anchor.diff:      // Call the function which traverses the pattern to validate/preprocess it.
       validateAndSimplify pattern <| function
           | Choice2Of2 errors ->
  -            List.rev errors
  -            |> List.toArray
  +            List.revIntoArray errors
               |> Choice2Of2
           | Choice1Of2 processedPattern ->
               Choice1Of2 processedPattern
  
positive.code:                 return err
              | Choice1Of2 r ->
                  return
                      Regex.Negate r
                      |> Choice1Of2
  
          (* Macro patterns *)
  
negative.code:             return
                  charSet
                  |> CharSet.difference universe
                  |> Regex.ofCharSet
  
          | Regex.Any
          | Regex.Epsilon
  