added explanatory comment

elmish · Oct 14, 2020 · d91c479 · d91c479
1 parent 67e84a3
commit d91c479
Showing 1 changed file with 9 additions and 1 deletion.
diff --git a/src/Samples/SubModelSeq/Program.fs b/src/Samples/SubModelSeq/Program.fs
@@ -47,7 +47,15 @@ module List =
   let mapFirst p f input =
     let rec mapFirstRec reverseFront back =
       match back with
-      | [] -> input
+      | [] ->
+          (*
+           * Conceptually, the correct value to return is
+           * reverseFront |> List.rev
+           * but this is the same as
+           * input
+           * so returning that instead.
+           *)
+          input
       | a :: ma ->
           if p a then
             (reverseFront |> List.rev) @ (f a :: ma)