3558-UpToDateDictsForHigherOrderFns.purs

module Main where

import Prelude (Unit)
import Effect (Effect)
import Effect.Console (log)
import Record.Unsafe (unsafeGet)
import Type.Data.Symbol (class IsSymbol, SProxy, reflectSymbol)
import Type.Row (class Cons) as Row

newtype LBox row a = LBox (∀ r. (∀ lbl _1. Row.Cons lbl a _1 row ⇒ IsSymbol lbl ⇒ SProxy lbl → r) → r)

unLBox ∷ ∀ row a r. (∀ lbl _1. Row.Cons lbl a _1 row ⇒ IsSymbol lbl ⇒ SProxy lbl → r) → LBox row a → r
unLBox g (LBox f) = f g

-- Example 1
lboxIdentity ∷ ∀ row a. LBox row a → LBox row a
lboxIdentity = unLBox \lbl → LBox \f → f lbl

-- Example 2
read ∷ ∀ row a. Record row → LBox row a → a
read rec = unLBox \lbl → get lbl rec

get
  :: forall r r' l a
   . IsSymbol l
  => Row.Cons l a r' r
  => SProxy l
  -> Record r
  -> a
get l r = unsafeGet (reflectSymbol l) r

main :: Effect Unit
main = log "Done"