[GHC] #10619: Order matters when type-checking
#10619: Order matters when type-checking -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- When I say {{{ {-# LANGUAGE RankNTypes #-} module Bug where foo True = (\x -> x) :: (forall a. a -> a) -> forall b. b -> b foo False = \y -> y }}} the module compiles. But when I say {{{ {-# LANGUAGE RankNTypes #-} module Bug where foo False = \y -> y foo True = (\x -> x) :: (forall a. a -> a) -> forall b. b -> b }}} it doesn't, failing with {{{ Bug.hs:6:13: Couldn't match type ‘b0 -> b0’ with ‘forall a. a -> a’ Expected type: (forall a. a -> a) -> forall a. a -> a Actual type: (forall a. a -> a) -> b0 -> b0 In the expression: (\ x -> x) :: (forall a. a -> a) -> forall b. b -> b In an equation for ‘foo’: foo True = (\ x -> x) :: (forall a. a -> a) -> forall b. b -> b }}} I believe this behavior stems from the special case in `tcMonoBinds`, for non-recursive functions without a type signature. I believe the bug would be fixed if that function also checks to make sure that there is precisely one clause to the function. Do you agree? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10619 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10619: Order matters when type-checking -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by goldfire): It gets worse. The same problem happens between these two: This succeeds: {{{ {-# LANGUAGE RankNTypes #-} module Bug where foo _ = if True then ((\x -> x) :: (forall a. a -> a) -> forall b. b -> b) else \y -> y }}} This fails: {{{ foo _ = if True then \y -> y else ((\x -> x) :: (forall a. a -> a) -> forall b. b -> b) }}} But the cause is different. This second case is caused by the fact that `ReturnTv`s can unify with polytypes, and the `ReturnTv` for the whole expression is just pushed into the `if`'s branches. But even if the `ReturnTv` were replaced by a `TauTv` before pushing into the `if`'s branches, it would ''still'' be broken because a `TauTv` with an !OpenKind can also unify with polytypes. I think the solution for this case is to create a new flavor of `TauTv` that truly insists on being a tau-type. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10619#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10619: Order matters when type-checking -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by jstolarek): * cc: jstolarek (added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10619#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10619: Order matters when type-checking
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Reporter: goldfire | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.10.1
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
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Comment (by Richard Eisenberg
#10619: Order matters when type-checking
-------------------------------------+-------------------------------------
Reporter: goldfire | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.10.1
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
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Comment (by Richard Eisenberg
#10619: Order matters when type-checking -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | typecheck/should_fail/T10619 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by goldfire): * testcase: => typecheck/should_fail/T10619 * status: new => closed * resolution: => fixed -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10619#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#10619: Order matters when type-checking -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 7.10.1 Resolution: fixed | Keywords: | ImpredicativeTypes Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | typecheck/should_fail/T10619 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * keywords: => ImpredicativeTypes -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10619#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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