diff --git a/IsNull.cabal b/IsNull.cabal --- a/IsNull.cabal +++ b/IsNull.cabal @@ -1,5 +1,5 @@ name: IsNull -version: 0.3.0.0 +version: 0.4.0.0 synopsis: A typeclass to determine if a given value is null. description: A typeclass to determine if a given foldable type (or other) is empty ~ null ~ invalid. @@ -8,7 +8,8 @@ homepage: https://github.com/jcristovao/IsNull license: BSD3 license-file: LICENSE -author: João Cristóvão +author: João Cristóvão + , Ivan Miljenovic maintainer: jmacristovao@gmail.com category: Data build-type: Simple @@ -19,17 +20,18 @@ cabal-version: >=1.16 library - other-modules: Data.IsNull.Internal - exposed-modules: Data.IsNull - build-depends: base >= 4.5 && < 4.8 - , base-compat >= 0.5 && < 0.6 - , containers >= 0.5 && < 0.6 - , text >= 0.11.3 && < 1.3 - , bytestring >= 0.10.0 && < 1.0 - hs-source-dirs: src ghc-options: -Wall default-language: Haskell2010 + exposed-modules: Data.IsNull + build-depends: base >= 4.5 && < 4.8 + , containers >= 0.5 && < 0.6 + , text >= 0.11.3 && < 1.3 + , bytestring >= 0.10.0 && < 1.0 + if impl(ghc < 7.7) + build-depends: + base-compat >= 0.5 && < 0.6 + -- the test suite checks for most (modern) applicable types -- found on Cabal. Exceptions: utf8-string, ListLike, IxSet @@ -38,8 +40,8 @@ type: exitcode-stdio-1.0 main-is: main.hs hs-source-dirs: test,src + default-language: Haskell2010 build-depends: base >= 4.5 && < 4.8 - , base-compat >= 0.5 && < 0.6 , containers >= 0.5 && < 0.6 , text >= 0.11.3 && < 1.3 , unordered-containers >= 0.2.3 @@ -51,7 +53,11 @@ , quickcheck-instances >= 0.3.5 , HUnit >= 1.2.5.2 , hspec >= 1.7.2 - default-language: Haskell2010 + if impl(ghc < 7.7) + build-depends: + base-compat >= 0.5 && < 0.6 + + source-repository head type: git diff --git a/src/Data/IsNull.hs b/src/Data/IsNull.hs --- a/src/Data/IsNull.hs +++ b/src/Data/IsNull.hs @@ -1,12 +1,11 @@ {-# LANGUAGE CPP #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE FlexibleContexts #-} -{-# LANGUAGE UndecidableInstances #-} -{-# LANGUAGE IncoherentInstances #-} +{-# LANGUAGE OverlappingInstances #-} {-# OPTIONS_GHC -fno-warn-orphans #-} {- | -Module: IsNull +Module: Data.IsNull Description: A typeclass to determine if a given value is null. Copyright: João Cristóvão, 2014 License: BSD3 @@ -35,8 +34,8 @@ is provided for the @'Monoid'@ class. It's up to you to use @(==) mempty@ instead. -The main use case for this package are boolean conditions, -namely the @if@ @then@ @else@ construct. +This class is suitable for use with @GeneralizedNewtypeDeriving@, +thanks to the precious help of Ivan Miljenovic. Bugs, suggestions and comments are most welcomed! @@ -44,10 +43,109 @@ -} module Data.IsNull ( - IsNull(..) + IsNull(..) + , notNull + , isNullN + , notNullN + , isNullM + , isNullNM + , (<\>) ) where +#if !MIN_VERSION_base(4,7,0) +import qualified Data.Foldable.Compat as F +#else +import qualified Data.Foldable as F +#endif +import qualified Data.Text as T +import qualified Data.Text.Lazy as LT +import qualified Data.ByteString as BS +import qualified Data.ByteString.Lazy as LBS +import qualified Data.IntSet as IS -import Data.IsNull.Internal +-- $setup +-- The code examples in this module require GHC's `OverloadedStrings` +-- extension: +-- +-- >>> :set -XOverloadedStrings + +class IsNull a where + -- | isNull ~ isEmpty ~ isInvalid? + -- + -- >>> isNull (Left 5) + -- True + -- + -- >>> isNull ("abc" :: T.Text) + -- False + -- + -- >>> isNull [""] -- see isNullN + -- False + isNull:: a -> Bool + +-- | the logical negation of @'isNull'@ +notNull :: (IsNull a) => a -> Bool +notNull = not . isNull + +-- | Nested isNull +-- +-- >>> isNullN (Just "abc") +-- False +-- +-- >>> isNullN (Just "") +-- True +-- +-- >>> isNullN (Nothing :: Maybe String) +-- True +isNullN :: (IsNull a, F.Foldable f) => f a -> Bool +isNullN = F.all isNull + +-- | Nested isNotNull +notNullN :: (IsNull a, F.Foldable f) => f a -> Bool +notNullN = not . isNullN + +-- | Monadic isNull +-- +-- >>> isNullM [""] +-- [True] +isNullM :: (IsNull a, Functor m) => m a -> m Bool +isNullM = fmap isNull + +-- | Monadic Nested isNull +isNullNM :: (IsNull a, Functor m, F.Foldable f) => m (f a) -> m Bool +isNullNM = fmap isNullN + +-- | @'Alternative'@'s @'<|>'@ operator does not always operate as choice, +-- at least not in an intuitive way (for example with lists). +-- This one does: +-- +-- >>> [2,3] <\> [4,5] +-- [2,3] +-- +-- >>> [] <\> [4,5] +-- [4,5] +-- +-- >>> [] <\> [] +-- [] +(<\>) :: (IsNull a) => a -> a -> a +(<\>) a b = if isNull a then b else a +infixl 3 <\> + +instance IsNull T.Text where + isNull = T.null + +instance IsNull LT.Text where + isNull = LT.null + +instance IsNull BS.ByteString where + isNull = BS.null + +instance IsNull LBS.ByteString where + isNull = LBS.null + +instance IsNull IS.IntSet where + isNull = IS.null + +instance F.Foldable f => IsNull (f a) where + isNull = F.foldr (\_ _ -> False) True diff --git a/src/Data/IsNull/Internal.hs b/src/Data/IsNull/Internal.hs deleted file mode 100644 --- a/src/Data/IsNull/Internal.hs +++ /dev/null @@ -1,102 +0,0 @@ -{-# LANGUAGE FlexibleInstances #-} -{-# LANGUAGE FlexibleContexts #-} -{-# LANGUAGE OverloadedStrings #-} -{-# OPTIONS_GHC -fno-warn-orphans #-} - -module Data.IsNull.Internal where - -import qualified Data.Foldable.Compat as F -import qualified Data.Text as T -import qualified Data.Text.Lazy as LT -import qualified Data.ByteString as BS -import qualified Data.ByteString.Lazy as LBS -import qualified Data.IntSet as IS -import Control.Monad (liftM) - - -class IsNull a where - -- | isNull ~ isEmpty ~ isInvalid? - -- - -- >>> isNull (Left 5) - -- True - -- - -- >>> isNull ("abc" :: T.Text) - -- False - -- - -- >>> isNull [""] -- see isNullN - -- False - isNull:: a -> Bool - - -- | Typing causes arthritis. Alias for @'isNull'@. - isN :: a -> Bool - isN = isNull - - -- | the logical negation of @'isNull'@ - notNull :: a -> Bool - notNull = not . isNull - - -- | Nested isNull - -- - -- >>> isNullN (Just "abc") - -- False - -- - -- >>> isNullN (Just "") - -- True - -- - -- >>> isNullN (Nothing :: Maybe String) - -- True - isNullN :: F.Foldable f => f a -> Bool - isNullN = F.all isNull - - -- | Nested isNotNull - notNullN :: F.Foldable f => f a -> Bool - notNullN = not . isNullN - - -- | Monadic isNull - -- - -- >>> isNullM [""] - -- [True] - isNullM :: Monad m => m a -> m Bool - isNullM = liftM isNull - - -- | Monadic Nested isNull - isNullNM :: (Monad m, F.Foldable f) => m (f a) -> m Bool - isNullNM = liftM isNullN - - -- | @'Alternative'@'s @'<|>'@ operator does not always operate as choice, - -- at least not in an intuitive way (for example with lists). - -- This one does: - -- - -- >>> [2,3] <\> [4,5] - -- [2,3] - -- - -- >>> [] <\> [4,5] - -- [4,5] - -- - -- >>> [] <\> [] - -- [] - (<\>) :: a -> a -> a - (<\>) a b = if isNull a then b else a - infixl 3 <\> - -instance IsNull Bool where - isNull = not - -instance IsNull T.Text where - isNull = T.null - -instance IsNull LT.Text where - isNull = LT.null - -instance IsNull BS.ByteString where - isNull = BS.null - -instance IsNull LBS.ByteString where - isNull = LBS.null - -instance IsNull IS.IntSet where - isNull = IS.null - -instance F.Foldable f => IsNull (f a) where - isNull = F.foldr (\_ _ -> False) True -