finish initial implementation for 'PersistentVector.splitRight'

fcore/persistent-vector.sml

@@ -364,6 +364,9 @@ struct
                 end
             end
      | BRANCH (nodes, sizes) =>
+         if Vector.length nodes = 0 then
+           tree
+         else 
            if splitIdx < Vector.sub (sizes, 0) then
              (* we want to split first node from rest *)
              splitLeft (splitIdx, Vector.sub (nodes, 0))
@@ -462,6 +465,40 @@ struct
                 BRANCH (nodes, sizes)
               end
           end
+    | LEAF (items, sizes) =>
+        if Vector.length items = 0 then
+          tree
+        else
+          if splitIdx > Vector.sub (sizes, Vector.length sizes - 1) then
+            empty
+          else if splitIdx < Vector.sub (sizes, 0) then
+            tree
+          else
+            let
+              val idx = BinSearch.equalOrMore (splitIdx, sizes)
+              val {start, finish} = Vector.sub (items, idx)
+              val idx =
+                if splitIdx >= start then
+                  idx + 1
+                else
+                  idx
+            in
+              if idx >= Vector.length items then
+                empty
+              else
+                let
+                  val len = Vector.length items - idx
+                  val itemsSlice = VectorSlice.slice (items, idx, SOME len)
+                  val items = VectorSlice.map 
+                    (fn {start, finish} => 
+                      {start = start - splitIdx, finish = finish - splitIdx}
+                    ) 
+                    itemsSlice
+                  val sizes = Vector.map #finish items
+                in
+                  LEAF (items, sizes)
+                end
+            end
 
   (* functions only for testing *)
   fun fromListLoop (lst, acc) =