let rec build currentIndex (currentMatch: Match) =
    if currentMatch.Success then
        let variableToReplace = currentMatch.Groups.[0]
        let length = variableToReplace.Index - currentIndex
        let subUrl = url.Substring(currentIndex, length)
        builder.Append(subUrl) |> ignore
        let replaceWith =
            match currentMatch.Groups.[1].Value with
            | "INT" -> "INTEGER" // replace with int generator
            | _ -> "OBJECT" // optionally other data types
        builder.Append(replaceWith) |> ignore
        build (subUrl.Length + variableToReplace.Length) (currentMatch.NextMatch())
    else
        builder.ToString()
build 0 (variableRegex.Match(url))