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Add Context instances for Contravariant, Divisible, Decidable #577

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Add Context instances for Contravariant, Divisible, Decidable #577

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2 changes: 2 additions & 0 deletions hakyll.cabal
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Original file line number Diff line number Diff line change
Expand Up @@ -159,6 +159,7 @@ Library
blaze-markup >= 0.5.1 && < 0.9,
bytestring >= 0.9 && < 0.11,
containers >= 0.3 && < 0.6,
contravariant >= 1.0 && < 1.5,
cryptohash >= 0.7 && < 0.12,
data-default >= 0.4 && < 0.8,
deepseq >= 1.3 && < 1.5,
Expand Down Expand Up @@ -254,6 +255,7 @@ Test-suite hakyll-tests
blaze-markup >= 0.5.1 && < 0.9,
bytestring >= 0.9 && < 0.11,
containers >= 0.3 && < 0.6,
contravariant >= 1.0 && < 1.5,
cryptohash >= 0.7 && < 0.12,
data-default >= 0.4 && < 0.8,
deepseq >= 1.3 && < 1.5,
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35 changes: 26 additions & 9 deletions lib/Hakyll/Web/Template/Context.hs
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Expand Up @@ -32,22 +32,25 @@ module Hakyll.Web.Template.Context


--------------------------------------------------------------------------------
import Control.Applicative (Alternative (..))
import Control.Monad (msum)
import Data.List (intercalate)
import Data.Time.Clock (UTCTime (..))
import Data.Time.Format (formatTime)
import qualified Data.Time.Format as TF
import Data.Time.Locale.Compat (TimeLocale, defaultTimeLocale)
import Control.Applicative (Alternative (..))
import Control.Monad (msum)
import Data.Functor.Contravariant (Contravariant (..))
import Data.Functor.Contravariant.Divisible (Decidable (..), Divisible (..))
import Data.List (intercalate)
import Data.Time.Clock (UTCTime (..))
import Data.Time.Format (formatTime)
import qualified Data.Time.Format as TF
import Data.Time.Locale.Compat (TimeLocale, defaultTimeLocale)
import Data.Void (absurd)
import Hakyll.Core.Compiler
import Hakyll.Core.Compiler.Internal
import Hakyll.Core.Identifier
import Hakyll.Core.Item
import Hakyll.Core.Metadata
import Hakyll.Core.Provider
import Hakyll.Core.Util.String (needlePrefix, splitAll)
import Hakyll.Core.Util.String (needlePrefix, splitAll)
import Hakyll.Web.Html
import System.FilePath (splitDirectories, takeBaseName)
import System.FilePath (splitDirectories, takeBaseName)


--------------------------------------------------------------------------------
Expand Down Expand Up @@ -83,6 +86,20 @@ instance Monoid (Context a) where
mappend (Context f) (Context g) = Context $ \k a i -> f k a i <|> g k a i


--------------------------------------------------------------------------------
instance Contravariant Context where
contramap f (Context g) = Context $ \k a i -> g k a (f <$> i)

instance Divisible Context where
conquer = mempty
divide f c1 c2 = contramap (fst . f) c1 `mappend` contramap (snd . f) c2

instance Decidable Context where
lose refute = Context $ \_k _a i -> absurd . refute . itemBody $ i
choose chooser (Context f) (Context g) = Context $ \k a i -> case chooser (itemBody i) of
Left l -> f k a (itemSetBody l i)
Right r -> g k a (itemSetBody r i)

--------------------------------------------------------------------------------
field' :: String -> (Item a -> Compiler ContextField) -> Context a
field' key value = Context $ \k _ i -> if k == key then value i else empty
Expand Down