{ name = "my-project"
, dependencies = [ "prelude", "safe-coerce" ]
, packages = ./packages.dhall
, sources = [ "src/**/*.purs", "test/**/*.purs" ]
}

let upstream =
      https://github.com/purescript/package-sets/releases/download/psc-0.13.6-20200423/packages.dhall sha256:c180a06bb5444fd950f8cbdd6605c644fd246deb397e62572b8f4a6b9dbcaf22

let overrides =
    { prelude =
        upstream.prelude // { version = "c932361d008379958f14ca8cc2fe32e06cc2647d" }
    }

let additions =
    { safe-coerce =
        { dependencies = [ "unsafe-coerce" ]
        , repo =
            "https://github.com/purescript/purescript-safe-coerce.git"
        , version = "v0.0.2"
        }
    }

in  upstream // overrides // additions

module Main where

import Prelude

import Safe.Coerce (coerce)

data Rep a
  = Leaf a
  | Link Int (Rep a) (Rep a)

data Rank

foreign import data Z :: Rank
foreign import data S :: Rank -> Rank

newtype Ranked :: Rank -> Type -> Type
newtype Ranked n a = Ranked a

type Tree n a = Ranked n (Rep a)

linkRep :: forall a. Rep a -> Rep a -> Rep a
linkRep t1 t2 = Link (rankRep t1 + 1) t1 t2

rankRep :: forall a. Rep a -> Int
rankRep =
  case _ of
    Leaf _ -> 0
    Link n _ _ -> n

badLink :: forall a n. Tree n a -> Tree n a -> Tree (S n) a
badLink t1 t2 = coerce (linkRep (coerce t1) (coerce t2))

goodLink :: forall a n. Tree n a -> Tree n a -> Tree (S n) a
goodLink (Ranked t1) (Ranked t2) = coerce (linkRep t1 t2)