Space leak / error in the interaction of Control.Lens.Plated and Bound

Question

Using the latest version Boundand Control.Lens.Plated, the next call transformcauses the program to end endlessly and happily in my RAM. The termination of the program leads to the fact that the correct result is printed, although I do not know why.

I traced the problem to the data type Scope. Deleting this file causes the program to behave as expected.

Profiling with ./program +RTS -p -hshows Data.Data.Lens.insertHitMap.populatehow the problem is. Some profiling included.

Is this expected behavior with an official workaround or could it be a mistake?

I am using GHC version 8.0.2, all packages except bound-2are part of the stack lts-8.17. The program is compiled as ghc test.hs. Enabling or disabling optimizations does not affect the problem.

As I suspect this is a mistake, I opened the issue for this in the repository ekmett Bound(for cross-referencing).

---

-- file: test.hs
{-# LANGUAGE DeriveFunctor, DeriveFoldable, DeriveTraversable, 
             DeriveDataTypeable #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE TemplateHaskell    #-}

module Main (main) where
import           Bound
import           Control.Lens hiding (List)
import           Control.Lens.Plated
import           Data.Deriving (deriveShow1, deriveEq1)
import           Data.Data
import           Data.Data.Lens (uniplate)

data Expr a   = Var   a
              | List  [Expr a]
              | Apply (Expr a) (Expr a)
              | Lam   (Scope () Expr a)
              | Nop
              deriving (Functor, Foldable, Traversable, Data)

main = do
         print ex
         print $ transform removeTest ex

ex :: Expr String
ex = List [Apply (Var "test") $ List [Var "arg1", Var "arg2"]
          ,Apply (Var "two") (Var "three")]

removeTest :: Expr String -> Expr String
removeTest = \expr -> case expr of
                        Apply (Var "test") _ -> Nop
                        _ -> expr

instance Data a => Plated (Expr a) where
  plate = uniplate

makeLenses  ''Expr
makeBound   ''Expr
deriveEq1   ''Expr
deriveShow1 ''Expr
deriving instance Show a => Show (Expr a)
deriving instance Eq   a => Eq   (Expr a)

Conclusion:

List [Apply (Var "test") (List [Var "arg1",Var "arg2"])
     ,Apply (Var "two") (Var "three")]
^CList [Nop,Apply (Var "two") (Var "three")]

---

 -- profiterole stats
 TOT   INH   IND
99.9  99.9    .1  MAIN MAIN (0)


99.9  99.9    .1  MAIN MAIN (0)
99.9  99.9  34.0    Main CAF (0)
65.9  65.9     -      Data.Data.Lens fromOracle (35)
65.9  65.9     -        Data.Data.Lens hitTest (0)
65.9  65.9     -          Data.Data.Lens hitTest.\ (35)
65.9  65.9     -            Data.Data.Lens readCacheFollower (30)
65.9  65.9     -              Data.Data.Lens readCacheFollower.\ (30)
65.9  65.9     -                Data.Data.Lens insertHitMap (1)
65.9  65.9     -                  Data.Data.Lens insertHitMap.populate (1)
65.9  65.9  56.4                    Data.Data.Lens insertHitMap.populate.f (1824891)
 2.3   2.3   2.3                      Data.HashMap.Base clone16 (2682671)
 2.1   2.1   2.1                      Data.HashMap.Base hash (6204631)
 1.7   1.7    .4                      Data.HashMap.Array copy (1620382)
 1.3   1.3   1.3                        Data.HashMap.Array copy.\ (1620382)
 1.1   1.1   1.1                      Data.Data.Lens insertHitMap.populate.fs (2189870)
  .9    .9    .9                      Bound.Var gfoldl (364976)
  .5    .5    .5                      Data.HashMap.Array new_ (810191)
  .5    .5    .5                      Bound.Var gunfold (364976)
  .3    .3    .3                      Data.HashMap.Base sparseIndex (3620621)
  .2    .2    .2                      Bound.Scope gfoldl (182489)

---

Heap Profile:

Answer 1

I will simply answer this: this is a mistake, dfeuer reported this to ekmett/lens.

In the meantime, using tinplateinstead uniplateis a valid workaround.