begin adding tests for persistent-vector.sml, and add bug fix to 'PersistentVector.delete' in light of one of the tests. (We were decrementing by the wrong value previously, but I fixed it and added a comment of how we arrive at the value we want to decrement by

fcore/persistent-vector.sml

@@ -349,8 +349,16 @@ struct
 
   fun getMaxSize tree =
     case tree of
-      BRANCH (_, sizes) => Vector.sub (sizes, Vector.length sizes - 1)
-    | LEAF (_, sizes) => Vector.sub (sizes, Vector.length sizes - 1)
+      BRANCH (_, sizes) => 
+        if Vector.length sizes = 0 then
+          0
+        else
+          Vector.sub (sizes, Vector.length sizes - 1)
+    | LEAF (_, sizes) => 
+        if Vector.length sizes = 0 then
+          0
+        else
+          Vector.sub (sizes, Vector.length sizes - 1)
 
   fun splitLeft (offset, tree) =
     case tree of
@@ -893,7 +901,7 @@ struct
     fun delete (start, length, tree) =
       let
         val finishIdx = start + length
-        val {start, finish} = startNextMatch (finishIdx, tree)
+        val {start, finish} = startNextMatch (start, tree)
       in
         if start = ~1 then
           (* nothing to delete *)
@@ -902,19 +910,40 @@ struct
           let
             (* split left and right side *)
             val left = splitLeft (start, tree)
-            val left = root left
-
             val right = splitRight (finishIdx, tree)
+          in
+            if isEmpty right then
+              root left
+            else
+              let
+                val left = root left
                 val right = root right
 
                 (* calculate what the new index should be
                  * for the first match in the right tree,
                  * and decrement the right tree to reach this index
-             * if necessary. *)
+                 * if necessary. 
+                 *
+                 * We calculate the index the right node should start at
+                 * using this method:
+                 * 1. We get the first match after finishIdx from the original * tree
+                 * 2. We subtract this by the length provided to us,
+                 *    which tells us where the right node should start at.
+                 * 3. We get the first item in the right node,
+                 *    and add the last item in the left node 
+                 *    to get an absolute value.
+                 * 4. We subtract the match from the original tree
+                 *    by the first item in the right node.
+                 *    This step gives us the difference: how much
+                 *    we need to decrement the right node by.
+                 * *)
+                val {start = shouldBeStart, ...} = 
+                  startNextMatch (finishIdx, tree)
+                val shouldBeStart = shouldBeStart - length
+
                 val leftSize = getMaxSize left
                 val {start = rightStart, ...} = getFirstItem right
-            val rightStart = rightStart + leftSize
-            val difference = start - rightStart
+                val difference = rightStart - shouldBeStart
                 val right =
                   if difference = 0 then
                     right
@@ -924,6 +953,7 @@ struct
                 join (left, right)
               end
           end
+      end
 
   (* conversion functions for testing *)
   fun helpFromList ([], acc) = acc

shf-tests.mlb

@@ -71,4 +71,5 @@ test/test-utils.sml
 test/normal-move.sml
 test/normal-delete.sml
 test/regression.sml
+test/persistent-vector-tests.sml
 test/test.sml

test/persistent-vector-tests.sml

@@ -0,0 +1,55 @@
+structure PersistentVectorTests =
+struct
+  open Railroad
+  open Railroad.Test
+
+  structure Pv = PersistentVector
+
+  val appendTests = describe "PersistentVector.append"
+    [test "appends new values to end" (fn _ =>
+       let
+         (* arrange *)
+         val pv = Pv.fromList [(1, 1), (3, 3)]
+
+         (* act *)
+         val pv = Pv.append (5, 7, pv)
+
+         (* assert *)
+         val outputList = Pv.toList pv
+         val expectedList = [(1, 1), (3, 3), (5, 7)]
+       in
+         Expect.isTrue (outputList = expectedList)
+       end)]
+
+  fun printList lst =
+    let
+      val str =
+        List.map
+          (fn (start, finish) =>
+             "(" ^ Int.toString start ^ ", " ^ Int.toString finish ^ ")") lst
+      val str = "[" ^ String.concatWith ", " str ^ "]\n"
+    in
+      print str
+    end
+
+  val deleteTests = describe "PersistentVector.delete"
+    [test
+       "deletes last value correctly \
+       \when only last value is in deletion range"
+       (fn _ =>
+          let
+            (* arrange *)
+            val pv = Pv.fromList [(0, 0), (3, 3), (5, 5)]
+
+            (* act *)
+            val pv = Pv.delete (5, 1, pv)
+
+            (* assert *)
+            val outputList = Pv.toList pv
+            val expectedList = [(0, 0), (3, 3)]
+          in
+            Expect.isTrue (outputList = expectedList)
+          end)]
+
+  val tests = [appendTests, deleteTests]
+end

test/test.sml

@@ -5,12 +5,12 @@ struct
 
   fun main () =
     let
-      val tests =
-        List.concat
+      val tests = List.concat
         [ NormalMove.tests
         , NormalDelete.tests
         , Regression.tests
         , RegexTests.tests
+        , PersistentVectorTests.tests
         ]
       val tests = concat tests
     in