[GHC] #14045: Data family instances must list all patterns of family, despite documentation's claims to the contrary

GHC ghc-devs at haskell.org
Mon Jul 31 12:34:12 UTC 2017


#14045: Data family instances must list all patterns of family, despite
documentation's claims to the contrary
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.3
  checker)                           |
      Resolution:                    |             Keywords:  TypeFamilies
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  GHC rejects       |            Test Case:  indexed-
  valid program                      |  types/should_compile/T14045,
                                     |  indexed-types/should_fail/T14045a
      Blocked By:                    |             Blocking:
 Related Tickets:  #12369            |  Differential Rev(s):  Phab:D3804
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by goldfire):

 Does that do it? It's all in `Note [Arity of data families]` in
 FamInstEnv.

 Also, the skipped arity check in the previous patch is in `tc_fam_ty_pats`
 in TcTyClsDecls.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14045#comment:10>
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