v 0.20.1

Web/Scotty/Internal/Types.hs

@@ -1,7 +1,6 @@
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE DeriveDataTypeable #-}
 {-# LANGUAGE DerivingStrategies #-}
-{-# language DerivingVia #-}
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
@@ -207,6 +206,10 @@ defaultScottyResponse = SR status200 [] (ContentBuilder mempty)
 
 newtype ActionT m a = ActionT { runAM :: ReaderT ActionEnv m a }
   deriving newtype (Functor, Applicative, Monad, MonadIO, MonadReader ActionEnv, MonadTrans, MonadThrow, MonadCatch, MonadBase b, MonadBaseControl b, MonadTransControl, MonadUnliftIO)
+-- | Modeled after the behaviour in scotty < 0.20, 'fail' throws a 'StatusError' with code 500 ("Server Error"), which can be caught with 'E.catch' or 'rescue'.
+instance (MonadIO m) => MonadFail (ActionT m) where
+  fail = E.throw . StatusError status500 . pack
+-- | 'empty' throws 'ActionError' 'AENext', whereas '(<|>)' catches any 'ActionError's or 'StatusError's in the first action and proceeds to the second one.
 instance (MonadUnliftIO m) => Alternative (ActionT m) where
   empty = E.throw AENext
   a <|> b = do

changelog.md

@@ -1,6 +1,9 @@
 ## next [????.??.??]
 
+## 0.20.1 [2023.10.03]
+
 * remove dependencies on 'base-compat' and 'base-compat-batteries' (#318)
+* re-add MonadFail (ActionT m) instance (#325)
 
 ## 0.20 [2023.10.02]
 * Drop support for GHC < 8.10 and modernise the CI pipeline (#300).
@@ -14,8 +17,9 @@
 Breaking:
 
 * (#310) Introduce `unliftio` as a dependency, and base exception handling on `catch`.
-** Clarify the exception handling mechanism of ActionT, ScottyT. `rescue` changes signature to use proper `Exception` types rather than strings.
-** All ActionT methods (`text`, `html` etc.) have now a MonadIO constraint on the base monad rather than Monad because the response is constructed in a TVar inside ActionEnv. `rescue` has a MonadUnliftIO constraint. The Alternative instance of ActionT also is based on MonadUnliftIO because `<|>` is implemented in terms of `catch`. `ScottyT` and `ActionT` do not have an exception type parameter anymore.
+* (#310) Clarify the exception handling mechanism of ActionT, ScottyT. `rescue` changes signature to use proper `Exception` types rather than strings. Remove `ScottyError` typeclass.
+* (#310) All ActionT methods (`text`, `html` etc.) have now a MonadIO constraint on the base monad rather than Monad because the response is constructed in a TVar inside ActionEnv. `rescue` has a MonadUnliftIO constraint. The Alternative instance of ActionT also is based on MonadUnliftIO because `<|>` is implemented in terms of `catch`. `ScottyT` and `ActionT` do not have an exception type parameter anymore.
+* (#310) MonadFail (ActionT m) instance is missing by mistake.
 
 ## 0.12.1 [2022.11.17]
 * Fix CPP bug that prevented tests from building on Windows.

scotty.cabal

@@ -1,5 +1,5 @@
 Name:                scotty
-Version:             0.20
+Version:             0.20.1
 Synopsis:            Haskell web framework inspired by Ruby's Sinatra, using WAI and Warp
 Homepage:            https://github.com/scotty-web/scotty
 Bug-reports:         https://github.com/scotty-web/scotty/issues