From 1c947eab7d1a07a2ceff108fbfd31f158cdbfb57 Mon Sep 17 00:00:00 2001
From: Humza Shahid <humzasaur@gmail.com>
Date: Sat, 17 Jan 2026 23:27:36 +0000
Subject: [PATCH] add a test for 'PersistentVector.delete' (even though the
 'PersistentVector.merge' helper function is unimplemented)

---
 fcore/persistent-vector.sml      |  4 ++--
 test/persistent-vector-tests.sml | 36 +++++++++++++++++++++++++++++++-
 2 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/fcore/persistent-vector.sml b/fcore/persistent-vector.sml
index f16f0e3..83cf069 100644
--- a/fcore/persistent-vector.sml
+++ b/fcore/persistent-vector.sml
@@ -550,9 +550,9 @@ struct
   fun delete (start, finish, tree) =
     let
       val matchAfterFinish = nextMatch (finish, tree, 1)
-      val left = splitRight (start, tree)
+      val left = splitLeft (start, tree)
     in
-      if  matchAfterFinish = ~1 then
+      if matchAfterFinish = ~1 then
         (* there is no match after 'finish', so just split left. 
          * No need to decrement or split right, 
          * because the right vector would be empty. *)
diff --git a/test/persistent-vector-tests.sml b/test/persistent-vector-tests.sml
index de74e4e..a3d05ad 100644
--- a/test/persistent-vector-tests.sml
+++ b/test/persistent-vector-tests.sml
@@ -284,5 +284,39 @@ struct
            end)
     ]
 
-  val tests = [appendTests, toListTests, splitLeftTests]
+  val deleteTests = describe "PersistentVector.delete"
+    [test
+       "returns the left side of the vector \
+       \when 'finish' is greater than any element in the vector"
+       (fn _ =>
+          let
+            (* arrange *)
+            val inputList =
+              [ {start = 1, finish = 1}
+              , {start = 2, finish = 2}
+              , {start = 3, finish = 3}
+              , {start = 4, finish = 4}
+              , {start = 5, finish = 5}
+              , {start = 6, finish = 6}
+              , {start = 7, finish = 7}
+              , {start = 8, finish = 8}
+              ]
+            val pv = PersistentVector.fromList inputList
+
+            (* act *)
+            val pv = PersistentVector.delete (5, 9, pv)
+
+            (* assert *)
+            val outputList = PersistentVector.toList pv
+            val expectedOutput =
+              [ {start = 1, finish = 1}
+              , {start = 2, finish = 2}
+              , {start = 3, finish = 3}
+              , {start = 4, finish = 4}
+              ]
+          in
+            Expect.isTrue (outputList = expectedOutput)
+          end)]
+
+  val tests = [appendTests, toListTests, splitLeftTests, deleteTests]
 end