[GHC] #13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!hs -- Panic.hs {-# LANGUAGE ApplicativeDo #-} {-# LANGUAGE ExistentialQuantification #-} module Panic where import Data.STRef import Control.Monad.ST data A = forall a. A a st :: ST s () st = do A _ <- pure $ A True ref <- newSTRef 1 readSTRef ref pure () }}} {{{ $ ghc Panic.hs [1 of 1] Compiling Panic ( Panic.hs, Panic.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.1.20170106 for x86_64-unknown-linux): StgCmmEnv: variable not found $dMonad_aGQ local binds for: $trModule $tcA $tc'A $tcA1_rSi $tc'A1_rSJ $trModule1_rSK $trModule2_rSL sat_sT5 sat_sT9 sat_sTa Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable pprPanic, called at compiler/codeGen/StgCmmEnv.hs:137:9 in ghc:StgCmmEnv Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} The above module fails to compile, giving the pasted panic message. Without the ApplicativeDo pragma compilation succeeds. Reproduced with GHC 8.0.2 and a recent head, courtesy of nixpkgs: {{{ gp84vpgar3n3rqvkwj47yyhxvsvbsmi6-ghc-8.1.20170106 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: new Priority: highest | Milestone: Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * priority: normal => highest * owner: => simonmar Comment: Simon M: this is an outright bug somewhere in `ApplicativeDo`. Using `-dcore-lint` nails it immediately in the output of the desugarer: {{{ *** Core Lint errors : in result of Desugar (before optimization) *** <no location info>: warning: In the expression: >>= @ (ST s) $dMonad_aRm @ (STRef s Integer) @ () (newSTRef @ Integer @ s 1) (\ (ref_aFs :: STRef s Integer) -> >> @ (ST s) $dMonad_a12S @ Integer @ () (readSTRef @ s @ Integer ref_aFs) (return @ (ST s) $dMonad_a131 @ () ())) $dMonad_aRm :: Monad m_aRl[tau:3] [LclId] is out of scope <no location info>: warning: In the expression: >>= @ (ST s) $dMonad_aRm @ (STRef s Integer) @ () (newSTRef @ Integer @ s 1) (\ (ref_aFs :: STRef s Integer) -> >> @ (ST s) $dMonad_a12S @ Integer @ () (readSTRef @ s @ Integer ref_aFs) (return @ (ST s) $dMonad_a131 @ () ())) Argument value doesn't match argument type: Fun type: Monad (ST s) => forall a b. ST s a -> (a -> ST s b) -> ST s b Arg type: Monad m_aRl[tau:3] Arg: $dMonad_aRm *** Offending Program *** Rec { $tcA :: TyCon [LclIdX] $tcA = TyCon 4740327979976134328## 15826189822472469109## $trModule (TrNameS "A"#) $tc'A :: TyCon [LclIdX] $tc'A = TyCon 9840332441209672147## 16375955839481284679## $trModule (TrNameS "'A"#) $trModule :: Module [LclIdX] $trModule = Module (TrNameS "main"#) (TrNameS "T13242"#) st :: forall s. ST s () [LclIdX] st = \ (@ s_aQu) -> let { $dApplicative_aR0 :: Applicative (ST s) [LclId] $dApplicative_aR0 = $fApplicativeST @ s } in let { $dApplicative_aR7 :: Applicative (ST s) [LclId] $dApplicative_aR7 = $dApplicative_aR0 } in let { $dFunctor_aQK :: Functor (ST s) [LclId] $dFunctor_aQK = $fFunctorST @ s } in <*> @ (ST s) $dApplicative_aR0 @ () @ () (fmap @ (ST s) $dFunctor_aQK @ A @ (() -> ()) (\ (ds_d13u :: A) (ds_d13v :: ()) -> case ds_d13u of wild_00 { A @ a_aRa ds_d13w -> let { $dNum_a12O :: Num Integer [LclId] $dNum_a12O = $fNumInteger } in let { $dMonad_aRm :: Monad (ST s) [LclId] $dMonad_aRm = $fMonadST @ s } in let { $dMonad_a12S :: Monad (ST s) [LclId] $dMonad_a12S = $dMonad_aRm } in let { $dMonad_a131 :: Monad (ST s) [LclId] $dMonad_a131 = $dMonad_aRm } in let { ds_d13x :: () [LclId] ds_d13x = ds_d13v } in case ds_d13x of wild_00 { () -> () } }) ($ @ 'LiftedRep @ A @ (ST s A) (pure @ (ST s) $dApplicative_aR7 @ A) (A @ Bool True))) (>>= @ (ST s) $dMonad_aRm @ (STRef s Integer) @ () (newSTRef @ Integer @ s 1) (\ (ref_aFs :: STRef s Integer) -> >> @ (ST s) $dMonad_a12S @ Integer @ () (readSTRef @ s @ Integer ref_aFs) (return @ (ST s) $dMonad_a131 @ () ()))) end Rec } }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: new Priority: highest | Milestone: 8.0.3 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * milestone: => 8.0.3 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: new Priority: highest | Milestone: 8.0.3 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonmar): smaller example: {{{ data A = forall a. A a st :: IO () st = do A _ <- pure (A True) x <- return 1 pure () }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: new Priority: highest | Milestone: 8.0.3 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonmar): @simonpj I've investigated this and run into something I don't understand, can you help? When we typecheck the above program without `ApplicativeDo` we get {{{ AbsBindsSig [] [] {Exported type: st :: IO () [LclId] Bind: st_aNk = do A{a_aNN EvBinds{[W] $dMonad_aNP = $dMonad_aNw [W] $dMonad_aNU = $dMonad_aNw [W] $dMonad_aZe = $dMonad_aNw [W] $dNum_aZc = GHC.Num.