[GHC] #1683: strange MVar / UnsafePerformIO (and type checker...) behaviour

[GHC]

#1683: strange MVar / UnsafePerformIO (and type checker...) behaviour
---------------------------------------------------+------------------------
    Reporter:  komuves at renyi.hu                    |        Owner:         
        Type:  bug                                 |       Status:  closed 
    Priority:  normal                              |    Milestone:         
   Component:  Compiler                            |      Version:  6.6.1  
    Severity:  normal                              |   Resolution:  invalid
    Keywords:  MVar, UnsafePerformIO, typechecker  |   Difficulty:  Unknown
          Os:  Unknown                             |     Testcase:         
Architecture:  Unknown                             |  
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Comment (by igloo):

 GHC implements Word8 with a 32 or 64 bit word (depending on the word size
 of your machine):
 {{{
 data Word8 = W8# Word#
 }}}
 All the primitive functions are careful to make sure that only 8-bit
 values are stored in the word, with a narrow8Word# primitive, e.g.:
 {{{
 (W8# x#) + (W8# y#)    = W8# (narrow8Word# (x# `plusWord#` y#))
 }}}
 The show function for Word8 works by showing the internal word as an Int,
 which is fine as long as the Word8 is valid.

 I hope that clears it up for you!

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1683>
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