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Unsound type
Related to #12
The same wrapping trick can get us an unsound type.
In the following we show that Char 'a' can be unsafely cast to Int 97.
Changing Int to (Int,Int) causes a seg fault.
Nick
{-#LANGUAGE ExistentialQuantification, RankNTypes #-}
module Main(main) where
import Data.HMap(HKey,HMap)
import qualified Data.HMap as HMap
data Wrapped a = forall x. Wrap (HKey x a)
w :: Wrapped a
w = HMap.withKey Wrap
hmap :: HMap
hmap = case w of Wrap k -> HMap.insert k 'a' HMap.empty
res :: Maybe Int -- replace Int with (Int,Int) for seg fault!
res = case w of Wrap k -> HMap.lookup k hmap
main :: IO ()
main = do
print res
{- Prints...
Just 97
-}
Implicit use of weak pointers causing memory issues
Hi!
Why is this library using weak pointers, from key to value?
When we add values to a map, there is no option to remove them from memory and they are stuck there until the key is deleted too. There are many use cases that you cannot remove the key (e.g updating value in a map) and need your app not too eat all the RAM.
Loss of referential transparency
The doc for HKey.withKey states:
"The implementation actually creates a key, but because the key cannot escape the given function f, there is no way to observe that if we run withKey f twice, that it will get a different key the second time."
But in the following we see it is possible.
Nick
{-#LANGUAGE ExistentialQuantification, RankNTypes #-}
module Main(main) where
import Data.HMap as HMap
data Wrapped = forall x. Wrapped (HKey x ())
create :: () -> Wrapped
create () = HMap.withKey Wrapped
x,y,z :: Wrapped
x = create ()
y = create ()
z = y
comp :: Wrapped -> Wrapped -> Bool
comp (Wrapped key1) (Wrapped key2) = HMap.unique key1 == HMap.unique key2
main :: IO ()
main = do
print ("x~y",comp x y)
print ("x~z",comp x z)
print ("y~z",comp y z)
{- Prints...
("x~y",False)
("x~z",False)
("y~z",True)
-}
Not in scope: type constructor or class ‘Foldable’
Hi! It looks like master version have some compile issues
Resolving dependencies...
Notice: installing into a sandbox located at
/home/pmlodawski/dev/projects/HMap/.cabal-sandbox
Configuring text-1.2.1.1...
Configuring transformers-0.4.3.0...
Building text-1.2.1.1...
Building transformers-0.4.3.0...
Installed transformers-0.4.3.0
Configuring mtl-2.2.1...
Building mtl-2.2.1...
Installed mtl-2.2.1
Installed text-1.2.1.1
Configuring hashable-1.2.3.2...
Building hashable-1.2.3.2...
Installed hashable-1.2.3.2
Configuring unordered-containers-0.2.5.1...
Building unordered-containers-0.2.5.1...
Installed unordered-containers-0.2.5.1
Configuring HMap-1.2.3...
Building HMap-1.2.3...
Failed to install HMap-1.2.3
Build log ( /home/pmlodawski/dev/projects/HMap/.cabal-sandbox/logs/HMap-1.2.3.log ):
Configuring HMap-1.2.3...
Building HMap-1.2.3...
Preprocessing library HMap-1.2.3...
[1 of 6] Compiling Data.HideType ( Data/HideType.hs, dist/dist-sandbox-47edc933/build/Data/HideType.o )
[2 of 6] Compiling Data.HKeyPrivate ( Data/HKeyPrivate.hs, dist/dist-sandbox-47edc933/build/Data/HKeyPrivate.o )
[3 of 6] Compiling Data.Untypeable ( Data/Untypeable.hs, dist/dist-sandbox-47edc933/build/Data/Untypeable.o )
[4 of 6] Compiling Data.HKey ( Data/HKey.hs, dist/dist-sandbox-47edc933/build/Data/HKey.o )
[5 of 6] Compiling Data.HMap ( Data/HMap.hs, dist/dist-sandbox-47edc933/build/Data/HMap.o )
[6 of 6] Compiling Data.HKeySet ( Data/HKeySet.hs, dist/dist-sandbox-47edc933/build/Data/HKeySet.o )
Data/HKeySet.hs:75:11:
Not in scope: type constructor or class ‘Foldable’
cabal: Error: some packages failed to install:
HMap-1.2.3 failed during the building phase. The exception was:
ExitFailure 1
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