$fNumInteger @[] []}} _ <- pure @ IO $dApplicative_aNK @ A (A @ Bool True) x_aCp <- return @ IO $dMonad_aNU @ Integer 1 return @ IO $dMonad_aZe @ () () Evidence: EvBinds{}} }}} Note that `$dMonad_aNU`, used in the second statement, is bound by the `EvBinds` in the (existential) pattern in the first statement. ApplicativeDo isn't expecting there to be any dependencies between the two patterns, which is why it produces invalid Core. I don't understand why we're putting these dict bindings in the first pattern, they don't seem to relate to the existential type. I could just disable ApplicativeDo for existential patterns, but if that's necessary I'd like to understand why. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: new Priority: highest | Milestone: 8.0.3 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by rwbarton): Summary of the discussion of this ticket at today's meeting: * When we type check (in `tcApplicativeStmts`) a group of independent statements {{{#!hs do pat1 <- exp1 pat2 <- exp2 ... patN <- expN }}} stuff bound by `pat1` should ''not'' be visible in `exp2`, and so on. Here stuff includes both the (visible) values bound by `pat1`, and also (invisible) dictionaries or equality constraints bound by matching on a qualified or GADT constructor. However, ''all'' the stuff (both visible and invisible) bound by any of the patterns should be in scope after the group. * We decided how to split a `do` expression into groups of independent statements earlier, in the renamer, on syntactic grounds; that is, based only on ''visible'' stuff. But there could be invisible dependencies too, such as in {{{#!hs {-# LANGUAGE GADTs #-} {-# LANGUAGE ApplicativeDo #-} module T12870 where data T a = Eq a => T f :: (Monad m) => a -> a -> m (T a) -> (Bool -> m b) -> m (b, b) f x y mta mb = do T <- mta r1 <- mb (x == y) r2 <- mb (x == y) return (r1, r2) }}} This program compiles today without `ApplicativeDo`, but causes the panic discussed here with `ApplicativeDo`. In the current scheme we determine the groups of independent statements in the renamer, which is too early to detect that the expression `mb (x == y)` relies on the binding of `T`. Plus Simon thinks it would be too fragile anyways. (What if there was another `Eq a` instance in scope from somewhere else? Which instance do we use? It would affect the grouping.) Simon's suggestion was to reject a program like this in the type checking stage. It would be a bit unfortunate, because the program would have compiled fine without `ApplicativeDo`. Here's another suggestion: whenever there is a pattern match that binds invisible stuff, just assume that that stuff is used in all following statements. Similar to "just disable ApplicativeDo for existential patterns", but the issue isn't existentials, but rather dictionaries or equality constraints. The original program using `data A = forall a. A a` is actually fine to treat as a single group of independent statements, since the pattern match on `A _` doesn't bind any invisible stuff. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: new Priority: highest | Milestone: 8.0.3 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Simon I have realised another problem with `ApplicativeDo`, not covered by our paper. Consider {{{ data A where A :: a -> (a->Int) -> A st :: A -> A -> IO (Int,Int) st p q = do p1 <- pure p A x1 f1 <- pure p1 q1 <- pure q A x2 f2 <- pure q1 pure (f1 x1, f2 x2) }}} We'll try to gather `(x1,f1)` in a pair, and `(x2,f2)`; but that won't work because they each mention an existential type variable. Our desugaring just doesn't work at all for that case. What to do? Another awkward wrinkle: what are the dependencies induced by view patterns? And do we account for them? