[GHC] #1311: newtypes of unboxed types disallowed - documentation bug and/or feature request

[GHC]

#1311: newtypes of unboxed types disallowed - documentation bug and/or feature
request
---------------------------+------------------------------------------------
  Reporter:  Isaac Dupree  |          Owner:         
      Type:  bug           |         Status:  new    
  Priority:  normal        |      Milestone:         
 Component:  Compiler      |        Version:  6.6.1  
  Severity:  normal        |       Keywords:         
Difficulty:  Unknown       |             Os:  Unknown
  Testcase:                |   Architecture:  Unknown
---------------------------+------------------------------------------------
Tested in 6.6.1 and today's 6.7 (which claims to be version 6.7.20070418),

 {{{newtype FastBool = FastBool Int#}}}

 doesn't work. However this is not documented in the unboxed-types
 documentation in the User's Guide that lists similar restrictions
 http://www.haskell.org/ghc/docs/latest/html/users_guide/primitives.html

 Similarly (maybe), in phantom type arguments, even in GADTs where kind
 inference could be at work

 {{{data Boo a where Boo :: Int# -> Boo Int#}}}

 doesn't work.

 I tried {{{newtype ( FastBool :: # ) = ...}}} , and {{{data Boo ( a :: # )
 where...}}} , which just confused GHC.

 Is there a reason that coercions of unlifted types shouldn't work, or is
 it just unimplemented?  (inspired by looking at GHC's
 compiler/utils/FastTypes.lhs and thinking that using newtypes instead of
 type synonyms in places like that would improve type-safety)

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1311>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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