[GHC] #9795: Debug.Trace.trace is too strict

[GHC]

#9795: Debug.Trace.trace is too strict
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              Reporter:  jcpetruzza  |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:              |          Version:  7.8.3
  libraries/base                     |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Comment (by jcpetruzza):

 As another example of why `trace` shouldn't be strict, consider the
 following:

 {{{#!hs
 f xs = trace (show xs) $ g 0 xs
   where
     g n []     = n
     g n (x:xs) = g (n+1) xs

 main
   = print $ f [1..]
 }}}

 Because `trace` is strict, no output will be shown, which hides the fact
 that `f` is actually being called but with invalid input.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9795#comment:1>
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