added Tree.scan and then used it to implement calculateMoves

FSharp/ArchivePictures/Archive.fs

@@ -23,10 +23,6 @@ module Archive =
     let calculateMoves =
         let replaceDirectory (f : FileInfo) d =
             FileInfo (Path.Combine (d, f.Name))
-        let rec imp path = function
-            | Leaf x ->
-                Leaf { Source = x; Destination = replaceDirectory x path }
-            | Node (x, xs) ->
-                let newNPath = Path.Combine (path, x)
-                Tree.node newNPath (List.map (imp newNPath) xs)
-        imp ""
+        let leaf x path = { Source = x; Destination = replaceDirectory x path }
+        let node x path = Path.Combine (path, x)
+        Tree.scan node leaf ""

FSharp/ArchivePictures/Tree.fs

@@ -7,6 +7,12 @@ module Tree =
 
     let node x xs = Node (x, xs)
 
+    let rec scan f g z = function
+        | Leaf x -> g x z |> leaf
+        | Node (x, xs) ->
+            let z' = f x z
+            xs |> List.map (scan f g z') |> node z'
+
     let rec cata fd ff = function
         | Leaf x -> ff x
         | Node (x, xs) -> xs |> List.map (cata fd ff) |> fd x