yaml.hs

import Data.Text (Text)
import qualified Data.Yaml as Y
import Data.Yaml (FromJSON(..), (.:))
import Data.ByteString (ByteString)
import Text.RawString.QQ
import Control.Applicative

actionsYml :: ByteString
actionsYml = [r|
action:
  - description: some description
  - project: inbox
  - contexts: [ online, computer ]
|]

data Action =
    Action {
        description :: Text
      , project :: Text
      , contexts :: [Text]
    } deriving (Eq, Show)

instance FromJSON Action where
    parseJSON (Y.Object v) =
        Action <$>
        v .: "description" <*>
        v .: "project" <*>
        v .: "contexts"
    parseJSON _ = fail "Expected Object for Action value"

data Actions =
  Actions {
    action :: [Action]
  } deriving (Eq, Show)

instance FromJSON Actions where
  parseJSON (Y.Object v) =
    Actions <$>
      v .: "action"
  parseJSON _ = fail "Expected Object for Actions value"

main :: IO ()
main =
  print $ (Y.decode actionsYml :: Maybe(Actions))