anchor.diff:              let before = value.Substring(0, index)
               let after = value.Substring(index + search.Length)
               let replace = replace |> TC.ToString
  -            let replace = evaluateReplacement search before after replace null
  +            let replace = evaluateReplacement search (fun () -> before) (fun () -> after) replace null
               before + replace + after
   
           else
  
positive.code: 
        else
          replacement
  
      ///
      let private replace (_:FO) (this:CO) (search:BV) (replace:BV) =
  
negative.code:             | "$0" -> "$0"
              | "$00" -> "$00"
              | "$&" -> matched
              | "$`" -> before()
              | "$'" -> after()
              | _ ->
                let subPatternIndex = t.Substring 1 |> int
                if groups <> null && subPatternIndex < groups.Count
  