Unlifted primop types

Ben Gamari ben at smart-cactus.org
Wed Aug 22 11:45:26 UTC 2018

Simon Peyton Jones <simonpj at microsoft.com> writes:

> |  Huh! It looks like what we currently do for some primops is just use a
> |  totally bogus kind. For example, mkWeak# will happily accept an Int# as
> |  its first argument.
> Well, I see
>   primop  MkWeakOp "mkWeak#" GenPrimOp
>      o -> b -> (State# RealWorld -> (# State# RealWorld, c #))
> and I believe (from Ben's message) that the "o" means "open type variable",
> which is the old terminology for what we now call levity-polymorphic.
Right; currently (largely for historical reasons) we use `o` to
accommodate cases that accept both lifted and unlifted pointers. 


- Ben

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