is Unlifted Type == Primitive Type?

Richard Eisenberg rae at
Mon Jan 20 09:58:44 UTC 2020

The recent addition of -XUnliftedNewtypes means that user-defined newtypes ( <>) can indeed be unlifted and unboxed. There is also a proposal for more general unlifted data ( <>).

If the wiki is out of date, do you think you could update it?


> On Jan 20, 2020, at 9:45 AM, Csaba Hruska <csaba.hruska at> wrote:
> Hello,
> According to GHC Wiki <> it seems that only primitive types can be unlifted.
> Is this true in general? (i.e. no user type can be unlifted)
> <image.png>
> Does the Stg to Cmm codegen support compilation for a variable of user defined ADT as unlifted?
> i.e. some analysis proved that it is always a constructor and never a thunk.
> Thanks,
> Csaba
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