get environment variables in F#

NicerEnv.fs

let dict_map (dict : System.Collections.IDictionary) =
  let values = ref (Map<'a,'b> [])
  for obj in dict do
    let de = obj :?> System.Collections.DictionaryEntry
    values := Map.add (de.Key :?> 'a) (de.Value :?> 'b) !values
  !values

System.Environment.GetEnvironmentVariables() |> dict_map<string,string>