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{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE FunctionalDependencies #-}
module Events.Types
( TimeRange(..), rangeStart, rangeDuration
, Event(..), payload, occursWithin
, EvalCtx(..), ctxVars, ctxEvents
, Eval, evaluate
, module Data.Aeson
, module Data.Time.Clock
, module Data.Default.Class
) where
import Control.Lens.TH
import Data.Aeson (Object)
import Data.Time.Clock
import Control.Monad.State.Lazy
import ListT (ListT)
import qualified ListT
import Data.Default.Class
import Data.Monoid
import Control.Monad.Fix
import Control.Lens
import Data.Maybe
data TimeRange = TimeRange
{ _rangeStart :: UTCTime
, _rangeDuration :: NominalDiffTime
}
makeLenses ''TimeRange
data Event = Event
{ _payload :: Object
, _occursWithin :: TimeRange -> Bool
}
makeLenses ''Event
data EvalCtx = EvalCtx
{ _ctxVars :: Object
, _ctxEvents :: [Event]
}
makeLenses ''EvalCtx
instance Default EvalCtx where
def = EvalCtx
{ _ctxVars = mempty
, _ctxEvents = mempty
}
type Eval m a = ListT (StateT EvalCtx m) a
evaluate :: MonadFix m => Eval m (Maybe Event) -> m [Event]
evaluate x = catMaybes <$> mfix x'
where
x' = evalStateT (ListT.toList x) . flip (set ctxEvents) def . catMaybes
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