Automatic Enum representation

[f-f]

We thought that writing enum representations by hand was a lot of characters (our domain has quite a lot of sum types in some places), so we automated it.

Example from our codebase:

data SubscriptionState
  = Upcoming
  | Active
  | Canceled
  deriving (Show, Eq, Generic, Data, Enum, Bounded)

Before defining enumUnjsonDef we had to write this:

instance Unjson SubscriptionState where
  unjsonDef = enumOf "SubscriptionState"
    [ ("Upcoming", Upcoming)
    , ("Active"  , Active)
    , ("Canceled", Canceled)
    ]

After:

instance Unjson SubscriptionState where
  unjsonDef = enumUnjsonDef

Downsides of this: pulls in the TypeApplication extension, which was introduced in GHC 8.0. But if this is a problem I guess we could just add some other ifs on the GHC version to pull this in when possible.

[23Skidoo]

LGTM.

[23Skidoo]

Looks like the Travis build is failing due to TypeApplications not being supported on GHC <= 7.10.3.

[23Skidoo]

/cc @gracjan @mariuszrak

[gracjan]

I don't have an opionin really. You can drop support of GHC < 7.10.3 if it goes about me.

[mariuszrak]

LGTM

[23Skidoo]

Pushed some patches for older GHCs compat, dropped support for GHC 7.6. 7.8+/7.10 will still be supported for a while.

[23Skidoo]

Merged, thanks!

[f-f]

Thank you! Sorry for the hassle, I'll be more backwards-compatible next time.

I guess we can go forward with the new release :)

[jonathanjouty]

Personally, I don't think it is unfair to only support GHC >= 8 for new releases.

[23Skidoo]

Good rule of thumb is "support all GHC versions released in the last 3 years", which includes 7.10.3 at the moment.

[23Skidoo]

@f-f Released version 0.15.0.0 on Hackage.