[GHC] #10009: type inference regression when faking injective type families

[GHC]

#10009: type inference regression when faking injective type families
-------------------------------------+-------------------------------------
        Reporter:  aavogt            |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  high              |               Milestone:  7.10.2
       Component:  Compiler (Type    |                 Version:  7.10.1-rc1
  checker)                           |                Keywords:
      Resolution:                    |            Architecture:
Operating System:  Unknown/Multiple  |  Unknown/Multiple
 Type of failure:  GHC rejects       |               Test Case:
  valid program                      |                Blocking:
      Blocked By:                    |  Differential Revisions:
 Related Tickets:  #10226            |
-------------------------------------+-------------------------------------
Changes (by adamgundry):

 * milestone:  7.12.1 => 7.10.2


Comment:

 Any chance we can get this addressed for 7.10.2? It's a definite failure
 of completeness in the constraint solver that is a regression from 7.8 and
 is affecting code in the wild. It is possible to rewrite affected code
 using proxies, but only with fairly invasive changes. As Edsko noted,
 adding type signatures is not necessarily enough.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10009#comment:20>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler