Yes, but it is not feasible before GHC 8.6, due to needing GHC >= 8.2 for bootstrapping.

True.  But 8.4 will fork off shortly; so once that is done, we are happy with perf, we can add the change to master in preparation for 8.6.

Simon

From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Alan & Kim Zimmerman
Sent: 22 November 2017 13:30
To: ghc-devs@haskell.org
Subject: Re: [GHC] #14490: TTG Snags

Yes, but it is not feasible before GHC 8.6, due to needing GHC >= 8.2 for bootstrapping.

On 22 November 2017 at 15:26, GHC <ghc-devs@haskell.org> wrote:

#14490: TTG Snags
-------------------------------------+-------------------------------------
        Reporter:  alanz             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14482            |  Differential Rev(s):
       Wiki Page:                    |
  ImplementingTreesThatGrow          |
-------------------------------------+-------------------------------------

Comment (by Shayan-Najd):

 > So making a Data instance per concrete version may be the best way to
 go. Plan B.

 Regardless of the GHC version we use, the question is whether Plan B
 really fixes the build-time problem. Can we test it?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14490#comment:31>

GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler