quiet

Generic deriving of Read/Show with no record labels.

Monthly Downloads: 127

Programming language: Haskell

License: BSD 3-clause "New" or "Revised" License

Tags: Generics    

README

quiet

Generic deriving of Read / Show with no record labels.

Often one wants to create a newtype which has a convenient field accessor like unUserId below, but that unfortunately makes the Show instance which is derived overly verbose.

For example:

newtype UserId = UserId { unUserId :: String }
  deriving (Read, Show)

ghci> show (UserId "simon")
UserId {unUserId = "simon"}
ghci> read "UserId {unUserId = \"simon\"}" :: UserId
UserId {unUserId = "simon"}

With DerivingVia Quiet you can have a Show instance which doesn't print the field labels. It will render as if the unUserId accessor wasn't present at all.

newtype UserId = UserId { unUserId :: String }
  deriving (Generic)
  deriving (Read, Show) via (Quiet UserId)

ghci> show (UserId "simon")
UserId "simon"
ghci> read "UserId \"simon\"" :: UserId
UserId "simon"

If you want to derive Read / Show without using DerivingVia then you can use qreadPrec and qshowsPrec directly.

instance Read UserId where readPrec = qreadPrec
instance Show UserId where showsPrec = qshowsPrec