[GHC] #9236: hGetContents leads to late/silent failures

[GHC]

#9236: hGetContents leads to late/silent failures
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       Reporter:  dfeuer            |             Owner:
           Type:  feature request   |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  Compiler          |           Version:  7.6.3
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 A common newbie error:
 {{{
 #!haskell
 withFile "file" ReadMode hGetContents >>= putStr
 }}}

 The problem, of course, is that the result of `withFile "file" ReadMode
 hGetContents` isn't forced until `putStr` is executed, at which point the
 file has already been closed. The Haskell report doesn't specify what it
 will find, and, at least in 7.6.3, it finds the string empty. The behavior
 that seems most correct to me would be to guarantee that if a file has not
 been completely read (or read up to an I/O error) when it is closed, then
 its contents should be reported as something like `"Four score and seven
 years ag"++error "Forcing a suspended computation led to an attempted read
 from a handle that was already closed."` Since the current system
 apparently puts an `[]` as a temporary marker while waiting to see what
 the rest of the list will be, I imagine that the fix is as simple as
 putting the error thunk there instead.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9236>
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