how to write a ghc primop that acts on an unevaluated argument?

[Edward Kmett]

Maybe test for laziness in the argument by just putting something in that
goes boom when forced, e.g. 'undefined'?


On Sun, Nov 23, 2014 at 2:04 PM, Carter Schonwald <
carter.schonwald at gmail.com> wrote:

> Hey All,
> as part of trying to get some fixups for how prefetch works into 7.10,
> i'm adding a "prefetchValue" primop that prefetchs the memory location of
> a lifted heap value
>
> namely
>
> several operations of the following form
>
> primop PrefetchValueOp1 "prefetchValue1#" GenPrimOp
>    a -> State# s -> State# s
>    with strictness  = { \ _arity -> mkClosedStrictSig [botDmd, topDmd]
> topRes }
>
> I'd like some feedback on the strictness information design by someone
> who's familiar with how that piece of GHC. the idea being that
> prefetchValue is lazy in its polymorphic argument (it doesn't force it, it
> just does a prefetch on the heap location, which may or may not be
> evaluated).
>
> https://phabricator.haskell.org/D350
>
> is the code in question. And i *believe* i'm testing for being lazy in
> that argument correctly.
>
> thoughts?
>
> many thanks!
> -Carter
>
>
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