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Add maybeField #311

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Add maybeField #311

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8 changes: 7 additions & 1 deletion src/Hakyll/Web/Template/Context.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ module Hakyll.Web.Template.Context
, Context (..)
, field
, constField
, maybeField
, listField
, listFieldWith
, functionField
Expand All @@ -28,7 +29,7 @@ module Hakyll.Web.Template.Context

--------------------------------------------------------------------------------
import Control.Applicative (Alternative (..), (<$>))
import Control.Monad (msum)
import Control.Monad (msum, (<=<))
import Data.List (intercalate)
import qualified Data.Map as M
import Data.Monoid (Monoid (..))
Expand Down Expand Up @@ -102,6 +103,11 @@ field key value = field' key (fmap StringField . value)
constField :: String -> String -> Context a
constField key = field key . const . return

--------------------------------------------------------------------------------
-- | A 'field' which will only contain value for 'Just's. This
-- is mostly useful along with conditional template construct @$if(key)$@.
maybeField :: String -> (Item a -> Compiler (Maybe String)) -> Context a
maybeField key value = field key $ maybe empty return <=< value

--------------------------------------------------------------------------------
listField :: String -> Context a -> Compiler [Item a] -> Context b
Expand Down