[GHC] #5218: Add unpackCStringLen# to create Strings from string literals

[GHC]

#5218: Add unpackCStringLen# to create Strings from string literals
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        Reporter:  tibbe             |                Owner:  thoughtpolice
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.0.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #5877 #10064      |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by jscholl):

 Wouldn't that generate something like {{{unpackCString# (# 3#, "abc"#
 #)}}} for {{{"abc"}}}? And if I just typed "abc" in ghci, wouldn't it fail
 as ghci can not handle unboxed tuples? Beside from that, it should work,
 but then I could also just try to change {{{unpackCString#}}} to have type
 {{{Addr# -> Int# -> [Char]}}}, avoiding the tuple. This would of course
 break backwards compatibility, as would an unboxed tuple, and I wanted to
 see if I could avoid that.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5218#comment:43>
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