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|
{-# LANGUAGE TemplateHaskell #-}
module Events.Types
( TimeRange(..), rangeStart, rangeDuration
, Event(..), payload, occursWithin
, EvalCtx(..), ctxEvents
, ObjCtx(..), objVars, objOccurs, objPayload
, Eval, evaluate
, module Data.Aeson
, module Data.Time.Clock
, module Data.Default.Class
) where
import Control.Lens.TH (makeLenses)
import Data.Aeson (Object)
import Data.Time.Clock (UTCTime, NominalDiffTime)
import Control.Monad.State.Lazy (StateT, evalStateT, execStateT)
import Data.Default.Class (Default(def))
-- import Data.Monoid
import Control.Monad.Fix (MonadFix(mfix))
import Control.Lens ((^.), set)
import Data.Maybe (catMaybes)
-- import Debug.Trace
import Events.Types.NDT (NDT, foldNDT)
data TimeRange = TimeRange
{ _rangeStart :: UTCTime
, _rangeDuration :: NominalDiffTime
}
makeLenses ''TimeRange
data Event = Event
{ _payload :: Object
, _occursWithin :: TimeRange -> Bool
}
makeLenses ''Event
data EvalCtx = EvalCtx
{ _ctxEvents :: [Object]
} deriving (Show)
makeLenses ''EvalCtx
instance Default EvalCtx where
def = EvalCtx
{ _ctxEvents = mempty
}
data ObjCtx = ObjCtx
{ _objOccurs :: Bool
, _objPayload :: Maybe Object
, _objVars :: Object
}
makeLenses ''ObjCtx
instance Default ObjCtx where
def = ObjCtx
{ _objOccurs = True
, _objPayload = Nothing
, _objVars = mempty
}
objCtx :: ObjCtx -> Maybe Object
objCtx ctx
| ctx ^. objOccurs = ctx ^. objPayload
| otherwise = Nothing
-- type Eval m a = StateT ObjCtx (ListT (StateT EvalCtx m)) a
-- evaluate :: MonadFix m => Eval m () -> m [Object] {- TODO: Switch to `ListT m Object` – `m [Object]` will turn out to be to strict. There is no instance for `MonadFix (ListT m)` – writing one seems to be possible. -}
-- evaluate x = catMaybes <$> mfix x'
-- where
-- x' = evalStateT (ListT.toList (objCtx <$> execStateT x def)) . flip (set ctxEvents) def . catMaybes
type Eval m a = StateT ObjCtx (NDT (StateT EvalCtx m)) a
evaluate :: MonadFix m => (Maybe Object -> StateT EvalCtx m Bool) -> Eval m () -> m [Object] {- TODO: Switch to `ListT m Object` – `m [Object]` will turn out to be to strict. There is no instance for `MonadFix (ListT m)` – writing one seems to be possible. -}
evaluate predicate x = catMaybes <$> mfix x'
where
x' = evalStateT (foldNDT predicate (objCtx <$> execStateT x def)) . flip (set ctxEvents) def . catMaybes
|
