[GHC] #12373: Type error but types match

7 Jul 2016

      #12373: Type error but types match
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           Reporter:  osa1           |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.1
  (Type checker)                     |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 {{{
...
unboxedsums git:(prim_sums_rebase_5) x cat primop_bug.hs
 {-# LANGUAGE MagicHash, ScopedTypeVariables, UnboxedTuples #-}
module Main where

 import GHC.MVar
 import GHC.Prim
 import GHC.Types

 main :: IO ()
 main = IO (\rw -> newMVar# rw) >> return ()
...
unboxedsums git:(prim_sums_rebase_5) x ghc-stage1 primop_bug.hs -ddump-
 stg -ddump-cmm -ddump-to-file -fforce-recomp -dumpdir primop_fails -O
 -fprint-explicit-kinds
 [1 of 1] Compiling Main             ( primop_bug.hs, primop_bug.o )
primop_bug.hs:10:19: error:
     • Couldn't match a lifted type with an unlifted type
       Expected type: (# State# RealWorld, MVar# RealWorld a0 #)
         Actual type: (# State# RealWorld, MVar# RealWorld a0 #)
     • In the expression: newMVar# rw
       In the first argument of ‘IO’, namely ‘(\ rw -> newMVar# rw)’
       In the first argument of ‘(>>)’, namely ‘IO (\ rw -> newMVar# rw)’
 }}}

 Tried with HEAD, 8.0.1.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12373
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