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: new Priority: highest | Milestone: 8.0.3 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonmar): @simonpj One position is to say that it should typecheck if the desugaring (according to the paper) is type-correct, which in this case it isn't. And in fact I think that's what happens: {{{ do1.hs:12:8: error: • Couldn't match expected type ‘t0’ with actual type ‘(a -> Int, a)’ because type variable ‘a’ would escape its scope This (rigid, skolem) type variable is bound by a pattern with constructor: A :: forall a. a -> (a -> Int) -> A, in a pattern binding in 'do' block at ado1.hs:12:3-9 • In the pattern: (f1, x1) In the expression: do { p1 <- pure p; A x1 f1 <- pure p1; q1 <- pure q; A x2 f2 <- pure q1; return (f1 x1, f2 x2) } In an equation for ‘st’: st p q = do { p1 <- pure p; A x1 f1 <- pure p1; q1 <- pure q; A x2 f2 <- pure q1; return (f1 x1, f2 x2) } • Relevant bindings include f1 :: a -> Int (bound at ado1.hs:12:8) x1 :: a (bound at ado1.hs:12:5) }}} Arguably we should do something more clever, but at least it's sound. So I'm less worried about this case than the original one which typechecks but generates invalid Core. I'll investigate to see if I can make it typecheck the rhs's separately from the patterns. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: new Priority: highest | Milestone: 8.0.3 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): OK here's what I can do easily. Let's say that in a `Stmt` {{{ pat <- rhs }}} * the `Stmt` ''requires'' constraints needed to typecheck `rhs`, and to pattern-match `pat` (e.g. in a view pattern) * the `Stmt` ''binds'' the existential type variables and constraints brought into scope by the pattern `pat` So for example, given {{{ data T a where MkT :: (Eq a, Show b) => a -> b -> T a }}} Suppose that `v :: t` is in scope. Then the stmt {{{ MkT 1 x <- (...show v...) :: T t }}} * requires `Show t` (from the use of `show`) and `Num t` (from the literal `1`). * binds the existential `b` and constraint `Show b`. Now consider {{{ ...stmts... ApplicativeStmts [arg1, arg2, ... argN] ...more stmts... }}} where `argi :: ApplicativeArg`. Each `argi` itself contains one or more `Stmts`. It is easy to ensure that * Constraints required by the `argi` can be solved from constraint bound by `...stmts...` * Constraints and existentials bound by the `argi` are not available to solve constraints required either by `argj` (where i is different from j), or by `...more stmts...`. * Within the stmts of each `argi` individually, constraints bound by earlier stmts can be used to solve later ones. That is easy to implement and solves the immediate problem. I'm validating now. ------------------------ But the rule is terribly unsatisfactory. * To typecheck the program you must mentally desugar it into its applicative groups. * If you write {{{ MkT x1 _ <- rhs1 MkT x2 _ <- rhs2 }}} you really might intend that the `Eq t` bound by the first stmt is available to solve requirements of `rhs2`. And with normal monadic deguaring it would be, but not with `ApplicativeDo`. Worse, ''there is no way to fix it'' becuase `ApplicativeDo` works module-wide. My solution is: add syntax to allow the programmer to express the program in the form of Figure 2 of our paper, that is, post-rearrangement. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: new Priority: highest | Milestone: 8.0.3 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Simon, I also want to discuss the implementation. Look at `goArgs` in `tcApplicativeStmts`. It uses a CPS structure, so that things brought into scope stay in scope. But that's wrong for constraints (hence this ticket), and it's not really right for bindings either (only the `thing_inside` needs to see those binders). So, proposal: * Use a `mapM` to process each of the args indepdendly (mirroring the intended parallel semantics) * Now bring into scope all the variables bound by the args (which we can get from their patterns), and typecheck `thing_inside`. Can you see anything wrong with this? Should not be hard to try. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and
ExistentialQuantification
-------------------------------------+-------------------------------------
Reporter: ljli | Owner: simonmar
Type: bug | Status: new
Priority: highest | Milestone: 8.0.3
Component: Compiler | Version: 8.1
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
-------------------------------------+-------------------------------------
Comment (by Simon Peyton Jones
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: new Priority: highest | Milestone: 8.0.3 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonmar):
But the rule is terribly unsatisfactory.
