{-# LANGUAGE PatternSynonyms #-}
module Syntax where

import Data.Function (on)
import Data.Text (Text)

import Presyntax.Presyntax (Plicity(..))
import qualified Data.Text as T
import Data.IORef (IORef)

data Term
  = Ref  Name
  | App  Plicity Term Term
  | Lam  Plicity Text Term
  | Pi   Plicity Text Term Term
  | Meta MV
  | Type

  | Sigma Text Term Term
  | Pair Term Term
  | Proj1 Term
  | Proj2 Term
  deriving (Eq, Show, Ord)

data MV =
  MV { mvName :: Text
     , mvCell :: {-# UNPACK #-} !(IORef (Maybe Value))
     }

instance Eq MV where
  (==) = (==) `on` mvName
instance Ord MV where
  (<=) = (<=) `on` mvName
instance Show MV where
  show = ('?':) . T.unpack . mvName

data Name
  = Bound Text
  deriving (Eq, Show, Ord)

type NFType = Value

data Value
  = VNe    Head            [Projection]
  | VLam   Plicity         Closure
  | VPi    Plicity Value   Closure
  | VSigma Value   Closure
  | VPair  Value   Value
  | VType
  deriving (Eq, Show, Ord)

pattern VVar :: Name -> Value
pattern VVar x = VNe (HVar x) []

quote :: Value -> Term
quote (VNe h sp) = foldl goSpine (goHead h) (reverse sp) where
  goHead (HVar v) = Ref v
  goHead (HMeta m) = Meta m

  goSpine t (PApp p v) = App p t (quote v)
  goSpine t PProj1 = Proj1 t
  goSpine t PProj2 = Proj2 t

quote (VLam p (Closure n k))   = Lam p n (quote (k (VVar (Bound n))))
quote (VPi p d (Closure n k))  = Pi p n (quote d) (quote (k (VVar (Bound n))))
quote (VSigma d (Closure n k)) = Sigma n (quote d) (quote (k (VVar (Bound n))))
quote (VPair a b) = Pair (quote a) (quote b)
quote VType = Type

data Closure
  = Closure
    { clArgName :: Text
    , clCont    :: Value -> Value
    }

instance Show Closure where
  show (Closure n c) = "Closure \\" ++ show n ++ " -> " ++ show (c (VVar (Bound n)))

instance Eq Closure where
  Closure _ k == Closure _ k' =
    k (VVar (Bound (T.pack "_"))) == k' (VVar (Bound (T.pack "_")))

instance Ord Closure where
  Closure _ k <= Closure _ k' =
    k (VVar (Bound (T.pack "_"))) <= k' (VVar (Bound (T.pack "_")))

data Head
  = HVar Name
  | HMeta MV
  deriving (Eq, Show, Ord)

data Projection
  = PApp Plicity Value
  | PProj1
  | PProj2
  deriving (Eq, Show, Ord)