[GHC] #9077: Forcing the type to be IO {} instead of IO() causes a "panic! The impossible has happened" output.

5 May 2014

      #9077: Forcing the type to be IO {} instead of IO() causes a "panic! The
impossible has happened" output.
-------------------------+-------------------------------------------------
       Reporter:         |             Owner:
  Westycoot              |            Status:  new
           Type:  bug    |         Milestone:
       Priority:         |           Version:  7.8.2
  normal                 |  Operating System:  Unknown/Multiple
      Component:         |   Type of failure:  Compile-time performance bug
  Compiler               |         Test Case:
       Keywords:         |          Blocking:
   Architecture:  x86    |
     Difficulty:         |
  Unknown                |
     Blocked By:         |
Related Tickets:         |
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 Below is the source code in which the bug occurs. It is easily reproduce-
 able, by having the type be IO{} instead of IO().

 When ran, this code will produce the "panic! The impossible has happened"
 output. Which told me to report the bug here.

 By changing IO() to IO{} (which I did by accident), no exception is
 thrown, it simply tells the user to panic!

 {{{
     main :: IO {}
     main = do
             e1 <- getLine
             e2 <- getLine
             print ((read e1) + (read e2))

 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9077
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