Unpacking sum types

[Simon Peyton Jones]

|  I see, but then you can't have multiple fields, like
|  
|     ( (# Int,Bool #) |)
|  
|  You'd have to box the inner tuple too.  Ok, I suppose.

Well of course!  It's just a parameterised data type, like a tuple.  But, just like unboxed tuples, you could have an unboxed tuple (or sum) inside an unboxed tuple.

    (# (# Int,Bool #) | Int #)

Simon

|  -----Original Message-----
|  From: Simon Marlow [mailto:marlowsd at gmail.com]
|  Sent: 08 September 2015 09:55
|  To: Simon Peyton Jones; Johan Tibell; Ryan Newton
|  Cc: ghc-devs at haskell.org
|  Subject: Re: Unpacking sum types
|  
|  On 08/09/2015 09:31, Simon Peyton Jones wrote:
|  > |  How did you envisage implementing anonymous boxed sums?  What is
|  > | their  heap representation?
|  >
|  > *Exactly* like tuples; that is, we have a family of data type
|  declarations:
|  >
|  > data (a|b) = (_|) a
|  >             | (|_) b
|  >
|  > data (a|b|c) = (_||) a
|  >               | (|_|) b
|  >               | (||_) c
|  > ..etc.
|  
|  I see, but then you can't have multiple fields, like
|  
|     ( (# Int,Bool #) |)
|  
|  You'd have to box the inner tuple too.  Ok, I suppose.
|  
|  Cheers
|  Simon
|  
|  
|  > Simon
|  >
|  > |
|  > |  One option is to use some kind of generic object with a dynamic
|  > | number  of pointers and non-pointers, and one field for the tag.
|  > | The layout  would need to be stored in the object.  This isn't a
|  > | particularly  efficient representation, though.  Perhaps there
|  could
|  > | be a family of  smaller specialised versions for common sizes.
|  > |
|  > |  Do we have a use case for the boxed version, or is it just for
|  > | consistency?
|  > |
|  > |  Cheers
|  > |  Simon
|  > |
|  > |
|  > |  > Looks good to me!
|  > |  >
|  > |  > Simon
|  > |  >
|  > |  > *From:*Johan Tibell [mailto:johan.tibell at gmail.com]  > *Sent:*
|  01
|  > | September 2015 18:24  > *To:* Simon Peyton Jones; Simon Marlow;
|  Ryan
|  > | Newton  > *Cc:* ghc-devs at haskell.org  > *Subject:* RFC: Unpacking
|  > | sum types  >  > I have a draft design for unpacking sum types that
|  > | I'd like some  > feedback on. In particular feedback both on:
|  > |  >
|  > |  >   * the writing and clarity of the proposal and
|  > |  >
|  > |  >   * the proposal itself.
|  > |  >
|  > |  > https://ghc.haskell.org/trac/ghc/wiki/UnpackedSumTypes
|  > |  >
|  > |  > -- Johan
|  > |  >
|  >