events/src/Events/Spec.hs


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{-# LANGUAGE GADTs #-}

module Events.Spec
       ( interpret
       , Spec, Cmnd(..), Expr(..)
       ) where

import Events.Types

import Control.Monad ((<=<))
import Control.Monad.IO.Class
import Control.Monad.State.Lazy

import Data.Monoid
import Data.Foldable
import Control.Lens

import Debug.Trace

type Spec = [Expr Cmnd] -- most significant last

data Cmnd = COverride Object
          | COccurs Bool
          | CNop
          deriving (Show)

data Expr a where
  ELit :: a -> Expr a

interpret :: MonadIO m => Spec -> Eval m ()
interpret = mapM_ $ interpretCmnd <=< interpretExpr

interpretExpr :: MonadIO m => Expr Cmnd -> m Cmnd
interpretExpr (ELit a) = return a

interpretCmnd :: MonadIO m => Cmnd -> Eval m ()
interpretCmnd (COverride obj) = objPayload ?= obj
interpretCmnd (COccurs b)     = objOccurs .= b
interpretCmnd _               = return ()