failure (empty) → 0.0.0

raw patch · 3 files changed

+128/−0 lines, 3 filesdep +basesetup-changed

Dependencies added: base

Files

• Control/Failure.hs +97/−0
• Setup.lhs +7/−0
• failure.cabal +24/−0

@@ -0,0 +1,97 @@+{-# LANGUAGE Rank2Types #-}+{-# LANGUAGE TypeFamilies #-}+{-# LANGUAGE MultiParamTypeClasses #-}+{-# LANGUAGE FlexibleInstances #-}+{-# LANGUAGE UndecidableInstances #-}+{-# LANGUAGE DeriveDataTypeable #-}+{-# LANGUAGE FlexibleContexts #-}+-- | Type classes for returning failures.+module Control.Failure+    ( -- * Type classes+      Failure (..)+    , FunctorFailure+    , ApplicativeFailure+    , MonadFailure+      -- * Wrapping failures+    , WrapFailure (..)+      -- * Convenience 'String' failure+    , StringException (..)+    , failureString+      -- * Convert 'Failure's into concrete types+    , Try (..)+    , NothingException (..)+    , NullException (..)+    ) where++import Prelude hiding (catch)+import Control.Exception (throw, catch, Exception, SomeException (..))+import Data.Typeable (Typeable)+import Control.Applicative (Applicative, pure)++class Failure e f where+    failure :: e -> f v+class (Functor f, Failure e f) => FunctorFailure e f+class (Applicative f, Failure e f) => ApplicativeFailure e f+class (Monad f, Applicative f, Failure e f) => MonadFailure e f++-- These introduce the need to use undecidables.+-- However, since they are merely type class synonyms, this is acceptable.+instance (Functor f, Failure e f) => FunctorFailure e f+instance (Applicative f, Failure e f) => ApplicativeFailure e f+instance (Monad f, Applicative f, Failure e f) => MonadFailure e f++class Failure e f => WrapFailure e f where+    -- | Wrap the failure value, if any, with the given function. This is+    -- useful in particular when you want all the exceptions returned from a+    -- certain library to be of a certain type, even if they were generated by+    -- a different library.+    wrapFailure :: (forall eIn. Exception eIn => eIn -> e) -> f a -> f a+instance Exception e => WrapFailure e IO where+    wrapFailure f m =+        m `catch` \e@SomeException{} -> throw (f e)++class Try f where+  type Error f+  -- Turn a concrete failure into an abstract failure+  try :: ApplicativeFailure (Error f) f' => f a -> f' a++-- | Call 'failure' with a 'String'.+failureString :: Failure StringException m => String -> m a+failureString = failure . StringException++newtype StringException = StringException String+    deriving Typeable+instance Show StringException where+    show (StringException s) = "StringException: " ++ s+instance Exception StringException++-- --------------+-- base instances+-- --------------++instance Failure e Maybe where failure _ = Nothing+instance Failure e []    where failure _ = []++instance Exception e => Failure e IO where+  failure = Control.Exception.throw++instance Failure e (Either e) where failure = Left++data NothingException = NothingException+  deriving (Show, Typeable)+instance Try Maybe where+  type Error Maybe = NothingException+  try Nothing      = failure NothingException+  try (Just x)     = pure x++instance Try (Either e) where+  type Error (Either e) = e+  try (Left  e)         = failure e+  try (Right x)         = pure x++data NullException = NullException+  deriving (Show, Typeable)+instance Try [] where+  type Error [] = NullException+  try []        = failure NullException+  try (x:_)     = pure x

@@ -0,0 +1,7 @@+#!/usr/bin/env runhaskell++> module Main where+> import Distribution.Simple++> main :: IO ()+> main = defaultMain

@@ -0,0 +1,24 @@+name: failure+version: 0.0.0+Cabal-Version:  >= 1.6+build-type: Simple+license: PublicDomain+author: Pepe Iborra, Michael Snoyman, Nicolas Pouillard+maintainer: pepeiborra@gmail.com+homepage: http://github.com/snoyberg/failure+description: A simple type class for success/failure computations.+synopsis: A simple type class for success/failure computations.+category: Control, Monads, Failure+stability: stable++Library+  buildable: True+  build-depends: base >= 4 && < 5+  ghc-options: -Wall++  exposed-modules:+     Control.Failure++source-repository head+  type:     git+  location: git://github.com/snoyberg/failure.git