Is there a package that does roughly the following:
Given a record:
data R = R { a :: TypeA,
b :: TypeB,
c :: TypeC }
derives a lifted record:
data R_L f = R_L { a_L :: f TypeA,
b_L :: f TypeB,
c_L :: f TypeC }
and offers a couple of instances and functions similar to:
instance (Monoid (f TypeA), Monoid (f TypeB), Monoid (f TypeC))
=> (Monoid (R_L f)) where
mempty = R_L mempty mempty mempty
mplus a b = ...fieldwise mplus...
sequenceR :: (Monad m) => R_L m -> m R
sequenceR = ... run fields, sum results ...
sequenceRA :: (Applicative m) => R_L m -> m R
sequenceRA x = R <$> a_L x <*> b_L x <*> c_L x
and probably others. Is there a package that provides this functionality and when not, which of the mechanisms (TH? Generics?) is best to use to implement it?
In the true open source spirit I wrote my own library: