Data.Vinyl.Generics.Transform

Generic functions to convert plain Haskell records to their vinyl representation and back.

Documentation

toVinyl :: (IsRecord a rs, NatTrans rs) => a -> Rec ElField rs

Given a plain record, returns the vinyl equivalent with the field names as type-level strings, tupled with the field type.

Example:

   import qualified Generics.SOP   as S
   import qualified GHC.Generics   as G

   data MyPlainRecord = MPR {
       age      :: Int,
       iscool   :: Bool,
       yearbook :: Text
     } deriving (Show, G.Generic)

   instance S.Generic MyPlainRecord
   instance S.HasDatatypeInfo MyPlainRecord
   -- Note: requires all 3 instances: G.Generic, S.Generic and S.HasDatatypeInfo

   -- this now works! Type signature is optional here.
   convertToVinyl :: MyPlainRecord
                  -> Rec ElField '[("age" ::: Int), ("iscool" ::: Bool), ("yearbook" ::: Text)]
   convertToVinyl  = toVinyl

fromVinyl :: (Generic a, Code a ~ ts, ts ~ '[ys], Cata rs ys) => Rec ElField rs -> a

Given a vinyl record, returns the plain record equivalent. Requires the equivalent plain record data declaration to be available in current scope.

Additionally, it requires explicit type annotation (either using a type signature or using TypeApplications).

Example:

   import qualified Generics.SOP   as S
   import qualified GHC.Generics   as G

   r1 :: Rec ElField '[("age" ::: Int), ("iscool" ::: Bool), ("yearbook" ::: Text)]
   r1 = xrec (23, True, "!123!")

   data MyPlainRecord = MPR {
       age      :: Int,
       iscool   :: Bool,
       yearbook :: Text
     } deriving (Show, G.Generic)

   instance S.Generic MyPlainRecord
   -- Note: Here we need only G.Generic and S.Generic

   -- Using explicit type signature
   r2 :: MyPlainRecord
   r2 = fromVinyl r1

   -- or using TypeApplications
   r2' = fromVinyl @MyPlainRecord r1