 sub1, N0 new_str, N0 sub2), AddedNode)
         end
+
   fun ins(cur_index, new_str, rope) =
     case rope of
       N2(l, lm, r) =>
@@ -260,7 +259,7 @@ structure Rope :> ROPE = struct
         ins_leaf(cur_index, new_str, rope, old_str)
     | _ =>
         raise AuxConstructor
-   in
+ 
   fun insert (index, str, rope) =
     let
       val (rope, action) = ins(index, str, rope)
@@ -273,5 +272,85 @@ structure Rope :> ROPE = struct
       | DeletedNode =>
           del_root rope)
     end
+
+  fun del_leaf(start_idx, end_idx, str) =
+    if start_idx <= 0 andalso end_idx >= String.size str then
+      (empty, false)
+    else if start_idx >= 0 andalso end_idx <= String.size str then
+      let
+        val sub1 = String.substring(str, 0, start_idx)
+        val sub2 = String.substring(str, end_idx, (String.size str - end_idx))
+      in
+        if start_idx + (String.size str - end_idx) <= target_length then
+          (N0 (sub1 ^ sub2), false)
+        else
+          (L2(sub1, sub2), true)
+      end
+    else if start_idx >= 0 andalso end_idx >= String.size str then
+      let
+        val str = String.substring(str, 0, start_idx)
+      in
+        (N0 str, false)
+      end
+    else
+      let
+        val str = String.substring(str, end_idx, String.size str - end_idx)
+      in
+        (N0 str, false)
+      end
+
+  fun del (start_idx, end_idx, rope) =
+    case rope of
+      N2(l, lm, r) =>
+        if lm > start_idx andalso lm > end_idx then
+          let
+            val (l, did_add) = del(start_idx, end_idx, l)
+          in
+            if did_add then 
+              (ins_n2_left(l, r), did_add)
+            else
+              (N2(l, size l, r), did_add)
+          end
+        else if lm < start_idx andalso lm < end_idx then
+          let
+            val (r, did_add) = del(start_idx - lm, end_idx - lm, r)
+          in
+            if did_add then
+              (ins_n2_right(l, r), did_add)
+            else
+              (N2(l, lm, r), did_add)
+          end
+        else
+          let
+            val (l, did_add_l) = del(start_idx, end_idx, l)
+            val (r, did_add_r) = del(start_idx - lm, end_idx - lm, r)
+          in
+            if did_add_l then
+              (ins_n2_left(l, r), did_add_l)
+            else if did_add_r then
+              (ins_n2_right(l, r), did_add_r)
+            else
+              (N2(l, size l, r), false)
+          end
+    | N1 t =>
+        let
+          val (t, did_add) = del(start_idx, end_idx, t)
+        in
+          if did_add then
+            (ins_n1 t, did_add)
+          else
+            (N1 t, did_add)
+        end
+    | N0 str =>
+        del_leaf(start_idx, end_idx, str)
+
+  fun delete(start, length, rope) =
+    let
+      val (rope, did_add) = del(start, start + length, rope)
+    in
+      if did_add then
+        ins_root rope
+      else
+        del_root rope
     end
 end

utils.sml

@@ -21,12 +21,12 @@ fun run_txns arr =
       let
         val rope = 
           if del_num > 0 
-          then delete pos del_num rope 
+          then Rope.delete(pos, del_num, rope)
           else rope
         val str_size = String.size ins_str
         val rope = 
           if str_size > 0 
-          then insert pos ins_str rope 
+          then Rope.insert(pos, ins_str, rope)
           else rope
       in
         rope