[GHC] #15232: TypeError is reported as "redundant constraint" starting with GHC 8.2
#15232: TypeError is reported as "redundant constraint" starting with GHC 8.2 -------------------------------------+------------------------------------- Reporter: fsoikin | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.2.3 Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Unknown/Multiple CustomTypeErrors | Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following program compiles fine on GHC 8.0.2, but GHC 8.2.2 issues a warning, complaining that `TypeError` is a redundant constraint. This makes it very inconvenient to use `TypeError` with type classes. {{{#!hs {-# OPTIONS_GHC -Wredundant-constraints -Wall -Werror #-} import GHC.TypeLits (TypeError, ErrorMessage(..)) class C a where f :: a -> a instance {-# OVERLAPPING #-} C Int where f _ = 42 instance {-# OVERLAPPABLE #-} TypeError ( 'Text "Only Int is supported" ) => C a where f = undefined main :: IO () main = print $ f (42::Int) }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15232 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#15232: TypeError is reported as "redundant constraint" starting with GHC 8.2
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Reporter: fsoikin | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone: 8.2.3
Component: Compiler | Version: 8.2.2
Resolution: | Keywords:
| CustomTypeErrors
Operating System: Unknown/Multiple | Architecture:
Type of failure: Incorrect | Unknown/Multiple
error/warning at compile-time | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
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Comment (by Ben Gamari
#15232: TypeError is reported as "redundant constraint" starting with GHC 8.2
-------------------------------------+-------------------------------------
Reporter: fsoikin | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone: 8.2.3
Component: Compiler | Version: 8.2.2
Resolution: | Keywords:
| CustomTypeErrors
Operating System: Unknown/Multiple | Architecture:
Type of failure: Incorrect | Unknown/Multiple
error/warning at compile-time | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
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Comment (by Ben Gamari
#15232: TypeError is reported as "redundant constraint" starting with GHC 8.2 -------------------------------------+------------------------------------- Reporter: fsoikin | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 Resolution: fixed | Keywords: | CustomTypeErrors Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple error/warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: new => closed * resolution: => fixed * milestone: 8.2.3 => 8.6.1 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15232#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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