Re: GADTs in the wild

15 Aug 2012


      Well, "Either" was an adhoc choice and should be application specific.
Another h98 solution would be to keep the common part in a single 
constructor:

   data UserOrAppData = AppData | UserData UserId UTCTime
   data AccessToken = AccessToken UserOrAppData AccessTokenData

or: data AccessToken a = AccessToken a AccessTokenData

C.

Am 14.08.2012 18:32, schrieb Felipe Almeida Lessa:
...
2012/8/14 Christian Maeder :
...
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, =)