Stock: Stock-style deriving via coercion, with no Generic

[Iceland_jack]

A package for extensible compile-time deriving: stock: Stock-style deriving via coercion, with no Generic

More information: Reddit - Please wait for verification

[BurningWitness]

@Iceland_jack

data Inventory = Inventory
  { hp       :: Int              -- (+)
  , coins    :: Int              -- (+)
  , poisoned :: Bool             -- (||)
  , items    :: Map Item Int     -- unionWith (+)
  , weapons  :: Map Weapon Int   -- unionWith (+)
  }
  deriving (Eq, Ord, Show, Read) via 
    Stock Inventory
  deriving (Semigroup, Monoid) via
    Overriding Inventory
     '[ hp       via Sum
      , coins    via Sum
      , poisoned via Any
      , items    via MultiSet Item
      , weapons  via MultiSet Weapon
      ]

Wow, this is as verbose as writing a function manually, except it needs no underlying library implementing [and documenting] all of the helper functions, has no convenience of a function declaration, and forces a dependency on a GHC plugin.

In the case of aeson, where I’ve long complained there are no proper functions for writing parsers manually, this is akin to implementing them on top of Generics.

[sjoerdvisscher]

You typically wouldn’t override all the fields. I’d use a library like this if I have a lot fields (10 or more perhaps) and only a few of them need overriding. And even if it would be equally long, I’d much prefer a declarative, correct by construction derived instance than code, no matter how clear, that I’d need to read to check for subtle mistakes, or would have to write boring tests for.

[wiz]

Stoked to derive some profunctors!

[taylorfausak]

Whoa, this is awesome!