GADTs in the wild

[Felipe Almeida Lessa]

2012/8/14 Christian Maeder <Christian.Maeder at dfki.de>:
> Why not use plain h98?
>
>   data UserAccessToken = UserAccessToken UserId AccessTokenData UTCTime
>   data AppAccessToken = AppAccessToken AccessTokenData
>
>   type AccessToken = Either UserAccessToken AppAccessToken

Convenience.  It's better to write

  case token of
    UserAccessToken ... -> ...
    AppAccessToken ... -> ...

than

  case token of
    Left (UserAccessToken ...) -> ...
    Right (UserAccessToken ...) -> ...

Also, it's easier to write

  isValid token

than

  isValid (Right token)  -- or is it Left?

Cheers, =)

-- 
Felipe.