Add more helpers to Fantomas library (#7)

WoofWare.Whippet.Fantomas/List.fs

@@ -0,0 +1,23 @@
+namespace WoofWare.Whippet.Fantomas
+
+[<RequireQualifiedAccess>]
+module private List =
+    let partitionChoice<'a, 'b> (xs : Choice<'a, 'b> list) : 'a list * 'b list =
+        let xs, ys =
+            (([], []), xs)
+            ||> List.fold (fun (xs, ys) v ->
+                match v with
+                | Choice1Of2 x -> x :: xs, ys
+                | Choice2Of2 y -> xs, y :: ys
+            )
+
+        List.rev xs, List.rev ys
+
+    let allSome<'a> (l : 'a option list) : 'a list option =
+        let rec go acc (l : 'a option list) =
+            match l with
+            | [] -> Some (List.rev acc)
+            | None :: _ -> None
+            | Some head :: tail -> go (head :: acc) tail
+
+        go [] l