{-# LANGUAGE LambdaCase #-}
module Auxiliary (module Auxiliary) where
import           Control.Monad.Error.Class (liftEither)
import           Control.Monad.Except      (MonadError)
import           Data.Either.Combinators   (maybeToRight)

snoc :: a -> [a] -> [a]
snoc x xs = xs ++ [x]

maybeToRightM :: MonadError l m => l -> Maybe r -> m r
maybeToRightM err = liftEither . maybeToRight err

mapAccumM :: Monad m => (s -> a -> m (s, b)) -> s -> [a] -> m (s, [b])
mapAccumM f = go
  where
    go acc = \case
      [] -> pure (acc, [])
      x:xs -> do
        (acc', x') <- f acc x
        (acc'', xs') <- go acc' xs
        pure (acc'', x':xs')