Yes it is. I think I'd also be fine with disabling ApplicativeDo for all statements following an existential pattern match. Or perhaps @rwbarton's suggestion:
whenever there is a pattern match that binds invisible stuff, just assume that that stuff is used in all following statements
But by itself this doesn't solve the problem that the example in this ticket raises, because the A type doesn't bind any dictionaries or constraints. By all means refactor the implementation of `tcApplicativeStmts`! Provided the tests pass it should be fine. I remember trying quite hard to simplify the implementation to use fewer fresh type variables, but I couldn't figure out how to do it. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: new Priority: highest | Milestone: 8.0.3 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonmar): @simonpj Could you explain why you needed to fiddle with the LIE? I thought it would be sufficient to typecheck each statement (group) separately rather than typechecking later statements inside the scope of previous ones. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
I thought it would be sufficient to typecheck each statement (group) separately rather than typechecking later statements inside the scope of
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: new Priority: highest | Milestone: 8.0.3 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): previous ones. Yes; that's what I meant by comment:9. seems to work, and much simpler. Validating now. Re unsatisfactory nature of the current story: I'll leave it to you to document the behaviour, and perhaps improve it along the lines you suggest. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and
ExistentialQuantification
-------------------------------------+-------------------------------------
Reporter: ljli | Owner: simonmar
Type: bug | Status: new
Priority: highest | Milestone: 8.0.3
Component: Compiler | Version: 8.1
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
-------------------------------------+-------------------------------------
Comment (by Simon Peyton Jones
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: new Priority: highest | Milestone: 8.0.3 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Assigning to simonmar for user-manual updates; and possible further work on the design. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: new Priority: highest | Milestone: 8.0.3 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonmar): @simonpj, so the new code doesn't bring constraints into scope from existential bindings, even in statements that sequentially follow the existential pattern match. e.g. {{{ Prelude> data T where A :: forall a . Eq a => a -> T Prelude> :set -XApplicativeDo Prelude> do { A x <- undefined; y <- return (); return (x == x) } <interactive>:7:48: error: • Could not deduce (Eq a) arising from a use of ‘==’ from the context: Monad f bound by the inferred type of it :: Monad f => f Bool at <interactive>:7:1-56 Possible fix: add (Eq a) to the context of the inferred type of it :: Monad f => f Bool • In a stmt of a 'do' block: return (x == x) In the expression: do A x <- undefined y <- return () return (x == x) In an equation for ‘it’: it = do A x <- undefined y <- return () return (x == x) }}} I understand why - because the implementation specifically only binds Ids - but it's somewhat surprising. Is this fixable, or should I try to document it? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: new Priority: highest | Milestone: 8.0.3 Component: Compiler | Version: 8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj):
Is this fixable, or should I try to document it?
The latter I think. It's hard to fix: just try to write the desugaring!! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and
ExistentialQuantification
-------------------------------------+-------------------------------------
Reporter: ljli | Owner: simonmar
Type: bug | Status: new
Priority: highest | Milestone: 8.2.1
Component: Compiler | Version: 8.1
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
-------------------------------------+-------------------------------------
Comment (by Simon Marlow
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: closed Priority: highest | Milestone: 8.2.1 Component: Compiler | Version: 8.1 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonmar): * status: new => closed * resolution: => fixed -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:20 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and ExistentialQuantification -------------------------------------+------------------------------------- Reporter: ljli | Owner: simonmar Type: bug | Status: closed Priority: highest | Milestone: 8.2.1 Component: Compiler | Version: 8.1 Resolution: fixed | Keywords: ApplicativeDo Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * keywords: => ApplicativeDo -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13242#comment:21 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#13242: Panic "StgCmmEnv: variable not found" with ApplicativeDo and
ExistentialQuantification
-------------------------------------+-------------------------------------
Reporter: ljli | Owner: simonmar
Type: bug | Status: closed
Priority: highest | Milestone: 8.2.1
Component: Compiler | Version: 8.1
Resolution: fixed | Keywords: ApplicativeDo
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
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Comment (by Ben Gamari
participants (1)
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