Quiet

Generic deriving of Read / Show with no record labels.

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

For example:

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

Renders as:

>>> show (UserId "simon")
UserId {unUserId = "simon"}

With qshowsPrec 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)

instance Show UserId where showsPrec = qshowsPrec

>>> show (UserId "simon")
UserId "simon"

A compatible Read instance can also be derived using qreadPrec if necessary.

instance Read UserId where showsPrec = qreadPrec

Documentation

qshowsPrec :: (Generic a, QShow (Rep a)) => Int -> a -> ShowS

This implements a quiet version of showsPrec which omits labels for record fields when rendering constructors.

qreadPrec :: (Generic a, QRead (Rep a)) => ReadPrec a

This implements a quiet version of readPrec which expects labels for record fields to be omitted when parsing constructors.