[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
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        Reporter:  Isaac Dupree      |                Owner:  osa1
            Type:  feature request   |               Status:  new
        Priority:  low               |            Milestone:  ⊥
       Component:  Compiler          |              Version:  7.7
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by alexbiehl):

 I'm sorry, I falsely implied the context of this thread. I think the
 general idea is described in
 https://ghc.haskell.org/trac/ghc/wiki/UnliftedDataTypes. I noticed the
 conversation here got stalled so I picked up and experimented where osa1
 left:

 https://ghc.haskell.org/trac/ghc/ticket/1311#comment:12 describes a
 construct like the following:

 {{{
 type Unlifted = TYPE 'UnliftedRep

 newtype Blah :: TYPE 'IntRep where
   Blah :: Int# -> Blah

 data T :: Unlifted where
     T :: Int -> Int -> T

 }}}

 Which allows:

   1. newtype declaration over unlifted types
   2. data declarations which are represented through an unlifted pointer
 (do not contain bottom)

 The approach mentioned on `UnliftedDataTypes` page introduces a new
 keyword `unlifted`. This approach differs in that we give the unlifted
 representation through an explicit kind signature on the newtype/data type
 instead of a new syntax.

 And that is what the patch allows in
 https://ghc.haskell.org/trac/ghc/ticket/1311#comment:18 enables us to
 write.

 I can formulate a proposal next week.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1311#comment:20>
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