#2182: ghc sessions (--make, --interactive, ghc api) erroneously retain instances -------------------------------------+------------------------------------- Reporter: claus | Owner: Type: bug | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler | Version: 6.9 (Type checker) | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: GHC | Related Tickets: accepts invalid program | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Changes (by ezyang): * priority: low => normal * failure: None/Unknown => GHC accepts invalid program * component: GHCi => Compiler (Type checker) * milestone: ⊥ => 7.10.1 Old description:

{{{ $ compiler/stage2/ghc-inplace --interactive GHCi, version 6.9.20080317: http://www.haskell.org/ghc/ :? for help Loading package base ... linking ... done. Prelude> :i Functor class Functor f where fmap :: (a -> b) -> f a -> f b -- Defined in GHC.Base instance Functor Maybe -- Defined in Data.Maybe instance Functor [] -- Defined in GHC.Base instance Functor IO -- Defined in GHC.IOBase Prelude> fmap not (True,True)

<interactive>:1:0: No instance for (Functor ((,) Bool)) arising from a use of `fmap' at <interactive>:1:0-19 Possible fix: add an instance declaration for (Functor ((,) Bool)) In the expression: fmap not (True, True) In the definition of `it': it = fmap not (True, True) Prelude> :m +Data.Array Prelude Data.Array> :i Functor class Functor f where fmap :: (a -> b) -> f a -> f b -- Defined in GHC.Base instance (Ix i) => Functor (Array i) -- Defined in GHC.Arr instance Functor ((->) r) -- Defined in Control.Monad.Instances instance Functor ((,) a) -- Defined in Control.Monad.Instances instance Functor (Either a) -- Defined in Control.Monad.Instances instance Functor Maybe -- Defined in Data.Maybe instance Functor [] -- Defined in GHC.Base instance Functor IO -- Defined in GHC.IOBase Prelude Data.Array> fmap not (True,True) (True,False) Prelude Data.Array> :m -Data.Array Prelude> :i Functor class Functor f where fmap :: (a -> b) -> f a -> f b -- Defined in GHC.Base instance Functor ((->) r) -- Defined in Control.Monad.Instances instance Functor ((,) a) -- Defined in Control.Monad.Instances instance Functor (Either a) -- Defined in Control.Monad.Instances instance Functor Maybe -- Defined in Data.Maybe instance Functor [] -- Defined in GHC.Base instance Functor IO -- Defined in GHC.IOBase Prelude> fmap not (True,True) (True,False) }}}

New description: The EPS (external-package state) is only ever increased, never decreased between compilation of different modules in a single batch compilation or GHCi session. Example 1 (GHCi): {{{ ezyang@sabre:~/Dev/labs/ezyangest$ ghci GHCi, version 7.6.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Prelude> (\x -> x) <interactive>:2:1: No instance for (Show (t0 -> t0)) arising from a use of `print' Possible fix: add an instance declaration for (Show (t0 -> t0)) In a stmt of an interactive GHCi command: print it Prelude> :m +Text.Show.Functions Prelude Text.Show.Functions> (\x -> x) <function> Prelude Text.Show.Functions> :m -Text.Show.Functions Prelude> :r Ok, modules loaded: none. Prelude> (\x -> x) <function> }}} Example 2 (make): {{{ ezyang@sabre:~/Dev/labs/ezyangest$ cat A.hs module A where import Text.Show.Functions ezyang@sabre:~/Dev/labs/ezyangest$ cat B.hs module B where y = show (\x -> x) ezyang@sabre:~/Dev/labs/ezyangest$ ghc --make B.hs A.hs [1 of 2] Compiling A ( A.hs, A.o ) [2 of 2] Compiling B ( B.hs, B.o ) ezyang@sabre:~/Dev/labs/ezyangest$ ghc --make A.hs B.hs -fforce-recomp [1 of 2] Compiling B ( B.hs, B.o ) B.hs:2:5: No instance for (Show (t0 -> t0)) arising from a use of `show' Possible fix: add an instance declaration for (Show (t0 -> t0)) In the expression: show (\ x -> x) In an equation for `y': y = show (\ x -> x) }}} -- Comment: I updated the bug description with some modernized, simpler test-cases. simonpj and I have chatted about this and we have a new, improved plan of attack to solve the problem: 1. We'll maintain a set of loaded interface files in the type-checking environment. When an interface file is loaded, we add it to this set. 2. When a type class instance lookup is performed, IF the instance is an orphan, we'll also check if the interface file which defined the instance is in the loaded set. If it is not, we pretend it doesn't exist. I have most of a patch to solve this but I have to shake out a bug where GHCi is not preserving the set of loaded interfaces. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/2182#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler