Deref.purs

module Deref where

import Prelude hiding (map, apply, pure)

import Record as Record
import Prelude as Prelude
import Prim.Row as Row
import Data.Symbol (SProxy(..), class IsSymbol)

data Deref r1 (r2 :: # Type) (r3 :: # Type) a = Deref ({ | r1 } -> a)

deref ::
  forall r1 r2 r3 rx sym a.
  IsSymbol sym =>
  Row.Cons sym a rx r1 =>
  Row.Cons sym a r2 r3 =>
  SProxy sym ->
  Deref r1 r2 r3 a
deref = Deref <<< Record.get

pure :: forall r1 r2 r3 a. a -> Deref r1 r2 r3 a
pure = Deref <<< const

map :: forall r1 r2 r3 a b. (a -> b) -> Deref r1 r2 r3 a -> Deref r1 r2 r3 b
map f (Deref k) = Deref (Prelude.map f k)

apply :: forall r1 r2 r3 r4 a b. Deref r1 r2 r3 (a -> b) -> Deref r1 r3 r4 a -> Deref r1 r2 r4 b
apply (Deref a) (Deref b) = Deref (Prelude.apply a b)

test = ado
  a <- deref (SProxy :: _ "a")
  b <- deref (SProxy :: _ "b")
  in a + b

runDeref :: forall r a. Deref r () r a -> { | r } -> a
runDeref (Deref k) = k

result = runDeref test { a: 1, b: 2 }