feat: UnresultT

src/Data.Postgres.Unresult.purs

@@ -0,0 +1,32 @@
+module Data.Postgres.Unresult where
+
+import Prelude
+
+import Control.Monad.Error.Class (class MonadThrow, liftMaybe)
+import Control.Monad.Morph (hoist)
+import Control.Monad.State (StateT(..), runStateT, state)
+import Control.Monad.Trans.Class (lift)
+import Data.Array as Array
+import Data.Maybe (fromMaybe, maybe)
+import Data.Postgres (class Deserialize, class Rep, RepT, deserialize, smash)
+import Data.Postgres.Raw (Raw)
+import Data.Postgres.Result (fromRow)
+import Data.Tuple (fst)
+import Data.Tuple.Nested ((/\))
+import Effect.Aff (error)
+import Effect.Class (class MonadEffect, liftEffect)
+import Effect.Exception (Error)
+
+-- | Monad used to incrementally deserialize columns from a row
+type UnresultT m a = StateT {ix :: Int, row :: Array Raw} m a
+
+-- | Run an `UnresultT`
+unresult :: forall m a. Monad m => Array Raw -> UnresultT m a -> m a
+unresult row m = fst <$> runStateT m {ix: 0, row}
+
+-- | Take the next column from the row, unmarshalling into `a`
+take :: forall m a. MonadThrow Error m => Deserialize a => MonadEffect m => UnresultT m a
+take = do
+  raw <- state (\r -> Array.index r.row r.ix /\ r {ix = r.ix + 1})
+  raw' <- liftMaybe (error "Ran out of columns!") raw
+  liftEffect $ smash $ deserialize raw'

src/Data.Postgres.purs

@@ -41,7 +41,7 @@ derive newtype instance ReadForeign a => ReadForeign (JSON a)
 foreign import modifyPgTypes :: Effect Unit
 
 -- | The serialization & deserialization monad.
-type RepT a = ExceptT (NonEmptyList ForeignError) Effect a
+type RepT = ExceptT (NonEmptyList ForeignError) Effect
 
 -- | Flatten to an Effect, `show`ing errors
 smash :: forall a. RepT a -> Effect a