[GHC] #9398: Data.List.cycle is not a good producer

[GHC]

#9398: Data.List.cycle is not a good producer
-------------------------------------+-------------------------------------
              Reporter:  dfeuer      |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:  7.8.4
             Component:              |          Version:  7.8.3
  libraries/base                     |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Easy (less than 1
  Unknown/Multiple                   |  hour)
       Type of failure:  Runtime     |       Blocked By:
  performance bug                    |  Related Tickets:
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------

Comment (by isaacdupree):

 In compiled code, the latter definition throws <<loop>>, which is nice.
 Try `runghc test.hs` (nontermination) vs `ghc test.hs && ./test`
 (exception):

 {{{
 import GHC.Exts

 cycle2 xs = build $ \c _ ->  let cyc = foldr c cyc xs in cyc

 main = print (cycle2 [] !! 0 :: Int)
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9398#comment:14>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler