Re: [GHC] #12668: Program that fails Core Lint terribly

6 Oct 2016


      #12668: Program that fails Core Lint terribly
-------------------------------------+-------------------------------------
        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Description changed by bgamari:

@@ -21,3 +21,3 @@
- GHC 465c6c5d15f8fb54afb78408f3a79e75e74d2cd4 seems to let this program
- typecheck, but if you enable Core Lint it soon becomes clear that not all
- is well. Here's a sampling of the carnage,
+ GHC 465c6c5d15f8fb54afb78408f3a79e75e74d2cd4 and 8.0.1 seem to let this
+ program typecheck, but if you enable Core Lint it soon becomes clear that
+ not all is well. Here's a sampling of the carnage,

New description:

 While looking for a testcase for another unrelated compiler bug (see
 Phab:D2577) I had the pleasure of encountering this specimen,

 {{{#!hs
 {-# LANGUAGE TypeInType #-}
 {-# LANGUAGE RankNTypes #-}
 module Hi where

 import GHC.Exts

 data Some r = Some (TYPE r -> TYPE r)

 doSomething :: forall (r :: RuntimeRep). forall (a :: TYPE r). ()
             => Int -> (a -> Int) -> a -> a
 doSomething n f =
     case n of
       1 -> error "hello"
       3 -> error "hello"
 }}}

 GHC 465c6c5d15f8fb54afb78408f3a79e75e74d2cd4 and 8.0.1 seem to let this
 program typecheck, but if you enable Core Lint it soon becomes clear that
 not all is well. Here's a sampling of the carnage,
 {{{
 $ ghc hi.hs -fforce-recomp -dcore-lint -O0
 [1 of 1] Compiling Hi               ( hi.hs, hi.o )
 *** Core Lint errors : in result of Desugar (after optimization) ***
 <no location info>: warning:
     In the type ‘a_a2ON -> Int’
     Ill-kinded argument in type or kind ‘a_a2ON -> Int’
     type or kind ‘a_a2ON -> Int’ kind: TYPE r_a2OM
 <no location info>: warning:
     In the type ‘a_a2ON -> a_a2ON’
     Ill-kinded argument in type or kind ‘a_a2ON -> a_a2ON’
     type or kind ‘a_a2ON -> a_a2ON’ kind: TYPE r_a2OM
 <no location info>: warning:
     In the type ‘a_a2ON -> a_a2ON’
     Ill-kinded argument in type or kind ‘a_a2ON -> a_a2ON’
     type or kind ‘a_a2ON -> a_a2ON’ kind: TYPE r_a2OM
 <no location info>: warning:
     In the expression: patError
                          @ 'PtrRepLifted @ (a_a2ON -> a_a2ON)
 "hi.hs:(12,5)-(14,24)|case"#
     Ill-kinded argument in type or kind ‘a_a2ON -> a_a2ON’
     type or kind ‘a_a2ON -> a_a2ON’ kind: TYPE r_a2OM
 ...
 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12668#comment:1
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