[GHC] #14309: Expand comment in hPutStrLn

[GHC]

#14309: Expand comment in hPutStrLn
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           Reporter:  dfeuer         |             Owner:  (none)
               Type:  task           |            Status:  new
           Priority:  normal         |         Milestone:  8.4.1
          Component:  Core           |           Version:  8.2.1
  Libraries                          |
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Documentation
  Unknown/Multiple                   |  bug
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 A comment on `hPutStrLn` reads

 > An optimisation: we treat `hPutStrLn` specially, to avoid the
 > overhead of a single `putChar '\n'`, which is quite high now that we
 > have to encode eagerly.

 This should reference some code or comment that explains why the cost is
 high, why we have to encode eagerly, what it even ''means'' to encode
 eagerly, etc.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14309>
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