{-# LANGUAGE PatternSynonyms, ViewPatterns #-}
module Parsley.Internal.Backend.Machine.Defunc (module Parsley.Internal.Backend.Machine.Defunc) where

import Parsley.Internal.Backend.Machine.InputOps (PositionOps(same))
import Parsley.Internal.Common.Utils             (Code)
import Parsley.Internal.Core.Lam                 (Lam, normaliseGen, normalise)

import qualified Parsley.Internal.Core.Defunc as Core (Defunc, lamTerm)
import qualified Parsley.Internal.Core.Lam    as Lam  (Lam(..))

data Defunc a where
  LAM     :: Lam a -> Defunc a
  BOTTOM  :: Defunc a
  INPUT   :: Code o -> (Code Int, Code Int) -> Defunc o
  SAME    :: PositionOps o => Defunc (o -> o -> Bool)

user :: Core.Defunc a -> Defunc a
user = LAM . Core.lamTerm

ap :: Defunc (a -> b) -> Defunc a -> Defunc b
ap f x = LAM (Lam.App (unliftDefunc f) (unliftDefunc x))

ap2 :: Defunc (a -> b -> c) -> Defunc a -> Defunc b -> Defunc c
ap2 SAME (INPUT o1 _) (INPUT o2 _) = LAM (Lam.Var False [|| $$same $$o1 $$o2 ||])
ap2 f x y = ap (ap f x) y

_if :: Defunc Bool -> Code a -> Code a -> Code a
_if c t e = normaliseGen (Lam.If (unliftDefunc c) (Lam.Var False t) (Lam.Var False e))

unliftDefunc :: Defunc a -> Lam a
unliftDefunc (LAM x) = x
unliftDefunc x       = Lam.Var False (genDefunc x)

genDefunc :: Defunc a -> Code a
genDefunc (LAM x) = normaliseGen x
genDefunc BOTTOM  = [||undefined||]
genDefunc INPUT{} = error "Cannot materialise an input in the regular way"
genDefunc SAME    = same

pattern NormLam :: Lam a -> Defunc a
pattern NormLam t <- LAM (normalise -> t)

pattern FREEVAR :: Code a -> Defunc a
pattern FREEVAR v <- NormLam (Lam.Var True v)
  where
    FREEVAR v = LAM (Lam.Var True v)

instance Show (Defunc a) where
  show (LAM x) = show x
  show SAME = "same"
  show INPUT{} = "input"
  show BOTTOM = "[[irrelevant]]"