module Parsley.Internal.Core.Lam (normaliseGen, Lam(..)) where

import Parsley.Internal.Common.Utils (Code)

data Lam a where
    Abs :: (Lam a -> Lam b) -> Lam (a -> b)
    App :: Lam (a -> b) -> Lam a -> Lam b
    Var :: Bool {- Simple -} -> Code a -> Lam a
    If  :: Lam Bool -> Lam a -> Lam a -> Lam a
    Let :: Lam a -> (Lam a -> Lam b) -> Lam b
    T   :: Lam Bool
    F   :: Lam Bool

normalise :: Lam a -> Lam a
normalise :: Lam a -> Lam a
normalise Lam a
x = Lam a -> Lam a
forall a. Lam a -> Lam a
reduce Lam a
x
  where
    reduce :: Lam a -> Lam a
    reduce :: Lam a -> Lam a
reduce Lam a
x
      | Lam a -> Bool
forall a. Lam a -> Bool
normal Lam a
x = Lam a
x
      | Bool
otherwise = Lam a -> Lam a
forall a. Lam a -> Lam a
reduce (Lam a -> Lam a
forall a. Lam a -> Lam a
reduceStep Lam a
x)

    reduceStep :: Lam a -> Lam a
    reduceStep :: Lam a -> Lam a
reduceStep (App (Abs Lam a -> Lam b
f) Lam a
x) = Lam a -> Lam b
f Lam a
Lam a
x
    reduceStep (App Lam (a -> a)
f Lam a
x)
      | Lam (a -> a) -> Bool
forall a. Lam a -> Bool
normal Lam (a -> a)
f = Lam (a -> a) -> Lam a -> Lam a
forall a b. Lam (a -> b) -> Lam a -> Lam b
App Lam (a -> a)
f (Lam a -> Lam a
forall a. Lam a -> Lam a
reduceStep Lam a
x)
      | Bool
otherwise = Lam (a -> a) -> Lam a -> Lam a
forall a b. Lam (a -> b) -> Lam a -> Lam b
App (Lam (a -> a) -> Lam (a -> a)
forall a. Lam a -> Lam a
reduceStep Lam (a -> a)
f) Lam a
x
    reduceStep (If Lam Bool
T Lam a
x Lam a
_) = Lam a
x
    reduceStep (If Lam Bool
F Lam a
_ Lam a
y) = Lam a
y
    reduceStep Lam a
x = Lam a
x

    normal :: Lam a -> Bool
    normal :: Lam a -> Bool
normal (App (Abs Lam a -> Lam b
_) Lam a
_) = Bool
False
    normal (App Lam (a -> a)
f Lam a
x) = Lam (a -> a) -> Bool
forall a. Lam a -> Bool
normal Lam (a -> a)
f Bool -> Bool -> Bool
&& Lam a -> Bool
forall a. Lam a -> Bool
normal Lam a
x
    normal (If Lam Bool
T Lam a
_ Lam a
_) = Bool
False
    normal (If Lam Bool
F Lam a
_ Lam a
_) = Bool
False
    normal Lam a
_ = Bool
True

generate :: Lam a -> Code a
generate :: Lam a -> Code a
generate (Abs Lam a -> Lam b
f)    = [||\x -> $$(normaliseGen (f (Var True [||x||])))||]
-- These have already been reduced, since we only expose `normaliseGen`
generate (App Lam (a -> a)
f Lam a
x)  = [||$$(generate f) $$(generate x)||]
generate (Var Bool
_ Code a
x)  = Code a
x
generate (If Lam Bool
c Lam a
t Lam a
e) = [||if $$(normaliseGen c) then $$(normaliseGen t) else $$(normaliseGen e)||]
generate (Let Lam a
b Lam a -> Lam a
i)  = [||let x = $$(normaliseGen b) in $$(normaliseGen (i (Var True [||x||])))||]
generate Lam a
T          = [||True||]
generate Lam a
F          = [||False||]

normaliseGen :: Lam a -> Code a
normaliseGen :: Lam a -> Code a
normaliseGen = Lam a -> Code a
forall a. Lam a -> Code a
generate (Lam a -> Code a) -> (Lam a -> Lam a) -> Lam a -> Code a
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Lam a -> Lam a
forall a. Lam a -> Lam a
normalise