MonadSelda + ExceptT

ExceptSelda.hs

{-# LANGUAGE DeriveGeneric, OverloadedStrings, OverloadedLabels #-}
import Database.Selda
import Database.Selda.Backend (MonadSelda (..))
import Database.Selda.SQLite
import Control.Monad.Except

instance (MonadMask m, MonadSelda m) => MonadSelda (ExceptT e m) where
  seldaConnection = ExceptT (Right <$> seldaConnection)

type ExceptSeldaT e m = ExceptT e (SeldaT m)

run :: (MonadIO m, MonadMask m)
    => FilePath
    -> ExceptSeldaT e m a
    -> m (Either e a)
run file = withSQLite file . runExceptT

data Foo = Foo
  { id :: ID Foo
  , foo :: Int
  } deriving (Show, Generic)
instance SqlRow Foo

foos :: Table Foo
foos = table "foos" [#id :- autoPrimary]

getFoos :: ExceptSeldaT Text IO [Foo]
getFoos = do
  fs <- lift $ query $ select foos
  when (null fs) $ throwError "There were no foos!"
  return fs