[GHC] #10004: rec {} causes "head:empty list" exception

19 Jan 2015


      #10004: rec {} causes "head:empty list" exception
-------------------------------------+-------------------------------------
              Reporter:  alanz       |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.11
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |        Blocked By:
             Test Case:              |   Related Tickets:
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------
 Using GHC HEAD 7.11.20150116 (and before)

 Trying to load the following into ghci

 {{{#!hs
 {-# LANGUAGE RecursiveDo #-}

 bar :: IO ()
 bar = do
   rec {}
   return ()
 }}}

 results in

 {{{
...
:load "/home/alanz/mysrc/github/alanz/ghc-
 exactprint/tests/examples/Foo.hs"
 [1 of 1] Compiling Main             ( /home/alanz/mysrc/github/alanz/ghc-
 exactprint/tests/examples/Foo.hs, interpreted )
 *** Exception: Prelude.head: empty list
}}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10004
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