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

[Carter Schonwald]

yup, i have that!

    wrapFetch prefetchValue0# (error "this shouldn't get evaluated")

in the test suite!

in contrast
    wrapFetch prefetchValue0# $! (error "this shouldn't get evaluated")
does explode

shall I add a "should fail" test with the latter? (it doesn't seem
worthwhile)

On Sun, Nov 23, 2014 at 3:53 PM, Edward Kmett <ekmett at gmail.com> wrote:

> 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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>>
>
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