[GHC] #12005: Constraint instances not shown in `:info`
#12005: Constraint instances not shown in `:info` -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 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: -------------------------------------+------------------------------------- {{{ $ ghci -ignore-dot-ghci -XKindSignatures -XRank2Types -XConstraintKinds -XAllowAmbiguousTypes -XInstanceSigs GHCi, version 8.1.20160428: http://www.haskell.org/ghc/ :? for help Prelude> import Data.Kind Prelude Data.Kind> class Defer (p :: Constraint) where defer :: (p => r) -> r Prelude Data.Kind> instance Defer () where defer :: r -> r; defer = id Prelude Data.Kind> :i Defer class Defer (p :: Constraint) where defer :: (p => r) -> r {-# MINIMAL defer #-} -- Defined at <interactive>:2:1 }}} Same happens with the [https://github.com/ekmett/constraints/blob/master/src/Data/Constraint/Deferr... Data.Constraint.Deferrable] which defines: {{{#!hs instance (Typeable a, Typeable b) => Deferrable (a ~ b) instance (Deferrable a, Deferrable b) => Deferrable (a, b) instance (Deferrable a, Deferrable b, Deferrable c) => Deferrable (a, b, c) }}} but no instances are shown: {{{ ghci> import Data.Constraint.Deferrable ghci> :i Deferrable class Deferrable (p :: Constraint) where deferEither :: proxy p -> (p => r) -> Either String r {-# MINIMAL deferEither #-} -- Defined in ‘Data.Constraint.Deferrable’ }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12005 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12005: Constraint instances not shown in `:info` -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 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 harpocrates): You may be interested in `:info!` which returns a more reliably complete listing of instances. {{{ Prelude Data.Kind> :i Defer class Defer (p :: Constraint) where defer :: (p => r) -> r {-# MINIMAL defer #-} -- Defined at <interactive>:2:1 instance [safe] Defer (() :: Constraint) -- Defined at <interactive>:3:10 }}} The reason `instance Defer (() :: Constraint)` is filtered out from the output of `:info` is due to `GHC.getInfo`. Unless instructed to not filter its output, this last function will check that //all// names in an instance head are in scope before reporting it. Due to some wrinkles around constraint tuples, `() :: Constraint` doesn't satisfy this check. I consider this a bug. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12005#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12005: Constraint instances not shown in `:info` -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 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):
I consider this a bug.
I think I do too... `()` is really built-in syntax. Would you like to fix it? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12005#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12005: Constraint instances not shown in `:info` -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D5182 Wiki Page: | -------------------------------------+------------------------------------- Changes (by osa1): * status: new => patch * differential: => Phab:D5182 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12005#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12005: Constraint instances not shown in `:info`
-------------------------------------+-------------------------------------
Reporter: Iceland_jack | Owner: (none)
Type: bug | Status: patch
Priority: normal | Milestone:
Component: Compiler | Version: 7.10.3
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s): Phab:D5182
Wiki Page: |
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Comment (by Krzysztof Gogolewski
#12005: Constraint instances not shown in `:info` -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: merge Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D5182 Wiki Page: | -------------------------------------+------------------------------------- Changes (by monoidal): * status: patch => merge -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12005#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#12005: Constraint instances not shown in `:info` -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.6.2 Component: Compiler | Version: 7.10.3 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): Phab:D5182 Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: merge => closed * resolution: => fixed Comment: Merged to `ghc-8.6` with 51c447936ef3f2f3f67c54d2dd62de537f443e89. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12005#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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