a bit of formatting (code does same thing, but is expressed in a way that is a little clearer after the formatter has been run)

fcore/layer-tree.sml

@@ -17,13 +17,19 @@ struct
       LEAF => NODE {key = newKey, value = newValue, left = LEAF, right = LEAF}
     | NODE {key, value, left, right} =>
         if newKey < key then
-          let val left = insert (newKey, newValue, left)
-          in NODE {key = key, value = value, left = left, right = right}
-          end
+          NODE
+            { key = key
+            , value = value
+            , left = insert (newKey, newValue, left)
+            , right = right
+            }
         else if newKey > key then
-          let val right = insert (newKey, newValue, right)
-          in NODE {key = key, value = value, left = left, right = right}
-          end
+          NODE
+            { key = key
+            , value = value
+            , left = left
+            , right = insert (newKey, newValue, right)
+            }
         else
           NODE {key = key, value = newValue, left = left, right = right}