gistfile1.txt

selectUnValued :: (MonadIO m, UnValueAll a a', SqlSelect (SqlExpr a) a) => SqlQuery (SqlExpr a) -> SqlPersistT m [a']
selectUnValued = fmap (map unValueAll) . select

unValueAll :: (UnValueAll a a') => a -> a'
unValueAll = unV

class UnValueAll a b where
  unV :: a -> b

instance UnValueAll (Value a) a where
  unV (Value a) = a

instance UnValueAll (Entity a) (Entity a) where
  unV = id

instance UnValueAll (Maybe (Entity a)) (Maybe (Entity a)) where
  unV = id

instance (UnValueAll a a', UnValueAll b b') => UnValueAll (a, b) (a', b') where unV (a, b) = (unV a, unV b)

instance (UnValueAll a a', UnValueAll b b', UnValueAll c c') => UnValueAll (a, b, c) (a', b', c') where unV (a, b, c) = (unV a, unV b, unV c)

instance (UnValueAll a a', UnValueAll b b', UnValueAll c c', UnValueAll d d') => UnValueAll (a, b, c, d) (a', b', c', d') where unV (a, b, c, d) = (unV a, unV b, unV c, unV d)

instance (UnValueAll a a', UnValueAll b b', UnValueAll c c', UnValueAll d d', UnValueAll e e') => UnValueAll (a, b, c, d, e) (a', b', c', d', e') where unV (a, b, c, d, e) = (unV a, unV b, unV c, unV d, unV e)

instance (UnValueAll a a', UnValueAll b b', UnValueAll c c', UnValueAll d d', UnValueAll e e', UnValueAll f f') => UnValueAll (a, b, c, d, e, f) (a', b', c', d', e', f') where unV (a, b, c, d, e, f) = (unV a, unV b, unV c, unV d, unV e, unV f)

instance (UnValueAll a a', UnValueAll b b', UnValueAll c c', UnValueAll d d', UnValueAll e e', UnValueAll f f', UnValueAll g g') => UnValueAll (a, b, c, d, e, f, g) (a', b', c', d', e', f', g') where unV (a, b, c, d, e, f, g) = (unV a, unV b, unV c, unV d, unV e, unV f, unV g)