[GHC] #13154: Standalone-derived anyclass instances aren't as permissive as empty instances
GHC
ghc-devs at haskell.org
Mon Jan 22 20:54:17 UTC 2018
#13154: Standalone-derived anyclass instances aren't as permissive as empty
instances
-------------------------------------+-------------------------------------
Reporter: RyanGlScott | Owner: RyanGlScott
Type: bug | Status: patch
Priority: normal | Milestone: 8.6.1
Component: Compiler (Type | Version: 8.1
checker) |
Resolution: | Keywords: deriving
Operating System: Unknown/Multiple | Architecture:
Type of failure: GHC rejects | Unknown/Multiple
valid program | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s): Phab:D4337
Wiki Page: |
-------------------------------------+-------------------------------------
Changes (by RyanGlScott):
* status: new => patch
* differential: => Phab:D4337
Comment:
Phab:D4337 fixes the issue in comment:8. It does //not// fix the entire
issue, as there is still the degenerate case of:
{{{#!hs
{-# LANGUAGE DeriveAnyClass #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE StandaloneDeriving #-}
class C a
deriving instance C a
}}}
Which needs further patching to fix.
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13154#comment:13>
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