fromValue family of functions about esqueleto HOT 4 OPEN

+1

from esqueleto.

How about

class FromValue a where
    type UnValue a
    fromValue :: a -> UnValue a

instance FromValue (Value a) where
    type UnValue (Value a) = a
    fromValue (Value a) = a

instance (FromValue a, FromValue b) => FromValue (a, b) where
    type UnValue (a, b) = (UnValue a, UnValue b)
    fromValue (a, b) = (fromValue a, fromValue b)

etc.

from esqueleto.

Why not make Value an instance of Applicative and Comonad, which both make sense, I would also include Foldable, Traversable and Monad which would be an easy task.

also I think it would make sense to put in cpp stanzas to make Value/ValueList newtypes - since
the definition of Value on hackage says

-- Note: because of GHC bug #6124 we use @data@ instead of @newtype@.
-- <https://ghc.haskell.org/trac/ghc/ticket/6124>

should be obsolete in GHC later than 8.0.1.

from esqueleto.

@meteficha I'd be willing to provide a PR for that

from esqueleto.